1. Foundation herbicide programs for Roundup Ready soybeans

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1 Number 141 May 27, Foundation herbicide programs for Roundup Ready soybeans 1 2. Results of 2007 fungicide trials on corn 2 3. Assessing early-season hail damage on corn 6 4. Effect of stand loss on corn yields 7 1. Foundation herbicide programs for Roundup Ready soybeans One of the management practices producers can use to help prevent the development of glyphosate-resistant weeds is to use herbicides with different modes of action, either as a sequential treatment in the same crop year or as a tankmix with glyphosate. As far as glyphosate-resistant weed populations currently in Kansas, marestail probably is the most widespread problem. Glyphosate-resistant waterhemp and giant ragweed also have been confirmed and are a concern in Kansas. Although it hasn t been confirmed in Kansas, the development of glyphosate resistant Palmer amaranth is also a major concern, since Palmer amaranth is a major weed problem in Kansas and glyphosate resistant Palmer amaranth has been documented in the southeast U.S. When applying glyphosate on stubble fields and fallow ground or as a burndown prior to planting, it is always a good idea to add some 2,4-D or dicamba in with the glyphosate for burndown treatments. With the low cost of glyphosate, it has been tempting to increase the glyphosate rate and eliminate the 2,4-D or dicamba because of fewer drift and preplant interval concerns. However, adding 2,4-D or dicamba makes good sense with higher glyphosate prices and the risk of glyphosate reistant weeds. In Roundup Ready soybean fields, there are several tankmix options producers can use with over-the-top applications of glyphosate. This may be especially helpful for control of troublesome weeds, such as marestail and morningglory. Where glyphosate-resistant marestail is a problem, producers can improve control by adding 0.3 oz per acre of FirstRate. Another practice producers can use to add a different herbicide mode of action to their fields of Roundup Ready beans is to apply a preplant or preemerge residual herbicide. This is often called a foundation treatment, and can be very effective in helping prevent 1

2 the development of glyphosate-resistant weeds, as well as providing early season weed control and providing more flexibility with timing of the postermegnece treatments. In many cases, the use of a foundation treatment will eliminate the need for a second postemergence treatment.. There are many preemerge herbicides available for use in soybeans. Here are the broad categories of preemerge herbicide options for soybeans, and their strengths and weaknesses in terms of weed control. * Valor-based herbicides and premixes. (Valor S, Valor LT, Envive, Enlite) -- Strengths: Pigweed, morningglory, velvetleaf control. -- Weaknesses: Timely rainfall needed for activation. Occasional stunting with heavy rains at emergence. * Authority-based herbicides and premixes. (Authority First, Sonic, Authority Assist, Authority MTZ, Spartan) -- Strengths: Pigweed, morningglory, velvetleaf control. -- Weaknesses: Timely rainfall needed for activation. * Acetamide-based herbicides and premixes (Intrro, Dual II Magnum, Prefix, etc.) -- Strengths: Pigweed and grass control. -- Weaknesses: Large-seeded broadleaves such as velvetleaf and cocklebur. * Prowl -- Strengths: Low cost and grass control. -- Weaknesses: Broadleaf weed control. -- Dallas Peterson, Weed Management Specialist dpeterso@ksu.edu 2. Results of 2007 fungicide trials on corn Six fungicide trials on corn were conducted by K-State in The site conditions, hybrids, cropping system, and other factors varied at each site. Hybrid Maturity GLS Rust Previous Crop Meadowlark District (NE Kansas) Stauffer 2677BR 110RM 8 (9=best) Soybean Manhattan Dekalb DKC RM 7 (1=best) 3 (1=best) Soybean Conv. Till Rossville (Irrigated) Dekalb DKC RM 3 (1=best) 5 (1=best) Soybean No-Till Scandia (Irrigated) Pioneer 33B53 113RM 4 (9=best) Soybean No-Till Haviland (Irrigated) Stauffer 2721BR 114RM 6 (9=best) Corn Strip-Till Stevens/ Seward Co. (Irrigated) Garst RM 4 (1=best) Corn Strip-Till 2

3 Population 28,000 Spacing 20 28,800 29,600 30,200 ~28,000 ~30,000 Planted April 30 April 23 May 1 April 23 April 20 April 24 Sprayed July 5 July 2 July 11 July 3 July 6 July 12 Harvested Sept. 10 Sept. 24 Sept. 21 Sept. 26 August 29 Sept. 6 The fungicides used, and rates, also varied. The following table is the key to the treatment abbreviations used in the yield charts below. UTC Untreated Check HL6 Headline 6 oz/acre HL9 Headline 9 oz/acre HL6-NP Headline 6 oz/acre 2 lb N/acre HL4.5-C Headline 4.5 oz/acre Caramba 4.5 oz/acre QU14 Quilt 14 oz/acre ST10 Stratego 10 oz/acre ST12 Stratego 12 oz/acre Meadowlark Rossville Scandia Haviland Stevens/ Seward District Manhattan (Irrigated) (Irrigated) (Irrigated) Co. (Irr.) The fungicides were applied at the VT to R1 stages of growth. 0.25% v/v NIS, 20 gal. water/acre, 35 psi In general, the leaf disease pressure was greatest in the Southwest tests Northeast common rust, gray leaf spot Present at VT or soon after but <5% of leaf area Occupied significant leaf area by late grain fill (R4 early R5) Southwest gray leaf spot More disease during grain fill Good rainfall through early to mid grain fill High humidity all summer favorable for leaf diseases 3

4 Excellent yields at all locations The charts below show the yield responses from fungicide applications at the various locations. Many ratings other than grain yield were also recorded, including disease severity and progression up the plant, lodging, grain moisture, kernel mass, ears per acre, and test 4

5 weight. Without showing all the data, we can summarize them in the following conclusions: Fungicide delayed disease progression and leaf senescence. Fungicide delayed dry-down at Manhattan, and a similar trend was observed in other trials. Fungicide reduced lodging at Manhattan. Fungicide did not affect kernel mass or ear weight. Test weight response to fungicide was inconsistent. Yield differences were not statistically significant at all locations, but: Northeast locations had no consistent response. Leaf diseases occupied <5% of leaf area at silk. Leaf diseases did not move above flag leaf until R4-R5. Southwest locations showed trends for increased yields with fungicides. Haviland ~ 4 to 6 bushel/acre, Stevens County 0 to 13 bushel/acre yield advantage. These locations had greater disease pressure (primarily gray leaf spot) earlier in the grain fill period. It is difficult to make any general recommendations about fungicide use on corn. Fungicide applications are most likely to be needed on corn: * If the hybrid is susceptible or intermediate to gray leaf spot or rust, * In high-residue corn-on-corn cropping systems, * If leaf diseases are present, and * If weather conditions are predicted to be warm and humid. Producers should scout for disease pressure and apply fungicides when needed. A decision making tool for evaluating the potential profitability of fungicide applications for crops has been developed by Kevin Dhuyvetter, Agricultural Economics, and Doug Jardine, Plant Pathology. Go to: Click on Economics of Spraying Soybeans. Despite the title of the spreadsheet, it can be used for corn, wheat, and other crops as well as soybeans. Many individuals were involved in conducting these trials in 2007, including: Farrell Allison (Crop Quest, Inc.) Stu Duncan (Northeast Area Crops and Soils Specialist) Barney Gordon (Agronomist-in-charge, Irrigation Experiment Field, Scandia) David Hallauer (Meadowlark Extension District Agent, Oskaloosa) Mike Hanson (Seward County Extension Agent, Liberal) Mike Hershey (Independent Crop Consultant, Stevens/Seward Counties) Larry Maddux (Agronomist-in-charge, Kansas River Valley Experiment Field, Topeka) Tom Roberts (Stevens County Extension Agent, Hugoton) 5

6 -- Kraig Roozeboom, Crop Production and Cropping Systems Specialist -- Curtis Thompson, Weed Management Specialist (former Southwest Area Crops and Soils Specialist) 3. Assessing early-season hail damage on corn Hail storms are common in Kansas this time of year, causing damage to both maturing wheat and young stands of corn. Wheat injury is easy to diagnose, but diagnosing injury to corn seedlings is more difficult. Hail damage always makes corn look bad, and can make for some sleepless nights. But while the physical damage is apparent, the actual effect on yield is not as obvious. Potential corn yield losses from hail gradually increase as the crop gets more mature, up to the silk stage, when peak yield loss occurs. After silking, yield losses from hail damage normally decline again. Why is that? There are several reasons, and all are based on the growth and development of the corn plant. * Emergence until stem elongation (VE to V5). Up through the 5-leaf stage of growth, the growing point of corn is below the soil surface. At the worst, hail damage would remove all five leaves, but typically not damage the growing point. A corn plant has 24 to 26 leaves at tasseling. If the plant loses five of those leaves early on, it will still have the potential to have 19 to 21 leaves at tasseling. Yield will be reduced, but by much less than one might expect from the appearance of the plant. * Stem elongation to tassel (V6 to VT). The growing point begins extending aboveground by the 6-leaf stage, although it is still protected by several layers of leaves and sheaths. The number of rows that will be in the ear is established by the 12-leaf stage. Stress during V8 to V11 can reduce row number. The number of kernels per row is not determined until about V17, just before tasseling. Hail damage and loss of leaf area during these stages of growth can cause increasing potential for yield loss. Hail can also cause stalk bruising during these stages of growth, but it is hard to determine the amount of damage from stalk bruising until later in the season. * Tassel to maturity (VT to R6). At VT to R1 (tassel to silk), the corn plant is more vulnerable to hail damage than at any other stage. The tassel and all leaves are exposed at that time. No more leaves will be developed, and the corn cannot replace a damaged tassel. Furthermore, the stalk is exposed, with only one layer of leaf sheath protecting it. Unlike wheat, corn cannot fill from the stem if leaves are lost at this stage of growth. The 6

7 six to eight leaves above the ear are the most important, and provide most of the grain fill. The four-week period centered around silking is critical to corn, and not only in regard to hail damage. Drought stress, excessive moisture, extreme heat, diseases, and even high winds can all stress the plant at this critical stage of growth and reduce yields. Early in this period, stress can reduce kernel number by limiting potential ear size. Stress right at silking can reduce the number of kernels fertilized. And stress just after silking can cause fertilized kernels to abort. Leaf Area - Yield Loss Relationships Percent Yield Loss V5 V7 V9 V11 V13 V15 V17-18 Silk Pre-blister Early Milk Late Milk Early Dent Late Dent Mature Percen t Leaf Area Loss Growth Stage Graphic illustrating the relationship between estimated yield loss and percent leaf area loss at different growth stages of corn (based on data from Corn Loss Adjustment Standards Handbook, USDA-FCIC-25080, pp. 7-98). -- Kraig Roozeboom, Crop Production and Cropping Systems Specialist kraig@ksu.edu 4. Effect of stand loss on corn yields Stand loss in corn usually causes relatively little yield loss, at least at populations greater than 24,000. The amount of yield reduction from stand loss depends on the stage of growth. 7

8 Research by Barney Gordon at the North Central Experiment Field evaluated the effect of stand loss on yields, ear number, and ear size by removing plants at various stages of growth. Yield Loss From Three Levels of Stand Loss at Three Growth Stages 100 Percent Yield Loss Emergence V Percent Stand Loss Growth Stage Ear Number At Three Levels of Stand Loss at Three Growth Stages 2.0 Ears Per Plant Emergence V Percent Stand Loss Growth Stage 8

9 Ear Size At Three Levels of Stand Loss at Three Growth Stages 1200 Kernels Per Ear Emergence V Percent Stand Loss Growth Stage This study showed that: * Yield loss was much less than stand loss at every growth stage. * Yield loss increased with stand losses that occurred at later growth stages. * Ear number per plant increased slightly at 50% stand loss, and more at 75% stand loss. * Seed weight did not change as a result of stand loss (data not shown). * Ear size increased with greater stand loss at early stages of growth. When considering replanting due to poor stands, keep in mind that planting corn in early June in much of Kansas can result in yield losses of up to 50% compared to a typical planting date. Based on the data above, it would probably be better to keep an existing stand even with as much as 50% stand loss than to replant in early June. Of course, much depends on the uniformity of the remaining stand and the weather for the rest of the growing season. -- Kraig Roozeboom, Crop Production and Cropping Systems Specialist kraig@ksu.edu These e-updates are a regular weekly item from K-State Extension Agronomy and Steve Watson, Agronomy e-update Editor. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Steve Watson, swatson@ksu.edu, or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader jshroyer@ksu.edu 9