Nematode Management in Strawberries 1

Transcription

1 ENY J. W. Noling 2 The sting nematode, Belonolaimus longicaudatus, is a pest of major importance to commercial strawberry production in Florida. Although the disease was first noticed in strawberry in 1946, it was not until 1950 that the problem was correctly identified as that of the sting nematode. The increasing importance of sting nematode on strawberry in central Florida was observed to coincide with a decrease in the use of velvet bean as a summer cover crop and an increase in the use of sesbania. During World War II, many strawberry fields that were not cover cropped were more or less neglected and allowed to revert to native weed cover during the summer off-season. It was then observed that the extent to which a fall-planted strawberry crop was injured by sting nematode was strongly influenced by the kind of vegetation that was allowed to grow within the field during the preceding summer. The effect was so pronounced, in fact, that spots of severely stunted plants could be directly related to the different but specific weed plants within the field during summer. A large majority of this natural weed growth was reported as crabgrass, an excellent host for sting nematode (Figure 1). Since the 1950s, B. longicaudatus has subsequently become recognized as one of the most economically important nematode crop pests in the southeastern United States and the primary nematode parasite on strawberry in Florida. The introduction of irrigation into Florida agriculture is thought to have substantially increased cropping problems because of this nematode, especially in strawberry Figure 1. The establishment of crabgrass (Digitaria spp.) in a cover cropped field of hairy indigo (Indigo hirsuta). production. Based on evidence from other crops, parasitism by B. longicaudatus has also been shown to interact with other soilborne pests, causing a greater incidence and severity of certain fungal diseases, most notably Fusarium and Phythium. The sting nematode appears to be a native pest of the sandy soils of the lower Coastal Plains of the southeastern United States. It has such a preference for sandy soils that it fails to exist in significant numbers in soils containing even small amounts of silt, clay, or organic matter content. Sting nematode reproduction is greatest in sandy soil, at temperatures of F (25 30 C) with constant, but moderate, moisture levels. Under suitable conditions, a life cycle is completed in about 28 days. The higher numbers and greater distribution of sting nematode in Florida are probably not only related to the predominance of fine sandy 1. This document is ENY-031, one of a series of the Entomology and Nematology Department, UF/IFAS Extension. Original publication date March Revised December December Visit the EDIS website at 2. J. W. Noling, professor, Entomology and Nematology Department, Citrus Research and Education Center; UF/IFAS Extension, Lake Alfred, FL The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county s UF/IFAS Extension office. U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.

2 soil but also due to the warm subtropical environment. In addition, sting nematode appears to be very sensitive to sudden changes in soil conditions such as rapid drying. Symptoms Strawberry production problems caused by sting nematode tend to occur in more or less definite areas where transplants fail to grow normally (Figure 2). Infested areas consist of spots that vary in size and shape, but the boundary between diseased and healthy plants usually is fairly well defined. Initially a field may have only a few such areas, which may then increase in size and number until the entire field becomes involved. The effect on strawberries is to cause both stunting and decline, the intensity of which is related to initial population level and the rates to which populations increase during the course of strawberry crop growth. Affected plants become semi-dormant, with little or no new growth. Leaf edges turn brown, progressing or expanding from the edges to midrib to include the entire leaf. Leaves seldom become chlorotic, although cases have been reported in which leaf yellowing occurs when essential nutrients are present in limited supply. When chlorosis occurs it is usually at the end of the season when soil temperature and sting nematode populations are increasing and plant demands for water and nutrients are greatest. Since the outer older leaves die first, the plant gradually decreases in size and eventually may be killed (Figure 3). Figure 3. Progressive decline of strawberry due to sting nematode, Belonolaimus longicaudatus. Note death of leaves from outside in towards the crown (oldest to youngest leaves). common where sting nematodes have caused only minor root system damage in the upper 3 to 4 inches of soil. In this soil zone, plants can develop a dense root system but no roots are able to penetrate below this upper layer (Figure 4). Such plants can be easily lifted or pulled from soil and are much more susceptible to droughty conditions and injury from fertilizer salt accumulations. Figure 2. Strawberry plant stunting caused by the sting nematode (Belonolaimus longicaudatus). Note irregular or patchy field distribution of stunted plants rather than throughout the entire field. Sting nematode can be very damaging to nursery seedlings and transplants. As a general rule, most other crop plants are not killed unless subjected to other adverse conditions, but affected strawberry plants undergo progressive decline and may eventually die. Older plants that have already developed an extensive root system can still be severely affected. Under field conditions in Florida, instances are Figure 4. Sting nematode, Belonolaimus longicaudatus, induced symptoms on strawberry roots. Note short, dark and discolored abbreviated roots with swollen root tips. Root growth abnormalities are caused, in part, by injury inflicted at the root tips, which results in little or no new root growth, plants lacking in fine feeder roots, and the development of short stubby branches. Root tips are killed, forcing the development of new lateral roots whose root 2

3 tips in turn are killed. This results in the production of a root system consisting of coarse roots with knobby tips. In addition, necrotic lesions may also be produced laterally along the sides of roots. Because sting nematode does not feed internally, the usual microscopic examination of diseased roots does not aid diagnosis since no organism is present within roots. Positive confirmation of sting nematode can only be made by soil examination. Figure 5. The collection of soil samples for nematode analysis can be acquired from the field using either cylindrical sampling tubes, trowels, bucket auger, or shovel. Casual Organism The original description of the genus Belonolaimus, the type species B. gracilis, and the common name sting nematode was given by Steiner in Much of the early published research works in Florida strawberries reported involvement by B. gracilis. Unfortunately, only the species B. longicaudatus, described by Rau in 1958, has been reported to cause serious injury to a wide array of economically important crops, including strawberries, within the southeastern United States. Because Steiner s B. gracilis has not been observed since the original description, except for one unrecorded observation, the sting nematode associated with strawberry is now generally regarded exclusively to be that of B. longicaudatus. Morphologically, the sting nematode is identified by its unusually long, slender body (2mm) and stylet (generally in excess of 100um). Both males and females are generally numerous within the population. Females possess two ovaries, an esophagus, and overlapping glands; and males are characterized by long, pointed tails, with well developed burse. A number of physiological races have been observed based on differences in morphology and host ranges between geographic populations of sting nematode. Field Diagnosis and Sampling Because of their microscopic size and irregular field distribution, soil and root tissue samples are usually required to determine whether sting nematodes are causing poor crop growth or to determine the need for nematode management. For sting nematodes, sampling and management are a preplant or postharvest consideration because if a problem develops in a newly planted crop there are currently no postplant corrective measures available to rectify the problem completely once the nematode becomes established. Nematode density and distribution within a field must therefore be accurately determined before planting, guaranteeing that a representative sample is collected from the field. Advisory or Predictive Sample (Prior to Planting) Samples taken to predict the risk of sting nematode injury to a newly planted strawberry crop must be taken well in advance of planting to allow for sample analysis and treatment periods if so required. For best results, sample for nematodes at the end of the growing season, before crop destruction, when nematodes are most numerous and easiest to detect. Collect soil and root samples from locations within the field using a cylindrical sampling tube, or, if unavailable, a trowel or shovel (Figure 5). Since sting nematodes are concentrated in the crop rooting zone, samples should be collected to a soil depth of at least 6 10 inches. Sting and root-knot nematode (Meloidogyne hapla) can be deeply distributed throughout the soil profile (48 inches), well below the typical sampling depth and zones of root growth, and have the capability to move upward to infest plant roots. In this scenario, samples procured from surface soil horizons may not adequately describe nematode populations and potential threats to crop growth and yield. As a practical matter however, sample in a regular pattern over the area, emphasizing removal of samples across rows rather than along rows (Figure 6). One sample should represent no more than 5 acres for such a high value crop as strawberries. Fields that have had different crops during the past season or which have obvious differences either in soil type or previous history of cropping problems should be sampled separately. Sample only when soil moisture is appropriate for working the field, avoiding extremely dry or wet soil conditions. 3

4 For diagnostic purposes on established plants, roots and soil cores should be removed to a depth of 6 10 inches from suspect plants. Avoid dead or dying plants, since dead or decomposing roots will often harbor few nematodes. For seedlings or young transplants, excavation of individual plants may be required to ensure sufficient quantities of infested roots and soil. Submission of additional samples from adjacent areas of good growth should also be considered for comparative purposes (Figure 7). Figure 6. Suggested pattern for collecting preplant soil samples for nematode analysis based on compositing soil from field locations. For either type of sample, once all soil cores or samples are collected, the entire sample should then be mixed thoroughly but carefully, and a 1 to 2 pint subsample removed to an appropriately labeled plastic bag. Remember to include sufficient feeder roots. The plastic bag will prevent drying of the sample and guarantee an intact sample upon arrival at the laboratory. Never subject the sample(s) to overheating, freezing, drying, or to prolonged periods of direct sunlight. Samples should always be submitted immediately to a commercial laboratory or to the University of Florida Nematode Assay laboratory for analysis. If sample submission is delayed then temporary refrigerated storage at temperatures of F is recommended. Host Range and Damage B. longicaudatus has a very wide host range including a variety of wild and commercially cultivated plants. Many different small grain and forage crops, fruits, ornamentals, and turfgrasses have all proved to be suitable hosts for sting nematode (Table 1). Most vegetable crops grown in Florida are damaged by and host the sting nematode (Table 1). Cucumber and okra are symptomless hosts but support sting nematode reproduction. Tobacco and watermelon are poor hosts, showing little or no evidence of damage in the field to sting nematode. Figure 7. Suggested strategy for collecting post-plant soil samples for nematode analysis comparing sampling results from areas of good and poor plant growth. The degree of damage expressed in the field depends upon soil population levels which in themselves depend on the preceding crop or natural vegetative cover grown on the land during the summer prior to crop planting. Many weeds serve as good hosts (Table 1). Bermuda and crabgrass, which have been previously implicated as native plants supporting nematode, carry over during the summer and have even allowed population increase. It should be recognized that populations of B. longicaudatus collected from different areas of Florida and from different hosts may produce differing reactions to certain hosts. Differences in reaction include 1) the plants they are capable of attacking, 2) the damage inflicted, and 3) the reproductive output of sting nematode on these crops. Based on this variability, it would be advisable to test use of these plants on a small scale against local populations to determine host status and crop susceptibility before implementing new cropping strategies on a broad scale. General Management Considerations Nematode management should be viewed first and foremost as a year-round, programmatic activity requiring consideration of all cultural, chemical, and agronomic practices within the areas where strawberry plants will be grown. Because strawberry must be vegetatively propagated and transplanted into the field, growers must first pay special attention to the source of strawberry transplants to ensure they are not infested with nematodes. Growers should use only the best quality transplants available and should if possible make special effort to inspect sources of strawberry transplants prior to planting in the field. For example, the northern root-knot nematode, Meloidogyne hapla, can significantly reduce strawberry growth and yield of strawberry, and has been periodically observed on 4

5 infested bare-root strawberry transplants from Canada. After final harvest, the crop should be destroyed as quickly as possible to remove nematode food sources (Figure 8). In most cases, delays in crop destruction contribute to greater nematode population increase and greater difficulty in achieving nematode control. and hairy indigo (Indigofera hirsuta), are vigorous growing legumes and excellent soil building crops that suppress sting nematode and to be resistant to several Meloidogyne spp. Velvet bean (Mucuna deeringiana), another vigorous growing legume, was also observed to suppress sting and root-knot populations in field demonstration trials. Sorghum Sudangrass is a poor choice for a summer rotation on land infested with the sting nematode. Iron clay pea, once widely used as a summer cover crop in the major strawberry producing areas of Florida, was recently shown to support sting nematode reproduction. To be effective, cover crop stands should be established quickly and kept as free as possible of grasses and other undesirable host weeds (Figure 9). Figure 8. Use of early crop destruction with drip fumigation as a nematode management tool in strawberry. Plant Resistance At present there are no nematode resistant strawberry varieties that can be used to manage sting nematode reproduction and yield loss. Based on preliminary observation, some expression of tolerance in the cultivar Sanibel has been observed in the field in which strawberry plants grow and produce fruit but appear to be damaged less than susceptible varieties. Fallowing Although specific time periods have not been quantified, field observations indicate that in the absence of a host, sting nematode will not persist in soil for a long period. Fallowing for even short durations, therefore, particularly when coupled with early crop destruction, generally gives significant and immediate reduction in total nematode population densities in soil. To extend the fallow period, frequent tillage of the field may be required to maintain a clean, weed-free, fallow soil condition. The fact that soil type and soil organic matter content can also dramatically affect population levels indicates that use of soil amendments might prove useful for control. Crop Rotation-Cover Cropping As an alternative to summer fallowing, crop rotation with a poor or nonhost crop can be another effective means for reducing soil populations of sting nematode. Cover crop rotations with sunn hemp (Crotalaria juncea), American jointvetch, hairy indigo, or showy crotalaria have all been shown to reduce sting nematode populations. Sunn hemp Figure 9. Rapid and extensive weed recolonization of a cover cropped field. The fact that all populations of sting nematode have such a wide host range, including numerous weeds and grasses, must be considered in developing an effective crop rotation system for nematode management. Tobacco, cucumber, okra, watermelon, and possibly peanut are the only cultivated crops that have been reported as nonhosts to some sting nematode populations. Some care should be exercised, however, because most of these crops, though reported as nonhosts for the sting nematode, are excellent hosts for other nematodes such as Meloidogyne spp. For these rotations to be effective, weed and grass control should be as complete as possible since they can act as excellent carry-over hosts. Once again, crop rotation systems developed for a given geographical area may be of limited value 5

6 in others because some local populations of sting nematode respond differently on different hosts. In this case, small scale grower field evaluations should precede broadscale implementation of a specific crop rotation strategy. Biological Control At present there are no effective, commercially available, biological control agents which can be successfully used to control sting or root-knot nematodes. Chemical Control Nonfumigant Nematicides At present there are no commercially available nonfumigant nematicides registered for use on Florida strawberry. Fumigant Nematicides The sting nematode can be controlled with fumigant nematicides (Table 2, 3). The use of soil fumigants for control of the sting nematode was experimentally first attempted in strawberry in From these trials it was determined that either solid fumigation treatment before bedding or row treatment as the beds were made allowed strawberry growers to produce productive crops of strawberry on land in which sting nematode had been destructive to in previous crops. By 1964, virtually all of the Florida strawberry acreage was being treated with a fumigant nematicide like methyl bromide, which resulted in a four-fold increase in strawberry yields over that of previous nonchemical methods (Figure 10). As indicated, use of broadspectrum fumigants (Table 2) effectively reduces nematode populations and increases strawberry yields, particularly when coupled with other chemical and cultural control practices. Since these products must diffuse through soil as gases to be effective (see Figure 13), the most effective fumigations occur when the soil is well drained, in seedbed condition, and at temperatures above 60 F. Fumigant treatments are most effective in controlling sting and root-knot nematode when residues of the previous crop are either removed or allowed to decay. When plant materials have not been allowed to decay, fumigation treatments may decrease but not eliminate populations of root-knot nematodes in soil, particularly nematodes within the egg stage. Crop residues infested with root-knot nematode may also shelter soil populations to the extent that significantly higher rates of application may be required to achieve nematode control. To avoid these problems, growers are advised to plan crop destruction and soil cultivation practices well in advance of fumigation to insure decomposition of plant materials before attempting to fumigate. Figure 10. Sting nematode, Belonolaimus longicaudatus, induced stunting of strawberry, comparing fumigated and nonfumigated test strips of plant row. Since the introduction of fumigants to Florida strawberry production in early 1960s and with the final phase out of methyl bromide in 2015, many different alternative soil fumigants have been evaluated in field trials to characterize pest control efficacy and crop yield response (Table 2). The results of these research trials have provided basis for overall generalization of pesticidal activity for each of the alternative fumigant chemicals. As a standard for comparison, this research has repeatedly demonstrated methyl bromide to be very effective against a wide range of soilborne pests including nematodes, diseases, and weeds. Chloropicrin has proved very effective against diseases but seldom nematodes or weeds. Telone (1, 3-dichloropropene) is an excellent nematicide but generally performs poorly against weeds and diseases. Bacterial pathogens have not been satisfactorily controlled by any of the fumigants. Metam sodium and metam potassium can provide good control of weeds, nematodes, and disease when placed properly in the bed, however, research to evaluate modification of rate, placement, and improved application technology have not resolved all problems of inconsistent pest control. Dimethyl disulfide (DMDS), the newest entry to registered fumigants in Florida, has demonstrated good to excellent control of nematodes, disease, and weeds when coapplied with chloropicrin. Allyl isothiocyanate (AITC) (Dominus), the newest fumigant entry to be registered in Florida, has shown some promise for broad-spectrum control of nematode, disease, and weeds, but is still in 6

7 comprehensive assessment to evaluate its relative pesticidal activity. As indicated previously, the complete phaseout of methyl bromide in the United States beginning in 2005 created a significant void for us in the chemical arsenal then used for soilborne pest and disease control in Florida strawberry. This fact is still made quite clear from a review of recent field research trials conducted in Florida, which shows that no single, equivalent replacement (chemical or nonchemical) currently exists that exactly matches the broadspectrum efficacy of methyl bromide. In preparation for the complete phase-out and loss of methyl bromide in 2015, university research programs within Florida have continued to identify and evaluate more robust strategies which minimize cropping system impacts, accounting for a diverse range of pest pressures and environmental conditions. Based on summary and comparison of methyl bromide alternative chemical trial results in Florida, much of the current field research continues to focus on evaluations of chloropicrin co-applied with additional fumigants. In this co-application approach, chloropicrin has clearly been shown to be an integral, foundational component of any alternative chemical approach to replace methyl bromide. Of the chloropicrin combinations, only Telone C-35, a combination of 1,3-dichloropropene with 35% chloropicrin, have been the most extensively evaluated in Florida strawberry field trials since Dimethyl disulfide (DMDS) in combination with chloropicrin (21%), the newest registered fumigant in Florida, has not been as extensively studied but has proven effective for soilborne pest and disease control in central and south Florida field trials. Coupling use of DMDS with totally impermeable mulch films (TIF), a new mandatory requirement for its use in Florida, has helped to resolve odor issues associated with its use, but has increased production costs accordingly. Allyl isothiocyanate, the newest registered fumigant in Florida, has looked promising in preliminary trials but it has not been as extensively studied and, as such, should be considered still in assessment. In general, this research has demonstrated that Telone C35, applied in combination with a separately applied herbicide or fumigant product for weed control, has been identified as the best chemical alternative replacement for methyl bromide for strawberry production in Florida. Recent research on soil application technologies in Florida and Georgia have demonstrated improved weed control with metam sodium or potassium applied through a series of minicoulters to the established plant bed just before installation of the plastic mulch. This has also been demonstrated in large scale, commercial field trials around the state. In many of these studies, use of other alternative fumigants such as Pic Clor 60 (a formulation with 60% chloropicrin) in combination with a herbicide and or additional fumigant treatment, have not consistently produced the same near equivalent yields to that of methyl bromide or Telone C35 in the presence of high sting nematode pest pressures. Under conditions of high pest pressures (nematodes, disease), Telone C35 coupled with other IPM practices might also be required and combined to achieve adequate nematode control and economic crop productivity. Drip Fumigation Drip fumigation is defined simply as the application of a soil fumigant through a drip irrigation system. Some soil fumigants, like Vapam (metam sodium) and K-Pam (metam potassium), are readily soluble in water and can be applied directly into irrigation water, while others require special emulsified concentrate (EC) formulations for application (Table 3). For example, chloropicrin and Telone (1,3-dichloropropene or 1,3-D) are not highly soluble in water and must be premixed with special emulsifying agents to enhance solubility in water and to promote the uniform suspension of the fumigant in water before delivery into the irrigation lines. Considerable research is currently underway to optimize application technologies to improve performance consistency with drip applied fumigants. In Florida, drip applied Pic Clor 60 EC or Telone Inline (mixtures of 1,3-D and chloropicrin with an emulsifying agent) have provided satisfactory soil borne pest control and of strawberry crop yields. Currently, as much as 40 to 50% of the Florida strawberry acreage is thought to be drip fumigated with a fumigant product such as Vapam, Kpam, Pic EC, Pic Clor 60EC, Telone Inline, DMDS+PIC EC, or AITC (Dominus). In recent years, a number of Florida research trials have also demonstrated the value of drip treatments both as crop termination treatments in the spring and as preplant treatments in the fall under new or old, double-cropped plastic. The spring applied drip fumigation treatments were particularly effective for reducing end of cropping season nematode populations that had built to high levels and for eliminating food sources for nematodes to use for continued reproduction and population growth. Safe and effective drip fumigation requires an understanding of how different physical, chemical, and environmental factors affect water and gas phase movement of the different soil fumigants. Additionally, it requires new chemical injection equipment with proper safety devices, a leak-free drip irrigation system with uniform water distribution, and fumigant application and dilution into the proper amount of water. 7

8 A significant amount of research has been conducted to characterize the dynamics of drip irrigation water movement and use of the drip system for fumigant chemical delivery. These studies have relied upon tracking the movement and spatial distribution of water soluble colored dye, introduced into the irrigation stream. Movement of water-borne dye and fumigant has been investigated for varying injection periods and total water volumes, drip tube numbers per bed, flow rates, emitter spacings, soil compaction regimes, and bed dimensions. The overall results of these studies, as well as generalized summary of field results of drip fumigation trials, form the basis for the following recommendations for maximizing water phase movement of all drip applied soil fumigants, such as Vapam, K-Pam, Pic Clor 60EC, AITC, and Inline. In general, the results of all of the previous dye studies have repeatedly shown that the average width, depth, and crosssectional area of the wetted zone generally increases with irrigation water volume, typically forming a hemispherical shape until water fronts from adjacent emitters along the drip tape collide. As these fronts collide, a wetted strip of no more than 12 to 15 inches develops parallel to the drip line. Measured laterally from the drip emitter, outward water movement was seldom measured to be more than 6 to 7 inches. Depending on the width of the bed, these studies demonstrated that it was virtually impossible to wet more than 40 to 60% of the raised plant bed with a single drip tube. With two drip tapes, it was possible to wet from 75 to 95 percent of the bed. In general, the wetting front is typically two- to three-fold greater with use of two drip tubes rather than with a single tube per bed. But even with two tapes per bed, it is always more difficult to wet a high proportion of a wide bed compared to a narrow bed. For a given water volume, the use of two tapes per bed increased spatial distribution of irrigation water simply because of the spacing between drip tubes and the increased number of emission points along the bed. In the overall analysis of the relationship between total irrigation water volume and spatial distribution of the wetted zone, it appears that most bed wetting occurs in the time to deliver the first 300 gallons of water per 100 linear feet of row. If a maximum depth of inches from the top of the bed is assumed, then irrigation run times required to deliver water volumes of 100 to 200 gallons per 100 feet of row should not be exceeded so as to contain the wetting front within the future rooting zone of the plant. In general, reduced effectiveness and consistency can be observed with any fumigant product when applied through a single drip tape per bed. Increasing rates of applications have helped to overcome this problem, but oftentimes not entirely. Previous research has also demonstrated that fumigant concentrations (and their efficacy) could be enhanced across the bed by using highly retentive mulches, such as virtually impermeable films (VIF) or metalized mulches. Fumigants under these mulches are prolonged at higher concentrations which results in higher overall exposure to lethal concentrations and improved lateral spread of the fumigant across the bed. Before considering drip fumigation as a pest management tool, an evaluation of irrigation system design, and distribution uniformity should be conducted to ensure water distribution and operating pressure uniformity, and thus drip emitter discharge rates within the field and entire length of row. Any inconsistency in drip flow will be reflected in variability in fumigation rates, pest control efficacy, and strawberry crop yield response. Until 2005, methyl bromide was used almost exclusively for soilborne nematode, weed, and disease control (Figure 11). Methyl bromide was completely phased out of production and use within the United States on January 1, Now that methyl bromide is no longer available, alternative chemical control options involve individual or combined treatments of other federally registered fumigants (Table 2). Use of these broad-spectrum fumigants has also been shown to effectively reduce nematode populations and to increase strawberry yields, particularly when compared with other biological, biorational, and nonchemical management approaches. Figure 11. Preplant soil fumigation for nematode control. Nonchemical Approaches The breadth and focus of the methyl bromide alternatives research program in Florida has not been limited exclusively to evaluation of chemical combination treatment regimes. The program also encompasses an evaluation of a diversity of nonchemical tactics. Since 1993, an ever expanding list of nonchemical alternatives has been evaluated in field research and demonstration trials. Some of the nonchemical alternatives evaluated include 8

9 1) summer cover crops; 2) pest-resistant crop varieties; 3) organic amendments; 4) solarization; 5) biological control agents; 6) natural product pesticides; 7) super-heated water and steam; 8) fallowing; and 9) paper and plastic mulch technologies and emissions reduction. In general, the results from some of these nonchemical studies have been encouraging, but, in most cases, should be construed as incomplete from a soil pest control or crop yield enhancement perspective. Many of these nonchemical tactics are not only marginally effective (at this time) or show activity against a single target pest, but also impractical, cost prohibitive, or have requirements for specialized equipment and operators. In addition, none of the nonchemical tactics should be considered standalone replacement strategies for soil fumigation at this time. As a result, new field studies evaluating combinations of tactics have been proposed or are in progress to establish cumulative impacts on soilborne pest control and crop yields. Summary In summary, nematode control measures can be conveniently divided into two major categories including cultural and chemical control measures. None of these measures should be relied upon exclusively for nematode management. Rather, when practical and economics permit, each management procedure should be considered for use in conjunction with all other available measures for nematode control and used in an integrated program of nematode management. In addition to nematodes, many other pests can cause crop damage and yield losses that further enforce the development of an overall Integrated Pest Management (IPM) program, utilizing all available chemical and nonchemical means of reducing pest populations to subeconomic levels. An IPM approach further requires that growers attempt to monitor or scout fields for pest densities at critical periods of crop growth. Regardless of product, effective use of any soil fumigant for nematode control requires appropriate soil preparation and conditions prior to treatment. If a fumigant is to be used, begin field preparations 6 to 8 weeks ahead of planting so that crop debris will be completely decayed (Figure 12). Since all fumigants must diffuse through soil as gases to be effective (Figure 13), the most efficient fumigations occur when the soil is well drained, in seedbed condition, and at a temperature above 60 F. Because all of the fumigants are toxic to living plants, an appropriate planting delay of 1 to 3 weeks to aerate the soil must also be observed to avoid crop injury due to phytotoxic soil residues. Nematodes are very important economic pests in Florida strawberry, estimated to occur on as much as 40% of Florida strawberry acreage. The most important nematode pest is the sting nematode, and occassionally root-knot when introduced within bare-root transplants from Canadian nurseries. Strawberries are typically produced on plastic-mulched beds in most areas of Florida. These beds are routinely fumigated with a multi-purpose fumigant (Table 1) at the time they are covered for broad spectrum soil pest control. Several brands of the fumigants used most widely for strawberry, including many different Telone/chloropicrin mixtures as well as metam sodium and potassium. There is more than ample research evidence to show that some formulations of Telone and chloropicrin are better suited for sting nematode control (e.g., Telone C35). Other formulations (e.g., Pic Clor 60) may be more effectively used when specific disease complexes (i.e., combinations of diseases) are the principal problems to be resolved in the field. In this regard, it is the grower who must determine which pests should be expected to be encountered in the field, and who must check the label of the fumigant product to be used to be sure that it is being applied according to label instruction. During the past several years, all of the fumigants labels have changed significantly to protect handlers in the field and residents and bystanders in close proximity of the field. Certified Figure 12. Field tillage operation as a prerequisite to soil fumigation. applicators are strongly encouraged to review product label details for additional use restrictions based on soil characteristics, buffer zones, requirements for Personal Protective Equipment (PPE), mandatory good agricultural practices (GAPs), product training certification, and rate modifying recommendations with use of highly retentive mulch films. 9

10 Figure 13. Nematode as aquatic organisms encountering both liquid and gas phase nematicides in soil. Table 1. Host status to sting nematode, Belonolaimus longicaudatus, to various turf, forage fruit, vegetable, and agronomic crops. Bluegrass Bentgrass Centipedegrass St. Augustine Bahia Bermuda Pangola grass Beans Carrots Celery Sweet corn Cowpea Eggplant Onion* Pea Citrus* Sesbania Sorghum/Sudan grass Iron Clay pea Crabgrass Bermuda Fescues All members of grass family Fescue Corn Oats Millet Rye Wheat Peanut* Strawberry* Cabbage* Cantaloupe Cauliflower Endive Lettuce Tomato Turnip Eggplant Mungbean Pigeonpea Good Hosts Lambsquarter* Cudweed Dogfennel Johnsongrass Turf, Field, and Forage Crops Clovers Cotton Soybean Barley Lespedeza Fruit and Vegetable Crops Cover Crops Okra* Cucumber* Snap bean Squash Pepper Sweet potato* Potato Hairy vetch Joint vetch Common Weeds *Variable host response to geographic/physiologic races of sting nematode. Beggarweed Ragweed Wild carrot Spanish needle Tobacco Watermelon* Asparagus Hot pepper Sunn Hemp Hairy Indigo Crotalaria Velvet bean* Poor or Nonhost Bidens Horseweed Buckhorn plantain Pokeweed Sandbur Cocklebur* Jimson weed Sorrel Wild garlic Jerusalem oak 10

11 Table 2. Generalized summary of maximum use rate and relative effectiveness of various soil fumigant alternatives to methyl bromide for nematode, soilborne disease, and weed control in Florida. FUMIGANT CHEMICAL 1 Maximum Use Relative Pesticidal Activity Nematode Disease Weed 1) Chloropicrin lb None to Poor Excellent Poor 2) Metam Sodium 75 gal Good to Poor Good to Poor Good to Poor 3) Telone II 18 gal Good to Excellent None to Poor Poor 4) Telone C17 26 gal Good to Excellent Good Poor 5) Telone C35 35 gal Good to Excellent Good to Excellent Poor to Fair 6) Pic-Clor lb Good to Excellent Good to Excellent Poor to Fair 7) Metam Potassium 60 gal Good to Poor Good to Poor Good to Poor 8) Dimethyl Disulfide 2 53 gal Good to Excellent Good to Excellent Poor to Excellent 9) AITC (Dominus) 40 gal Still in assessment Still in assessment Still in assessment 1 Use of soil fumigants in Florida now requires new fumigant product and applicator training certifications, personal protective equipment, buffer zones, mandatory good application practices, and other new restrictions and requirements. 2 Broad spectrum pest control achieved when coapplied with chloropicrin (21% wt/wt). Provides excellent control of nutsedge but poor to fair control of annual grasses and requires the use of a herbicide for adequate control. Rates are believed to be correct for products named, and similar products of other brand names, when applied to mineral soils. Higher rates are required for muck (organic) soils. However, the grower has the final responsibility to see that each product is used legally; read the label of the product to be sure that you are using it properly. Table 3. Non-fumigant nematicides for strawberries in Florida. Product Nimitz Application Information All applications to okra must be incorporated either physically or via drip or overhead irrigation. Make preplant applications at a rate of 3.5 to 7 pints, (56.0 to fl. oz.) per acre, a minimum of seven days before planting. Do not plant any unlisted crops into treated land for 365 days after application of the product. Do not apply more than one application per crop, and no more than 112 fl. oz. of product per acre, per year (365 days). Provides control only for nematodes and provides no residual control. Product is commercially available but is still actively under assessment in field trial evaluations. Nonfumigant nematicide type products are generally not thought to be as consistently effective against root nematodes as the fumigants, but they are registered as indicated. 11

12 Table 4. Fumigant nematicides for strawberries in Florida. Nematicide Broadcast application 1 In-the-row applications Gallons or Lbs Per acre Fl oz /1000 ft / chisel spaced 12 apart Telone II 2,3 27 to 35 gal 79 to 102 For any row spacing, application rates given may be concentrated in the row, but shall Telone EC 2,3 never exceed the labeled maximum for broadcast applications. Consult the product label for additional detail. Telone C-17 2, to 42 gal 95 to 123 For any row spacing, application rates given may be concentrated in the row, but shall never exceed the labeled maximum for broadcast applications. Consult the product label for additional detail. Telone C-35 2,3 39 to 50 gal 114 to 146 For any row spacing, application rates given may be concentrated in the row, but shall never exceed labeled maximum for broadcast applications. Consult the product label for additional detail. Telone InLine 2,3 29 to 56 gal - For drip fumigation, consult the product label for overall rate, drip concentration, and flow modifying application directions. Pic Clor 60 2, gal 57 to 90 Consult product label for overall rate and chisel flow modifying application directions. Pic Clor gal - For drip fumigation, consult product label for proportionately reduced overall rates, drip 60 EC 2,3 concentration, and drip flow modifying directions and procedures. Vapam HL 75 gal - For drip fumigation and crop termination, consult product label for proportionately reduced overall rates, drip concentration, and flow modifying directions and procedures. KPam HL 60 gal - For drip fumigation and crop termination, consult product label for proportionately reduced overall rates, drip concentration and flow modifying directions. Dimethyl Disulfide (DMDS) gal - Compared to broadcast application, apply proportionately less for in the row applications based on the ratio of bed width to row spacing. Consult the product label for additional detail and rate modifying recommendation and mandatory requirements for totally impermeable mulch films (TIF). Allyl Isothiocyanate (AITC) Dominus 40 gal - For drip or in-row fumigation and crop termination, consult product label for overall rates, drip concentration, and flow modifying directions. 1 Gallons /acre and Fl oz / 1000 feet provided only for mineral soils. Higher rates may be possible for heavier textured (loam, silt, clay) or highly organic soils. 2 All of the fumigants mentioned are for retail sale and use only by state certified applicators or persons under their direct supervision. New supplemental labeling for the Telone products must be in the hands of the user at the time of application. See label details for additional use restrictions based on soil characteristics, buffer zones, requirements for Personal Protective Equipment (PPE), mandatory good agricultural practices (GAPs), product and applicator training certification, and rate modifying recommendations with use of highly retentive Totally Impermeable mulch films (TIF). 3 Higher application rates are possible in the presence of cyst-forming nematodes. Rates are believed to be correct for products named, and similar products of other brand names, when applied to mineral soils. Higher rates are required for muck (organic) soils. However, the grower has the final responsibility to see that each product is used legally; read the label of the product to be sure that you are using it properly. 12