EVALUATING PRODUCTION PRACTICE FEASIBILITY OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH

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1 EVALUATING PRODUCTION PRACTICE FEASIBILITY OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.) by JUSTIN WAYNE MOSS (Under the Direction of R. Scott Tubbs) ABSTRACT The climatic conditions of the southeastern U.S. may allow multiple cropping systems of peanut (Arachis hypogaea L.) with wheat (Triticum aestivum L.) to be a sustainable approach toward crop production. Field trials were conducted to determine the most effective cropping systems to maximize wheat and peanut yield potential, evaluate their economic viability and to establish an effective post-emergence herbicide program for the relay-intercropped (RI) treatments. Cropping systems included main-plot variations of double-crop (DC), (RI) and monocrop (MC) management. The DC treatments exhibited higher peanut and wheat yields compared to the RI systems. Sufficient weed control was attained across all treatments. Income above variable cost for the DC ($938 to $2577/ha) systems exceeded the potential of RI ($408 to $1537/ha) and most MC ($36 to $1922/ha) treatments in most years. Growers interested in producing peanuts and wheat in the same year would be at an advantage to use a DC system. INDEX WORDS: Arachis hypogaea, Triticum aestivum, Glycine max, Multiple cropping, Double-cropping, Relay-intercropping, Tramlines, Strip-tillage, Conventional-tillage, Tomato Spotted Wilt Virus, Planting date, Imidazolinone, Pyroxasulfone, Clearfield

2 EVALUATING PRODUCTION PRACTICE FEASIBILITY OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.) by JUSTIN WAYNE MOSS B.S. University of Georgia, 2009 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2012

3 2012 Justin Wayne Moss All Rights Reserved

4 EVALUATING PRODUCTION PRACTICE FEASIBILITY OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.) by JUSTIN WAYNE MOSS Major Professor: Committee: R. Scott Tubbs Nathan B. Smith Timothy L. Grey Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2012

5 iv DEDICATION I would like to dedicate this work to my family and friends who have always loved and supported me during this important stage in my life. Mom and Dad, you have never once waivered in encouraging me to obtain my goals and have always been there to pick me up during the tough times. To express my feelings with mere words cannot give due justice to the sheer love and admiration I have for you. Most importantly I would like to thank God for allowing me the opportunity to accomplish so much in life. Your guidance, love and infinite wisdom is all part of a grand plan you have for me and I look forward the journey ahead. Psalm 32:8 I will instruct you and teach you in the way you should go; I will counsel you with my eye upon you.

6 v ACKNOWLEDGEMENTS These last two and a half years have been a whirlwind and looking back, that time just flew by. I would like to begin by thanking Dr. Jerry Johnson who has mentored me through my undergraduate and graduate career. You have always been there to answer my questions and offer your advice and opinions on many difficult decisions. I am forever grateful for your support and confidence in me which has guided me to where I am today. Next I would like to thank my excellent committee members Dr. Timothy Grey and Dr. Nathan Smith. It was a pleasure to be able to get to work and learn from such down to earth individuals who would take time out of their busy schedules to mentor and guide me during my graduate program. The next group cannot be thanked enough for their help. Excellent technical assistance was provided by Chad Abbot, Paige Adams, Katie Davis, Josh Ott, Jason Sarver, Corey Thompson, Will Vance and Dylan Wann. Without you guys there is no way I could have completed my projects. Long hours and hard work were a common occurrence and you all were there until the end and I thank you for it. Last but certainly not least is Dr. Tubbs. You brought me into your program seeing potential in me that I did not know I had. I know I was a lot of work but you took so much of your time to teach and guide me to where I am now. You gave me the opportunity to learn and the experience to be successful, which I will never forget. Thank you for the great times, for teaching me so much and having faith in me.

7 vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS...v LIST OF TABLES...viii LIST OF FIGURES...ix CHAPTER 1 INTRODUCTION LITERATURE REVIEW...4 Multiple Cropping...4 Cover Crops/Conservation Tillage...8 Residual Weed Control...11 Objectives AGRONOMIC AND ECONOMIC COMPARISONS OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.)...14 Abstract...15 Introduction...15 Materials and Methods...17 Results and Discussion...22 Summary and Conclusions...27

8 vii 4 ASSESSMENT OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.)USING IMIDAZOLINONE AND PYROXASULFONE Abstract...39 Introduction...39 Materials and Methods...41 Results and Discussion...44 Summary and Conclusions SUMMARY AND CONCLUSIONS...54 SOURCES OF MATERIALS...56 REFERENCES...58 APPENDICES 68 A. Base University of Georgia (UGA) conventional peanut budget 68 B. Adjustment to base UGA peanut budget by production systems at Tifton and Plains, GA for the study AGRONOMIC AND ECONOMIC COMPARISONS OF DOUBLE-CROP AND RELAY-INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.)...71 C. Adjustment to base UGA peanut budget by production systems at Tifton and Plains, GA for the study ASSESSMENT OF DOUBLE-CROP AND RELAY- INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.) USING IMIDAZOLINONE AND PYROXASULFONE. 72

9 viii LIST OF TABLES Table 3.1. Wheat yields (kg/ha) for wheat management strategies at Tifton and Plains, GA from Table 3.2. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Tifton, GA 2009 and Table 3.3. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Plains, GA from Table 3.4. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for sub plot treatment effects at Tifton and Plains, GA from Table 3.5. Percent visual weed control for main plot treatment effects at Tifton, GA in Table 3.6. Income above variable cost ($/ha) for main plot treatment effects at Tifton and Plains, GA from Table 4.1. Wheat yields for wheat management strategies at Plains and Tifton, GA in Table 4.2. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Tifton, GA in Table 4.3. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Plains, GA in Table 4.4. Income above variable cost ($/ha) for main plot treatment effects at Plains and Tifton, GA in

10 ix LIST OF FIGURES Figure 3.1. Narrow-tramline relay-intercrop...35 Figure 3.2. Wide-tramline relay-intercrop.36 Figure 3.3. Damage to wheat from planting procedure in relay-intercrop 37

11 1 CHAPTER 1 INTRODUCTION Mounting concerns about the ever-increasing human population have resulted in questions regarding the ability of producers to keep up with the expanding demand for global food supplies. Reports have shown that the amount of arable land for food production has declined and production costs have continued to increase resulting in additional burdens placed on world producers (FAO, 2003). As these obstacles emerge, the search for solutions culminates into experimental trials which may prove effective in combating these problems. Farmers throughout the world are battling some of these issues with more efficient cropping systems, enabling them to cut costs while increasing production. Multiple cropping is one approach encompassing both double-cropping (DC) and relay-intercropping (RI) enabling growers to achieve two different crop yields in the same field in one year. Growers in the southeastern United States (U.S.) have posed questions regarding the viability of using multiple cropping strategies allowing them to capitalize on higher market prices for wheat within a given year. Given that the southeast is a major peanut (Arachis hypogaea L.) producing region, potential strategies could be developed towards the production of both peanut and wheat (Triticum aestivum L.) during a single production year. Throughout the world, wheat is one of the most widely produced grain crops of the eight primary cereal grains. Americans on average consume 36% of the wheat produced in the U.S., while 50% is exported to other countries, and the remaining crop is used for seed and animal feed (WORC, 2002). In 2010, the U.S. produced over 60 Tg of winter wheat at 3,110 kg/ha. Of

12 2 that, Georgia growers produced 133,000 t of soft red winter wheat, which is the only class of wheat currently grown in this area (NASS, 2011a). Peanuts are the edible seed of a peanut plant and are high in protein, oil and fiber (TAPC, 2010). The peanut plant is a legume, and through a symbiotic relationship with Bradyrhizobia bacteria it can fixate its nitrogen into a usable form (Elkan et al., 1980). In the U.S., the majority of peanut production goes toward food and confection products while throughout the world, over 50% of the peanuts grown go toward the production of oil (TAPC, 2010). In 2010, the U.S. ranked 4 th in world peanut production behind China, India and Nigeria by producing approximately 1.9 Tg (FAO, 2012). National Agricultural Statistics Service (NASS) projections show the U.S. planted approximately 526,000 ha of peanuts in Southeast growers planted a combined 365,000 ha [Georgia (227,000 ha), Alabama (75,000 ha), Florida (53,000 ha), and Mississippi (10,000 ha)] of peanuts in 2010 (NASS, 2010). Despite the fact that the southeastern U.S. isn t a major producer of wheat, in recent years wheat prices have hit record high levels resulting in an increased interest from farmers to capitalize on these prices (Buerkle, 2007). Combined with the fact that the Southeast is a major peanut producing region, this allows for increased interest from growers to gain a profitable yield from both crops in a single production year. As production input costs continue to rise, farmers are seeking to maximize their yield while being as efficient with their land utilization as possible. Wheat is sometimes grown as a winter cover crop in the southeast. When prices are high, some growers begin questioning if they can carry their wheat to harvest to capitalize on these prices. If a grower intends to plant peanuts in the field that has wheat, the question arises as to what is the greater sacrifice killing the wheat and missing out on wheat harvest in order to plant peanuts on time, or fertilizing and harvesting the wheat while pushing peanuts beyond the optimum planting

13 3 window (Beasley et al., 1997). Wheat is traditionally harvested in late May in the southeast (NASS, 1997), the delayed planting of peanuts reduces the likelihood of achieving maximum yield. This is even more of a concern for growers as you move north in the peanut belt due to cooler late season temperatures. Cold temperatures can slow or even halt maturation of peanuts and negatively affect yield. Furthermore, adequate weed control programs within relay-systems must be identified due to regulations limiting herbicide applications before wheat harvest. Dilemmas such as these have given rise to research comparing RI and DC systems of peanut with wheat. Growers throughout the United States have addressed a similar issue by RI soybean (Glycine max [L.] Merr.) with wheat (Buehring et al., 1990; Chan et al., 1980; Duncan et al., 1990; Hammond and Jeffers, 1990; McBroom et al., 1981a, b; Moomaw and Powell, 1990; Porter and Khalilian, 1995; Reinbott et al., 1987). A similar system of RI peanut with wheat may provide growers the potential to achieve an earlier planting date for peanuts compared to DC while still getting a harvestable wheat crop. This intercropping strategy also may reduce the impact of tomato spotted wilt virus (Tospovirus) (TSWV), on peanut since thrips damage is usually reduced in areas where crops or crop residue are present (Baldwin and Hook, 1998; Kemerait et al., 2012; Culbreath et al., 2010; Jordan et al., 2003; Marois and Wright, 2003). After wheat harvest, the peanut seedlings will already be established and continue their growth cycle up until peanut digging. It is very important to analyze and understand the varying strategies involved in multiple cropping before implementation. Currently there is no published data researching the practicality of intercropping peanut with wheat. Information is needed to aid in critical production decisions for growers seeking to capitalize on both markets.

14 4 CHAPTER 2 LITERATURE REVIEW Multiple Cropping Multiple cropping is defined as the production of multiple crops in the same field within one year (Jones, 1991). This term can be further broken down into categories including intercropping and double-cropping (DC). Relay-intercropping (RI) systems seek to allow growers to simultaneously grow two crops in the same field for a period of time, before harvesting the reproductively mature first crop and allowing the second crop to continue its growth cycle (Jones, 1991). Double-cropping is the practice of producing two crops in the same area at different times within a given year (Howard and Lessman, 1991). Multiple cropping systems allow growers to be more efficient with their land use while implementing sustainable agriculture techniques. Utilization of these cropping systems can have positive weed control aspects resulting in lower weed escapes. Crops sown in the fall can become well established before winter and spring weeds become prevalent thus giving the cash crop a competitive edge and potentially reducing the use of herbicides (Horwith, 1985; Weil and McFadden, 1991). Previous studies have shown that multiple cropping systems have been effective in decreasing insect pests and disease damage in some areas by diversifying the crop species within the cropping system. By introducing new plant species within these systems, they can serve as a non-host for certain insects and diseases thus reducing these incidences (Hammond and Jeffers, 1990; Martin et al., 1989). An appealing aspect of multiple cropping to producers is that these

15 5 systems may allow growers to capitalize on market prices for two crops during a single production year. Throughout the U.S., DC is a practice adopted by growers seeking to benefit from increased production. One of the common cropping strategies entails the harvesting of winter wheat in late spring or early summer and planting soybean in the same field for harvest in the fall. A downfall with this system is that success varies from year to year. By carrying the wheat grain to maximum yield, it delays the planting of the second crop, thus running the risk of cooler fall temperatures reducing yields. Double-cropping soybean or peanut with wheat may prove economical in the South. But the farther north you go, the grower faces a greater risk of stand failure or lower yields due to the shorter growing season (Porter and Khalilian, 1995; Reinbott et al., 1987). When growers look to implement a DC system, several factors affect the yield potential of the crop such as soil moisture, amount of residue, and timing. Growers must be conscious of the amount of wheat residue left following harvest for it may interfere with a peanut planting operation. The amount of soil moisture following the wheat harvest is important for determining the potential for proper stand establishment. For peanut germination to occur, the seed moisture needs to reach 35% (Beasley, 2007). If the subsoil has been depleted of moisture by the wheat crop, then irrigation or rainfall must occur for germination and proper growth. It is recommended that growers irrigate before planting, but planting is not encouraged before a cool rain because it can slow germination and increase risk for disease. The soil temperature for proper germination of peanuts must be approximately 18 degrees Celsius at the 10 cm soil depth for a minimum of three consecutive days (Beasley, 2007).

16 6 The growing season for implementing a DC strategy would be more feasible in the southeastern U.S. than other parts of the country due to a longer growing season. Late season temperature fluctuations may pose problems for some growers in the U.S. when seeking to attain a DC with a late season planting of peanuts. The climate in the Southeast may be the optimal location for this strategy due to the prolonged growing season. Due to the associated risk with planting a soybean or possibly a peanut crop after harvesting the winter wheat crop, the implementation of a strategy to lengthen the growing season of the second crop may prove beneficial to growers. Relay-intercropping has been examined as a possible method of reducing the risks of growing two crops each year in the same field and in extending the northern limits of a two crop system. In the onset, RI systems did not receive much attention in the U.S. due to minimal equipment and implements geared toward planting, harvest and maintenance of RI fields (Jones, 1991). Another issue with implementing this system is the limited amount of weed control associated with this strategy. Due to regulations limiting the application of herbicides, the second crop could be subject to a span of 3-5 wk without any chemical weed control. Thus, a proper post emergent (POST) herbicide regimen needs to be established. There are advantages and disadvantages to RI systems compared to other cropping scenarios. More research is needed to fully explore the potential of such systems and to minimize the negative impacts of its flaws. Studies have sought to determine the effect of RI on soybean growth and yield when grown with winter wheat. In one study, the researchers were looking to determine if shading and other influences of wheat negatively affected the soybeans (Wallace et al., 1992). The study showed that the shading created by the wheat crop in the intercropping system caused significant differences in the growth of soybean plants early in the season compared to the control. These

17 7 effects did not always persist throughout the rest of the growing season. The growth response in the intercropped soybean is common in sun-adapted crops grown in a shade environment (Fitter and Hay, 1987; Wallace et al., 1992). The influence of the shading from this environment was more pronounced in soybean growth when optimum wheat stands were attained or when the time lapse between soybean planting and wheat harvest was longer (Wallace et al., 1992). The study goes on to report that soybean development in this intercropping system was more pronounced early in the season with less vegetative growth and smaller stem diameters compared to the control, but late season growth was similar in comparison and there were no apparent differences in yield (Wallace et al., 1992). These results bode well for growers in environments where the period of overlap between wheat and soybean crops is relatively short and thus negative effects of RI on early soybean growth may not result in yield reductions (Wallace et al., 1992; Rao and Mittra, 1988). Despite these findings, soybean yield reductions from RI (as compared with mono-cropping (MC)) have been reported in Missouri, Kansas, Nebraska, and Illinois (Chan et al., 1980; Duncan et al., 1990; McBroom et al., 1981a, b; Moomaw and Powell, 1990; Reinbott et al., 1987; Wallace et al., 1992). Other studies conducted in Mississippi and South Carolina have shown that RI yields were equal to yields of a MC (Buehring et al., 1990; Wallace et al., 1992). Wallace et al. (1992) claims that the main differences between midwestern and southern locations may be related to the duration of overlap between the wheat and soybean crops. Depending on the length of time between sowing soybean and harvesting wheat in a RI system, the growth affects on soybean may be confined to early season growth with minimal to little effect on yield (Wallace et al., 1992). Findings such as these provide a positive outlook in determining if a similar intercropping system will work on peanuts grown with wheat.

18 8 Cover Crops/Conservation Tillage Conservation tillage is defined as the use of a moldboard plow for primary tillage followed by use of implements such as harrows to prepare seedbed (Gebhardt et al., 1985). Growers who practice conservation tillage also may seek to implement the use of cover crops to gain additional benefits (Balkcom et al., 2007). The benefits of conservation tillage include reduced soil erosion, improved soil quality and increased availability of water for crop production. The use of cover crops can further benefit conservation tillage systems by producing crop residues that help control weeds, increase soil organic matter, improve soil structure, increase water infiltration, and reduce the potential for soil erosion. When looking to improve the physical properties of soil, Balkcom et al. (2007) claim that the key factors are: crops grown, soil type, residue management, temperature and rainfall. The benefits of cover crop use associated with the increased amount of organic matter in the soil will be negated in proportion to the tillage methods used. Conventional tillage deteriorates soil organic matter faster than some conservation tillage methods such as no-till and strip tillage. Improvements in soil physical properties with cover crops have been documented widely in conservation tillage systems (Baumhardt and Lascano, 1996; Bruce et al., 1992; Dabney et al., 2001; Delgado et al., 1999; Delgado et al., 2006; Duiker and Myers, 2005; Langdale et al., 1992, Peterson et al., 1998, Truman et al., 2005). The use of cover crops has several benefits toward the improvement of soil and water quality such as the production of more vegetative biomass which helps reduce surface runoff and velocity, increases water infiltration and helps transpire water (Dabney et al., 2001). The need for cover crops is greatest in the southern parts of the U.S. where oxidation of organic matter is greater because of higher temperatures (Duiker and Myers, 2005). Thus by using conservation

19 9 tillage, organic matter present in the soil will not be broken down due to oxidation as rapidly as when using intensive tillage methods. Wheat can be grown as a cash crop for many producers in the U.S., but winter wheat can provide many benefits when grown as a cover crop. Wheat is not as likely as barley (Hordeum vulgare L.) or rye (Secale cereale L.) to become a weed, it is easier to eradicate, it is cheaper and easier to manage than rye, and maturation takes longer than other cereal grains therefore there is more flexibility in its termination which is beneficial in an intercropping system (Balkcom et al., 2007). Winter wheat can provide over-wintering cover to reduce soil erosion for most parts of the U.S. (Brinsfield and Staver, 1991). Wheat grown as an over-wintering cover crop does not require fertilizer (Balkcom et al., 2007). Balkcom et al. (2007) go on to report that approximately 80% of the K remains in the field if the stems and leaves from the wheat are not removed at harvest, and when the wheat is managed as a cover crop, all of the nutrients are recycled leaving behind excess N to be scavenged by the following crop. When wheat is seeded in the fall, it can become well established with its rapid spring growth choking out many weeds (Canadian Organic Growers Inc., 1992). Although wheat provides fast and effective weed suppression, growers must use pre-emergent (PRE) and POST herbicide applications to provide sufficient weed control (Price et al., 2006). From a pest management perspective, when wheat is managed as a cover crop, it rarely poses an insect or disease risk (Balkcom et al., 2007). The residues from cover crops have been associated with a reduced occurrence of many diseases in varying crops. The use of small grains as cover crops in conservation tillage systems has been shown to lessen the impact of TSWV on peanut yields, and this effect is directly related to the decreased incidence from thrips that vector this virus (Kemerait et al., 2012). These findings provide for increased optimism when seeking to establish a peanut with wheat intercropping

20 10 system. Based on this information, the presence of wheat as a cover or cash crop in the field has the potential to provide several benefits to the grower including decreased weed pressure, reduced TSWV damage in peanuts, and increased economic returns. The most common type of conservation tillage implemented in peanut production is striptillage. Strip-tillage employs minor tillage of a 7-cm to 30-cm band of soil with minimal disturbance of crop residue between rows. Seed are then planted into the tilled bands allowing good seed-to-soil contact (Derpsch, 2003; Gallaher and Hawf, 1997; Johnson et al., 2001; Logan, 1990). This system clears residue from row area to allow pre-plant soil warming and drying. Strip-tillage has several benefits over conventional tillage which include reduced soil erosion, increased organic matter in the soil and decreased soil water evaporation. Although strip-tillage has advantages over conventional tillage plots, studies have shown that there are a few drawbacks to the system. Jordan et al., (2003) claimed that pod yield in conventional tillage systems equaled or exceeded that of strip-tillage directly into crop stubble in 16 of 17 experiments conducted. Similar studies have confirmed smaller pod-yields in striptillage scenarios (Gebhardt et al., 1977; Wilcut et al., 1990). Despite these claims, additional research has been conducted on strip-tillage in which the increased presence of soil organic matter, reduced soil erosion and improved tilth have caused consistently equal or higher yield as conventionally tilled peanut (Johnson et al., 2001; Tubbs and Gallaher, 2005; Wright et al., 2000). Other issues associated with strip-tillage relate to plant stand. Due to increased amounts of residue present in strip-till situations, seed placement may become an issue. Advancements in technology, such as the use of row cleaners, have helped to address this issue but continued improvements are needed for this system.

21 11 The combination of using wheat as cover and conservation tillage systems may provide many benefits for the advancement of MC peanut strategies. One key benefit with strip-tillage systems is its effect on TSWV. Research shows there are higher levels of TSWV incidence in conventional tillage systems compared to strip-tillage when planting into residue from the previous crop (Baldwin and Hook, 1998; Johnson et al., 2001; Wright et al., 2000). Along with reduced incidences of TSWV, strip-tilled peanuts with plant residue on the ground had higher yields under high stress conditions (lack of rain and high temperatures) (Johnson et al., 2001; Jordan et al., 2003; Marois et al., 2003; Wright et al., 2000). Residual Weed Control Rising input costs in crop production continue to burden growers seeking higher revenue potential. This is especially evident to producers who implement multiple cropping systems. One obstacle is attaining sufficient weed control in order to maximize yields. Strategies for weed control must be developed in order to inform growers of the most cost effective means for production while achieving adequate management. In peanut production, there are several herbicide regimens which can provide excellent control, however some herbicide programs are expensive and not applicable in RI systems. Identifying herbicide programs which provide residual control may provide cost-effective means for multiple-cropping systems of peanut with wheat. Clearfield 1 systems allow for broad-spectrum residual control of grass and broadleaf weeds. Clearfield crops exhibit tolerance to imidazolinone herbicides which control weeds by blocking production of the essential amino acids valine, leucine, and isoleucine by inhibiting the enzyme acetolactate synthase (ALS) (Colquhoun et al., 2003; Tan et al., 2005). The first

22 12 commercial launch of an imidazolinone tolerant crop occurred in 1992 with maize (Zea mays L.). Since then, several imidazolinone tolerant crops have been released, including wheat (Tan et al., 2005). Clearfield wheat varieties were developed using traditional plant breeding methods and thus are not considered a genetically modified organism (Colquhoun et al., 2003). The imidazolinone herbicide imazethapyr was registered for use in peanut in 1991 and at the time was the first herbicide to provide broad spectrum residual control of broadleaf weeds and perennial sedge (Wilcut et al., 1994). Growers looking to implement an imidazolinone herbicide into their weed control program should be aware that they could face planting restrictions on certain crops they plan to rotate. The development of Clearfield wheat coupled with imidazolinone registration in peanut may allow for lower herbicidal input costs for growers while attaining adequate control. This potential benefit may be well suited for implementation into a RI system of peanut with wheat. Another potential option for attaining broad-spectrum residual weed control is through use of the herbicide pyroxasulfone. Pyroxasulfone controls weeds by inhibiting very-long-chainfatty acids, thus it is classified within the K3 group of herbicides (Tanetani et al. 2009; Senseman, 2007). Development of this herbicide is currently being geared towards PRE use in corn, soybean, and wheat (Prostko et al., 2011). There is very little information available about legume crop tolerance to pyroxasulfone, however Prostko et al., (2011) found that peanut yields were not reduced by any rate or timing of the herbicide. Assessment of pyroxasulfone used within RI systems may provide a viable option for growers looking to attain adequate weed control while reducing input costs. Furthermore, growers who rotate crops will not face the same planting restrictions associated with imidazolinone herbicides.

23 13 Objectives Currently, there is no published data researching the practicality of intercropping peanut with wheat. Farmers are seeking to maximize the profitable use of their land while minimizing their input costs. As a result, research needs to be conducted to identify the most practical approaches to achieve an economically sustainable method for intercropping peanut with wheat. Similar studies have been conducted by growers throughout the U.S. on soybean and wheat, which can be adapted to fit this potential cropping system. In these projects, economic assessment will be conducted to determine the viability of RI and DC systems of peanut with wheat in terms of profitability. These projects will also be evaluated to determine the most effective weed control strategies for RI in order to attain optimum peanut and wheat yields. Ancillary data on the incidence of TSWV in peanut will be analyzed to determine if the established wheat crop provides benefits on reducing the severity/incidence of this infection.

24 14 CHAPTER 3 AGRONOMIC AND ECONOMIC COMPARISONS OF DOUBLE-CROP AND RELAY- INTERCROPPING SYSTEMS OF PEANUT (ARACHIS HYPOGAEA L.) WITH WHEAT (TRITICUM AESTIVUM L.) 1 1 Moss, J.W., R.S. Tubbs, T.L. Grey, N.B. Smith, J.W. Johnson, and J.W. Davis. Submitted to Crop Management, 03/22/12.

25 15 Abstract: The climatic conditions of the southeastern U.S. may allow multiple cropping systems of peanut (Arachis hypogaea L.) with wheat (Triticum aestivum L.) to be a sustainable approach toward crop production. The objectives of this project were to determine the agronomic, economic and weed control viability of double-crop (DC) and relay-intercropping (RI) systems of peanut with wheat. A split-plot design was used with eight cropping systems including variations of DC, RI and monocrop (MC) management as main-plots and a sub-plot effect of three peanut cultivars. Studies were conducted in Tifton, GA in 2009 and 2011 and Plains, GA in 2010 and DC peanut with wheat yielded greater than the RI systems. Comparison of yield, grade and tomato spotted wilt (Tospovirus) incidence among genotypes favored Georgia-06G and Tifguard ahead of Georgia Green. Sufficient weed control was attained across all treatments in 2010 and 2011 but not in the RI plots in Income above variable cost for the DC ($938 to $1875/ha) systems exceeded the potential of RI ($408 to $1210/ha) and most MC ($36 to $1671/ha) treatments. Growers interested in producing peanuts and wheat in the same year would be at an advantage to use a DC system. Introduction In the southeastern US, 208,000 ha of wheat were produced on average from 2009 to 2011 in the peanut producing states of AL, GA, FL, and SC (NASS, 2011a.). Higher wheat prices have resulted in growers seeking alternative methods to capitalize on this potential market. Given this is also a major peanut producing region (NASS, 2011b.), it has allowed for increased interest from growers to gain a profitable yield from both crops in a single growing season. As production input costs continue to rise, farmers are seeking to maximize yields while being efficient with land utilization. The implementations of multiple cropping systems for peanut have

26 16 potential in the southeastern U.S. due to a prolonged temperate growing season. Full season wheat production can cause peanut planting to be later than optimally desired for maximum yield potential. When moving north in the peanut belt of the southeast, cooler late season temperatures can delay or halt peanut maturity and negatively affect yield potential. During wheat planting in the southeast, the establishment of tramlines spaced 91 cm apart could allow peanut to be planted several wks prior to wheat harvest. Tramlines are unplanted rows which allow tractor and implement wheels to travel without damage to the crop and are often used in wheat to facilitate soybean planting (Prochaska, 2001). Wheat and peanut would then co-exist in the field for a short period of time; as peanut is emerging and wheat is maturing. This situation could also impact tomato spotted wilt (Tospovirus) (TSWV) incidence since thrips damage on peanut is usually reduced where a previous crop or crop residue remains on the soil surface (Kemerait et al., 2012). Researchers throughout the U.S. have addressed similar multi-crop production issues by relay-intercropping (RI) soybean (Glycine max [L.] Merr.) with wheat (Buehring et al., 1990; Chan et al., 1980; Duncan et al., 1990; Porter and Khalilian, 1995; Reinbott et al., 1987). Although studies reported soybean had reduced yields from RI (Chan et al., 1980; Duncan et al., 1990; Reinbott et al., 1987). Buehring et al. (1990) reported that RI yields were equal to yields of a mono-crop (MC). A similar system of RI peanut with wheat may provide growers the potential to achieve an earlier planting date to minimize the impact of late season cool temperatures while also obtaining a harvestable wheat crop. A possible issue with implementing this system however is the potential for limited weed control with this strategy. Preplant and pre-emergence (PRE) herbicides for peanut are usually applied before 24 h after planting. Due to label restrictions limiting the application of herbicides before wheat harvest, the peanut crop will be subjected to two to four wks without any chemical weed control. Therefore, the primary

27 17 objective of this research is to identify practical approaches to achieve an economically sustainable method for producing peanut and wheat crops within the same year using different cropping systems. A secondary objective is to evaluate commonly used PRE and post-emergence (POST) herbicides for use in these cropping systems. Materials and Methods Irrigated field trials were conducted on a Tifton loamy sand (fine-loamy, kaolinitic, thermic Plinthic Kandiudults) (USDA-NRCS, 2012) at the USDA Belflower farm in 2009 and at the University of Georgia (UGA) Lang-Rigdon farm in 2011 both near Tifton, GA. These trials were also conducted under irrigation on a Greenville sandy loam (fine, kaolinitic, thermic Rhodic Kandiudults) (USDA-NRCS, 2012) at the UGA Southwest Research and Education Center near Plains, GA in 2010 and The soft red winter wheat genotype AGS 2020 (PI ) was planted using a Tye Pasture Pleaser no-till grain drill 2 on 20 November 2008 and 2009 at corresponding locations, and on 23 and 30 November 2010 at Plains and Tifton, GA respectively. Wheat was planted at a depth of 1.9 cm and seeding rate of 101 kg/ha at Tifton, GA, and 129 kg/ha at Plains. Land preparation involved disk-harrowing to a smooth surface and seed beds were delineated to each plot on 1.8 m wide beds. Wheat seed, treated with difenoconazole plus metalaxyl-m fungicides 3 were drilled in rows (10 rows per bed) at 9, 25, 42, 58, and 75 cm on either side of the center of the bed. In order to establish tramlines for the RI plots, the third wheat drill row (42 cm on either side of bed center) was plugged for treatment 1, and the third (42 cm) and fourth (58 cm) wheat drill rows on either side of bed center were plugged for treatment 2, and seed flow per drill adjusted accordingly to keep seeding populations consistent. All fertilizer requirements followed UGA Extension recommendations (Harris, 2011).

28 18 Cover crops for treatments 3 and 4 were terminated with glyphosate 4 (1.54 kg a.i./ha) approximately three to four wks before planting. Wheat maturity was determined using the Feekes scale (Feekes, 1941; Large, 1954). All wheat managed for grain treatments 1, 2, 6, and 7 was harvested using a Wintersteiger single-plot combine 5 on 2 June 2009 and 25 May 2010 at corresponding locations and on 17 and 18 May 2011 at Plains and Tifton respectively. The wheat crop was then dried and the overall yield was determined. Eight main plot cropping regimes were tested: 1. Narrow-tramline relay-intercrop (Fig. 3.1) wheat planted on 1.8 m beds with one skipped row (tramline approx. 33 cm wide; 8 wheat rows per bed) for peanut to be planted in early May. Wheat harvested for grain in late May or early June after several wks of co-existence with peanut.[nri] 2. Wide-tramline relay-intercrop (Fig. 3.2) wheat planted on 1.8 m beds with two skipped rows (tramline approx. 49 cm wide; 6 wheat rows per bed) for peanut to be planted in early May. Wheat harvested for grain in late May or early June after several wks of coexistence with peanut. [WRI] 3. Strip-till planting of peanut into a killed cover crop of wheat (peanut planted early May). [STWC] 4. Conventional tillage planting of peanut into a prepared seedbed after wheat is killed and residues incorporated into soil (peanut planted early May). [CTWC] 5. Peanut alone (no wheat planted) planted into conventionally turned seedbed in early May. [EP]

29 19 6. Double crop of peanut planted after a solid-planted wheat crop (rows approx. 19 cm apart, no skipped rows; 10 wheat rows per bed) has been harvested for grain after maturity, peanut planted in late May or early June, strip-till into wheat stubble and residue after harvest. [DCST] 7. Double crop of peanut planted after a solid-planted wheat crop (rows approx. 19 cm apart, no skipped rows; 10 wheat rows per bed) has been harvested for grain after maturity, peanut planted in late May or early June, conventional tillage prepared seedbed after incorporating wheat stubble and residue after harvest. [DCCT] 8. Peanut alone (no wheat planted) planted into conventionally turned seedbed in early June. [LP] Three commonly produced peanut genotypes in the southeastern U.S. were planted as a sub-plot effect including Georgia Green (Branch, 1996), a small-seeded runner type; Georgia- 06G (Branch, 2007), a large-seeded runner type; and Tifguard (Holbrook et al., 2008), a largeseeded runner type. Early planted peanut treatments 1-5 were seeded 10 May 2010 and 9 May 2011 in Plains, and 8 May 2009 and 5 May 2011 at Tifton, GA. Late planted peanut treatments 6-8 were seeded on 2 June 2010 and 31 May 2011 in Plains, and on 9 June 2009 and 24 May 2011 at Tifton. All plots were planted with a two-row Monosem precision air planter 6 at a depth of 5 cm with a seeding rate of 20 seed/m, and a standard row spacing of 91 cm. All seed were treated with azoxystrobin plus fludioxonil plus mefenoxam 7 fungicide seed treatment. Peanut maturity was determined each year using the standard hull scrape method (Williams and Drexler, 1981). Peanuts were inverted on 2 October 2009, 29 September 2010, 15 September 2011 for Georgia Green at Tifton, 29 September 2011 for Georgia-06G and Tifguard

30 20 at Tifton and 3 October 2011 at Plains for the early planted treatments. Late planted peanuts were inverted on 5 November 2009, 20 October 2010, 23 October 2011 at Plains and 24 October 2011 at Tifton. Harvest for the early planted peanuts occurred 10 October 2009, 1 October 2010, 19 September 2011 for Georgia Green at Tifton, 4 October 2011 for Georgia-06G and Tifguard at Tifton and 7 October 2011 at Plains. Late planted peanuts were harvested 10 November 2009, 26 October 2010, 27 October 2011 at Plains and 28 October 2011 at Tifton. All peanut plots were inverted using a two-row KMC digger-shaker-inverter 8 and harvested using a two-row Lilliston peanut combine. Each genotype was evaluated for pod yield, grade (total sound mature kernels) and percent incidence of TSWV. Ratings for TSWV were conducted on 21 September 2009, 21 September 2010, 14 September 2011 at Tifton and 23 September 2011 at Plains. Economic analysis was used to determine the system profitability of producing a wheat and peanut crop for each year. Production practices for peanut included conventional deep tillage: disk-harrowing, deepturning with a mold-board plow to a depth of 30 to 35 cm, and rotary-tilling to form peanut beds in treatments 4,5,7, and 8. A two-row Unverferth strip-till implement 9 with sub-soil shanks and ground-driven crumblers to fill seed bed was used for creating a 17.8 cm wide seedbed and to a depth of 30.5 cm during land preparation before planting peanut in treatments 3 and 6. No tillage was utilized in treatments 1 and 2, as peanut was planted into actively growing wheat. Plots consisted of two beds (four rows) measuring 3.7 m x 12.2 m, except in 2011 at Plains where the plots measured 3.7 m x 11.6 m due to field dimensions. Gypsum 10 and boron 11 applications were made according to UGA recommendations for peanut (Harris, 1997). Fungicide applications followed guidelines set forth by the high risk model of the Peanut Disease Risk Index (Kemerait et al., 2012). Herbicide applications for treatments 3-8 were: pendimethalin 12 (930 g a.i./ha) plus

31 21 diclosulam 13 (27 g a.i./ha) plus flumioxazin 14 (107 g a.i./ha) and watered in after peanut planting. Treatments 1 and 2 followed a POST herbicide program since there was still active wheat growing in the plots. After wheat harvest, these plots received an application of paraquat 15 (140 g a.i./ha) plus bentazon (370 g a.i./ha) and acifluorfen 16 (190 g a.i./ha) plus S-metolachlor 17 (1.1 kg a.i./ha) applied before 28 days after peanut cracking for weed control. These plots also received 2,4- DB 18 (280 g a.i./ha) with the first two fungicide applications as well as clethodim (140 g a.i./ha) plus 1% v/v crop oil concentrate as needed for grass control. Clethodim 19 was added to the POST herbicide protocol after the 2009 growing season to control grasses. Visual weed ratings were conducted on 30 September 2009 to determine the percent weed control for main plot treatment effects. Weed control ratings for other years were not conducted because weeds were not present. Economic assessment was determined using the UGA conventional peanut budget used as a base budget for expenses and adjusted for production practices according to treatment. Income above variable cost took into account all expenses incurred as a result of production. This calculation excludes fixed costs, management charges and land rent and if positive then it generally will be profitable in the short run. Statistical analyses were conducted using PROC GLIMMIX in SAS Data were analyzed by analysis of variance and differences among least square means were determined using multiple pairwise t-tests (P 0.05). There were significant year by main-plot and year by sub-plot interactions (P 0.05), thus all data was separated by year and subsequently analyzed.

32 22 Results and Discussion Cropping System and Genotype Performance Evaluation. Wheat production. As a result of using two-row equipment in managing these systems, findings were consistent with Buehring et al. (1990) in which there were issues with running over wheat rows with the tractor tires in the RI plots during peanut planting (Fig. 3.3). Thus, wheat yields (Table 3.1) were reduced 15 to 40% across years in the NRI system and by 26 to 70% in the WRI system compared to standard wheat management. Wheat yields were consistent by treatment across siteyears except for 2011-Tifton in which excessive heat and lack of rainfall during reproductive growth negatively affected harvest weights. Because of the limitations of using two-row equipment in these experiments, further research is needed to examine larger scale equipment common to many farms (i.e. six-row planters), which would cause less mechanical damage from tractor tires to the wheat during peanut planting. Another method would be to accommodate tramlines for the tractor tire. These practices could make RI of peanut with wheat more viable. Peanut production. In 2009, peanut yields (Table 3.2) in the early planted peanut treatments where there was either no wheat present (EP), or where wheat was managed as a cover crop (CTWC, STWC) were among the highest in yield. The late planted (LP, DCCT, DCST) and RI (WRI, NRI) systems resulted in lower peanut yields, however, cool temperatures in early October (below 10 C for three consecutive nights) may have negatively affected yields of the late planted peanut as a result of the plant slowing or ceasing maturity. However, late planted peanut following wheat harvest (DCCT, DCST) had higher grades and lower TSWV incidence than the earlier planted peanuts. The increased incidence of TSWV in the early planted treatments can be directly linked to the early planting date, as thrips populations and peanut susceptibility to infection are generally higher in early May (Kemerait et al., 2012). There was a

33 23 trend toward reduced TSWV incidence in the RI treatments compared to the other early planted peanuts. This data corresponds with Kemerait et al. (2012) for less thrips damage, and less TSWV has consistently been observed where more crop residue is present. It should also be noted that there was much heavier weed infestation in the RI plots, as the POST weed control regime was not adequate. This was a contributing factor in reduced peanut yields compared to the other early peanut plantings. The RI systems in this trial were also among the lowest for grade. Pod yields for the RI treatments at Tifton in 2011 (Table 3.2) were significantly lower than all other treatments. These findings are comparable to the results from Tifton All early-planted plots were similar in grade except for the NRI system which was lower than the EP and CTWC treatments. Incidences of TSWV were lower in the RI treatments in comparison to most of the other early-planted plots, similar to the There were no significant differences in grade or TSWV incidence among the late planted treatments. Excluding the RI treatments, peanut yields were not significantly different between all other treatments except for the DCST and the STWC plots. The late planted peanut treatments 6-8 in 2010 provided the highest yields plus grades among all treatments (Table 3.3). The early planted treatments 1-5 were dug approximately a wk late because of rain. That caused over-mature plants with deteriorating pegs, which likely increased digging losses leading to reduced yields. The incidence of TSWV was low in all treatments, although the CTWC and EP treatments were among the highest. The RI plots experienced the lowest peanut yields and grades among all treatments although not always statistically different. The lowered yields within the NRI and WRI plots can be explained through management practices used for those systems. No tillage was utilized in the RI

34 24 treatments, as peanut was planted into actively growing wheat. Due to low soil moisture at planting, optimum seed depth was not reached resulting in the seed not having optimum seed to soil contact. Peanut yields and grade among the early planted treatments were not statistically different from one another. The findings from Plains 2011 (Table 3.3) are mostly consistent with the results from Plains 2010 (Table 3.3). Pod yields in 2011 for the late planted peanut plots were anywhere from 6 46% higher than the early planted treatments compared to 3 27% in The DCST, DCCT, and LP treatments graded higher than all other treatments except for the EP plots and had the lowest incidence of TSWV. The RI treatments provided some of the highest yields among the early planted treatments and were not significantly different from the DCCT and DCST plots. This trend was not consistent with the data from the previous years. There were few differences in grade or TSWV among all early planted treatments or late planted treatments, although late planted treatments had preferred results over the early planted peanuts for both variables. It should be noted that 2011 was a hot and dry growing season especially during the spring into early summer. The lack of rain and excessive heat during pod set may have caused some pollen sterility, negatively affecting yields. Comparison of three sub-plot treatments (Georgia Green, Georgia-06G, and Tifguard) will provide better recommendations to growers when deciding which peanut genotypes to implement their production strategies. Georgia-06G and Tifguard were consistently among the highest yielding with some fluctuation between locations (Table 3.4). Although not always significantly higher, Georgia-06G yielded better than Tifguard in Plains, but the opposite occurred at the Tifton locations. Questions regarding the peg strength of Tifguard have previously arisen (C.C. Holbrook, pers. commun.,2012), although there is no published data at

35 25 this time to support or refute whether this cultivar has weaker peg strength than any other cultivar. However, data from the UGA Statewide Variety Testing Program (SWVTP) (Day et al., 2011) and Tubbs et al. (2011) have demonstrated that Tifguard does not perform as well in the sandy loam soil of Plains as it does in coarser textured soils such as loamy sands. This data is consistent with those results, thus there may be increased pod shed of Tifguard in finer-textured soils based on observations of a higher fraction of inverted pegs with no attached pod compared to other genotypes. Peanut grade fluctuated from year to year, however Georgia-06G consistently produced among the top-grades. Georgia Green typically had the lowest yield and greatest incidence of TSWV. Yield comparisons were consistent with the UGA SWVTP reports (Day et al., 2011). Despite Tifguard not being as competitive among the three genotypes at Plains, its excellent results in sandier soils and nematode resistance make it a viable option to growers needing to capitalize on its benefits (Brenneman et al., 2010). Georgia-06G and Tifguard are superior genotypes compared to Georgia Green, for improved TSWV resistance and higher yield potential. Assessment of PRE and POST Herbicide Regimen. Visual weed ratings were used to determine the effectiveness of control for the PRE and POST herbicide regimens. In 2009, ratings (Table 3.5) were conducted on the most prevalent weeds: crowfootgrass (Dactyloctenium aegyptium L.), smallflower morningglory (Jacquemontia tamnifolia L.), goosegrass (Eleusine indica L.), texas millet (Urochloa texana Buckl.) and purple nutsedge (Cyperus rotundus L.). There were no significant differences in control of texas millet and purple nutsedge among all treatments (data not shown). Control of smallflower morninglory was lowest in the RI plots compared to all other treatments. This can be explained due in part to bentazon and acifluorfen not having residual control (Prostko, 2011). Late emergence of smallflower morninglory may

36 26 have occurred due to the pre-established weed seed bank as well as restrictions on application timing which coincide with the diminished residual control of the herbicides (Wehtje et al., 1992). Despite this difference it is not believed that smallflower morninglory negatively affected overall yield due to this increased weed pressure. The WRI and NRI had significantly less control of crowfootgrass and goosegrass compared to the other systems. Weed densities for all species were approximately 1 to 3 plants/m 2. As a result of increased competition from grass weeds, clethodim was added to the POST herbicide protocol after the 2009 growing season to better assess production viability without negatively affecting yields from competition. The PRE herbicide regimen provided sufficient weed control for all species in corresponding treatments. These data indicate potential weed control challenges within the WRI and NRI systems although adequate control was witnessed in 2010 and Economic Analysis of Main Plot Treatment Effects. In 2009, the income above variable cost (IAVC) (Table 3.6) for the WRI plots were 27 73% lower than all other treatments. The DCST plots were among the highest with revenue 16 65% higher than all other treatments except for the EP. Results for 2010 showed both DCST and the DCCT plots providing the greatest economic advantage to growers. The two RI treatments were among the lowest in terms of income. Plains 2011 followed a similar trend as reported in 2009 and 2010 where both doublecropping (DC) treatments resulted in some of the highest income for producers. The RI plots however did not follow a similar pattern showing increased revenue than the previous years despite still being significantly lower than the DCCT and DCST treatments, which is attributed to higher yields for these systems in that location. In 2011 at Tifton, the DCST plots were significantly higher than all other treatments except for the CTWC plots. The relay-systems followed suit with the findings from 2009 and 2010 where they were again among the lowest in

37 27 terms of profit. Observing the trends across all years created a tendency though not always significant, in which the late planted peanut treatments especially the DC treatments had higher revenue potential in comparison to the early planted systems. Assessment of IAVC takes into account all costs excluding fixed costs, management charges, and land rent. Thus if positive, IAVC will generally produce a profitable income in the short-term. All treatments did provide revenue potential for growers, however DC peanut after wheat does provide an economic advantage over RI of peanut. The advantage of having a full wheat harvest as well as exhibiting some of the higher peanut yields appears to give the DC treatments an economic advantage over all other treatments though not always significantly higher. Summary and Conclusions Despite wheat production being relatively low in major peanut producing regions of the U.S., it is possible for growers to capitalize on both markets through implementation of cropping systems which produce both crops. Comparison of wheat yields among the RI and DC treatments definitively showed an advantage with the DC systems due to higher yields from a full wheat harvest. The relay-systems had lower wheat yields, but they provide space for peanut to be planted into the actively growing wheat during the optimum planting window for peanut. Peanut yields followed an unexpected trend in which the late-planted treatments tended to produce higher yields compared to the early treatments that were planted during the optimum planting window (Baldwin, 1997). Coupled with yield, peanut grade and TSWV incidence also followed a similar trend in which grades tended to be higher and TSWV incidence was lower with the late-planted treatments. It should be noted that there is a risk of cool fall temperatures slowing or ceasing the maturity of late planted peanuts in any given year because of the

38 28 unpredictability of the weather. There did not appear to be any major effect on yield in these trials related to cool temperatures (peanuts were near 130 days old or more in these trials when temperatures reached a threatening level). The RI systems were consistently among the lowest in terms of peanut yield. This is primarily attributed to the fact that there was no tillage practice used in these plots. No-till management has consistently resulted in lower yields than either conventional or strip-till peanut systems (Dowler et al., 1999; Grichar, 1998; Grichar and Boswell; 1987). Comparison of yield, grade and TSWV incidence among genotypes favored Georgia-06G and Tifguard ahead of Georgia Green. Tifguard s nematode resistance and strong performance in sandy soils make it a viable option for growers seeking these benefits, however it does not produce as well in finer textured soils. Comparison of weed control regimens for the relay-systems versus all other treatments provided similar results. Except for in 2009, in which the herbicide clethodim was not added to the POST herbicide protocol, sufficient weed control was attained across all treatments. The addition of clethodim allowed for proper assessment of the system s production viability without grass weeds limiting yields. Revenue of DC peanut with wheat currently exceeds the potential of RI as well as many other commonly used monocropping peanut systems. As a result of a year by main-plot interaction the average results for IAVC favor the DC systems. Most years the DC treatments were among the highest, if not the highest in revenue. The relay-systems were consistently in the middle to lower range of treatments in terms of revenue. It is believed that growers who seek to capitalize on both markets would be at an economic advantage to use a DC strategy for production of both peanut and wheat. Additional research is needed to improve management of RI systems to fully realize the benefits that such systems can provide.

39 29 Table 3.1. Wheat yields (kg/ha) for wheat management strategies at Tifton and Plains, GA from Location Years Cropping System a Tifton 2009 Plains 2010 Plains 2011 Tifton 2011 kg/ha Narrow-Tramline Relay 2556 b 2925 b 3254 b 2179 ab Wide-Tramline Relay 1278 c 3094 b 2825 b 1863 b Strip-Till Double Crop 4055 a 4082 a 4869 a 2508 a Convent. Till Double Crop 4237 a 4170 a 4808 a 2562 a a Data pooled over rep. Means within a column followed by the same lowercase letter are not significantly different at P=0.05.

40 30 Table 3.2. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Tifton, GA 2009 and Location Years Tifton 2009 Tifton 2011 Pod Yield Grade TSWV Pod Yield Grade TSWV Cropping System a (TSMK b ) (TSMK b ) kg/ha % kg/ha % Narrow-Tramline Relay 3489 d 72 cd 15 b 3630 c 68 bc 2 cd Wide-Tramline Relay 3707 cd 72 cd 11 c 3770 c 69 ab 1 d Strip-Till Wheat Cover 5093 b 73 c 18 ab 4619 b 71 ab 6 a Convent. Till Wheat Cover 4541 bc 71 d 19 a 4900 ab 71 a 4 bc Early Peanut Only 6014 a 76 b 16 ab 4885 ab 71 a 5 ab Strip-Till Double Crop 3964 cd 77 ab 8 dc 5214 a 67 bc 2 cd Convent. Till Double Crop 3544 d 78 a 7 d 4761 ab 65 c 2 cd Late Peanut Only 4470 bc 78 a 9 dc 5035 ab 68 bc 3 bcd a Data pooled over rep and cultivar. Means within a column followed by the same lowercase letter are not significantly different at P=0.05. b TSMK = total sound mature kernels.

41 31 Table 3.3. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for main plot treatment effects at Plains, GA from Location Years Plains 2010 Plains 2011 Pod Yield Grade TSWV Pod Yield Grade TSWV Cropping System a (TSMK b ) (TSMK b ) kg/ha % kg/ha % Narrow-Tramline Relay 3643 c 67 e 2 c 4051 bc 73 c 6 a Wide-Tramline Relay 3585 c 68 e 2 c 4540 b 74 bc 7 a Strip-Till Wheat Cover 3916 bc 69 d 2 bc 3527 cd 73 c 6 a Convent. Till Wheat Cover 4184 abc 70 dc 4 ab 3064 d 73 c 6 a Early Peanut Only 3982 bc 70 d 5 a 4247 bc 75 ab 8 a Strip-Till Double Crop 4327 abc 73 a 2 c 4816 ab 75 a 3 b Convent. Till Double Crop 4701 ab 71 bc 3 abc 4871 ab 76 a 3 b Late Peanut Only 4907 a 72 ab 3 bc 5670 a 76 a 3 b a Data pooled over rep and cultivar. Means within a column followed by the same lowercase letter are not significantly different at P=0.05. b TSMK = total sound mature kernels.

42 32 Table 3.4. Peanut yield, grade, and tomato spotted wilt virus (TSWV) incidence for sub plot treatment effects at Tifton and Plains, GA from Location Years Peanut Genotype a Pod Yield Grade TSWV (TSMK b ) kg/ha % Tifton 2009 Georgia Green 3944 b 74 c 18 a Georgia-06G 4468 a 76 a 10 b Tifguard 4644 a 74 b 9 b Plains 2010 Georgia Green 3851 b 70 b 4 a Georgia-06G 4455 a 71 a 2 b Tifguard 4164 a 69 b 2 b Plains 2011 Georgia Green 4191 b 75 b 6 a Georgia-06G 5073 a 76 a 5 a Tifguard 3779 b 73 c 5 a Tifton 2011 Georgia Green 4198 c 70 a 6 a Georgia-06G 4623 b 68 b 2 b Tifguard 4982 a 68 b 2 b a Data pooled over main plot treatment and rep. Means within a column followed by the same lowercase letter are not significantly different at P=0.05 b TSMK = total sound mature kernels.

43 33 Table 3.5. Percent visual weed control for main plot treatment effects at Tifton, GA in Weed Type Smallflower Crowfootgrass Goosegrass Cropping System a Morningglory % Control Narrow-Tramline Relay 70 c 65 b 90 ab Wide-Tramline Relay 87 b 54 c 84 b Strip-Till Wheat Cover 99 ab 98 a 99 a Convent. Till Wheat Cover 98 ab 99 a 99 a Early Peanut Only 99 a 99 a 99 a Strip-Till Double Crop 99 a 95 a 98 a Convent. Till Double Crop 99 a 99 a 98 ab Late Peanut Only 99 a 98 a 99 a a Data pooled over rep and cultivar. Means within a column followed by the same lowercase letter are not significantly different at P=0.05.

44 34 Table 3.6. Income above variable cost ($/ha) for main plot treatment effects at Tifton and Plains, GA from Location Years Cropping System a Tifton 2009 Plains 2010 Plains 2011 Tifton 2011 Average $/ha Narrow-Tramline Relay 629 cd 626 cd 1059 bc 408 d 680 Wide-Tramline Relay 462 d 704 cd 1210 b 528 cd 726 Strip-Till Wheat Cover 1111 bc 431 d 306 d 788 bc 659 Convent. Till Wheat Cover 744 cd 521 d 36 d 1039 ab 585 Early Peanut Only 1671 a 512 d 741 c 976 b 975 Strip-Till Double Crop 1317 ab 1398 ab 1875 a 1360 a 1487 Convent. Till Double Crop 1007 bc 1524 a 1850 a 938 b 1330 Late Peanut Only 952 bcd 998 bc 1475 ab 1079 ab 1126 a Data pooled over rep and cultivar. Means within a column followed by the same lowercase letter are not significantly different at P=0.05.

45 Fig Narrow-tramline relay-intercrop. 35

46 Fig Wide-tramline relay-intercrop. 36

47 Fig Damage to wheat from planting procedure in relay-intercrop 37