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1.This document is a chapter of SP 214, last printed in 1990 as Circular 98 C. SP 214 ,Tomato Production Guide for Florida, last printed in 1990 as Circular 98 C, is a publication of the Commercial Vegetable Guide Series, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Publication date: August 1997.For more information about how to order the complete print document, SP 21 4, call UF/IFAS Distribution at (352) 392-1764. Please visit the FAIRS Website at http://hammock.ifas.ufl.edu The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide resea rch, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Servi ce office. Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / Christine Taylor Waddill, Dean. 2.J.W. Noling, professor, Citrus-REC, Lake Alfred, Cooperative Extension Service, Institute of Food and Agricultural Sciences (IFAS), University of Florida, Gainesville FL 32611. The Tomato Production Guide for Florida is edited by G.J. Hochmuth, professor, Horticultural Sciences De partment, IFAS. SP 214Tomato Production Guide for Florida: Nematode Control1J.W. Noling2Plant parasitic nematodes, are small microscopic roundworms which live in the soil and attack the roots of tomato plants. Crop production problems induced by nematodes therefore generally occur as a result of root dysfunction, reducing rooting volume and foraging and utilization efficiency of water and nutrients. Many different genera and species of nematodes can be important to crop production in Florida. In many cases a mixed community of plant parasitic nematodes is present in a field, rather than having a single species occurring alone. In general, the most widespread and economically important nematode species include the root-knot ( Meloidogyne spp.), sting (Belonolaimus longicaudatus ) awl ( Dolichodorus spp.) and stubby root ( Trichodorus spp.) nematodes. In rock-based and muck soils, rootknot and reniform (Rotylenchulus spp.) are most important. The host range of these nematodes, as with others, include most if not all of the commercially grown vegetables within the state. Yield reductions can be extensive but vary significantly between plant, producing areas of the state, and nematode species. In addition to nematodes as cause of direct crop damage, many of these species have also been shown to predispose tomato plants to infection by fungal (i.e., Fusarium wilt) or bacterial pathogens or to transmit virus diseases, which contributes to additional yield reductions. Integrated pest management (IPM) for nematodes requires: 1) Determining whether pathogenic nematodes are present within the field; 2) Determining whether nematode population densities are high enough to cause economic loss; and 3) Selecting a profitable management option. Attempts to manage nematodes may be unprofitable unless all of the above IPM procedures are considered and carefully followed. Similarly, some management methods pose risk to people and the environment. Therefore it is important to know that their use is justified by actual conditions in a field.Typical Symptoms Typical symptoms of nematode injury can involve both above ground and below ground plant parts. Foliar symptoms of nematode infestation of roots generally involve stunting and general unthriftiness, premature wilting and slow recovery to improve soil moisture conditions, leaf chlorosis (yellowing), and other symptoms characteristic of nutrient deficiency. In tomato, ethylene production induced by root-knot nematode infection plays a major role in the development of nematode damage
Tomato Production Guide for Florida: Nematode Control Page 2 February 1998symptoms. Other symptoms associated with nematode induced ethylene production include inhibition of plant growth, accelerated plant senescence, and chlorophyll degradation leading to plant chlorosis. Plants exhibiting chlorotic, stunted, or decline symptoms usually occur in patches of nonuniform growth rather than as an overall decline of plants within an entire field. The time in which symptoms of plant injury occur is related to nematode population density, crop susceptibility, and prevailing environmental conditions. Under heavy nematode infestation, crop seedlings or transplants may fail to develop, maintaining a stunted condition, or die, causing poor or patchy stand development. Under less severe infestation levels, symptom expression may be delayed until later in the crop season after a number of nematode reproductive cycles have been completed on the crop. With time and reduction in root system size and function, symptoms become more pronounced and diagnostic. Root symptoms induced by sting or root-knot nematodes can oftentimes be as specific as above ground symptoms. Sting nematode can be very injurious, causing infected plants to form a tight mat of short roots, oftentimes assuming a swollen appearance. New root initials generally are killed by heavy infestations of the sting nematode, a symptom reminiscent of fertilizer salt burn. Root symptoms induced by root-knot cause swollen areas (galls) on the roots of infected tomato plants. Gall size may range from a few spherical swellings to extensive areas of elongated, convoluted, tumorous swellings which result from exposure to multiple and repeated infections. Symptoms of tomato root galling, can in most cases, provide positive diagnostic confirmation of nematode presence, infection severity, and potential for crop damage.Damage For most crop and nematode combinations, the damage caused by nematodes has not been accurately determined. Most vegetable crops produced in Florida are susceptible to nematode injury, particularly by root-knot and sting nematodes. Tomato plant symptoms and yield reductions are often directly related to preplant infestation levels in soil and to other environmental stresses imposed upon the plant during crop growth. As infestation levels increase, so does the amount of damage and yield loss. Given the possible levels of imprecision of extracting nematodes from soil, the mere presence of root-knot or sting nematodes suggests a potentially serious tomato production problem, particularly on warm sandy ground during the fall when soil temperatures favor high levels of nematode activity. At very high levels, typical of those which might occur under doubling cropping, plants may be killed. Tomato transplants, unlike direct seed, may tolerate higher initial population levels without incurring as significant a yield loss.Field Diagnosis and SamplingBecause of the microscopic size of nematodes and their irregular field distribution, soil and root tissue samples are usually required to determine whether nematodes are causing poor crop growth or to determine the need for nematode management. For nematodes, sampling and management is 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 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. Nematode species identification is currently only of practical value when rotation schemes or resistant varieties are available for nematode management. This information must then be coupled with some estimate of the expected damage to formulate an appropriate nematode control strategy. An advisory or predictive sample is a sample taken to predict the risk of nematode injury to a newly planted crop and 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 10 to 20 field locations using a cylindrical sampling tube or, if unavailable, a trowel or shovel. Since most species of nematodes are concentrated in the crop rooting zone, samples should be collected to a soil
Tomato Production Guide for Florida: Nematode Control Page 3 February 1998depth of 6 to 10 inches. Sample in a regular pattern over the area, emphasizing removal of samples across rows rather than along rows. One sample should represent no more than 10 acres for relatively lowvalue crops and no more than five acres for high value crops. Fields which have different crops (or varieties) during the past season or have obvious differences either in soil type or a 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. For diagnostic purposes on established plants, roots and soil cores should be removed to a depth of 6 to 10 inches from 10 to 20 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 insure sufficient quantities of infested roots and soil. Submission of additional samples, from adjacent areas of good growth, should also be considered for comparative purposes. For either type of sample, once all soil cores or samples are collected, the entire sample should be mixed thoroughly but carefully, and a one to two 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 40 to 60 ( F is recommended. Recognizing that the root-knot nematode causes the formation of large swollen areas or galls on the root systems of susceptible crops, relative population levels and field distribution of this nematode can be largely determined by simple examination of the crop root system for root gall severity. Root gall severity is a simple measure of the proportion of the root system which is galled. Immediately after final harvest, a sufficient number of plants should be carefully removed from soil and examined to characterize the nature and extent of the problem within the field. In general, soil population levels increase with root gall severity. This form of sampling can, in many cases, provide immediate confirmation of a nematode problem and allows mapping of current field infestation. As inferred previously, the detection of any level of root galling usually suggests a nematode problem for planting a susceptible crop, particularly within the immediate areas from which the galled plant(s) were recovered.General Management ConsiderationsNematode management should only be considered after the results of soil and root sampling are available. The agency or company that processed the samples should be able to indicate whether potential nematode problems exist within a field. However, it is important to remember that, in most cases, nematode management should not be considered until all other potential causes of crop decline or loss are evaluated and corrected. For more detailed information on treatment decisions and methods of nematode management in tomato, consult the Florida Nematode Control Guide, SP-54 and/or your County Extension Office. Currently nematode management considerations include crop rotation of less susceptible crops, resistant varieties, cultural and tillage practices, use of transplants, and preplant nematicide treatments. Where practical, these practices are generally integrated into the summer or winter 'off-season' cropping sequence. It should be recognized that not all land management and cultural control practices are equally effective in controlling plant parasitic nematodes and varying degrees of nematode control should be expected. These methods, unlike other chemical methods, tend to reduce nematode populations gradually through time.Crop RotationFor crop rotation to be effective, crops unsuitable for nematode infection, growth, or reproduction must be introduced into the rotation sequence. In most of Florida, it is not uncommon to observe a multispecies community of nematodes all occurring within the same field. Under these circumstances, it may not be possible to find a rotation or cover crop which will
Tomato Production Guide for Florida: Nematode Control Page 4 February 1998effectively reduce populations of all nematode pests, particularly if root-knot and sting nematodes occur in combination. In this case, crop rotations detrimental to root-knot, which is generally the most difficult to control, should be selected. Several forages and pasture grasses have been identified as potential rotation crops, particularly for producers with cattle operations. Current interest in forage legumes, like velvetbean, is related to their nitrogen-fixing potential, as well as their poor or nonhost status to root-knot and sting nematode. Use of nematoderesistant rotation crops can, however, be limited by stand establishment problems and weed proliferation. Weed recolonization, particularly of broadleaf species, is important because it may not be possible to manage root-knot nematodes with crop rotation if weeds are not simultaneously controlled. In other cases, resistant crop varieties are available which can be used within the rotation sequence to minimize problems to some species of root-knot but not sting nematodes. In California, rootknot nematode resistant cowpea, processing tomato, and nonhost winter grains are used in rotation to manage the southern root-knot nematode, M. incognita In some cases, therefore, species identification from soil and root tissue samples will be necessary to select the appropriate resistant varieties in a crop rotation as a nematode management option. FallowingClean fallow during the off-season can be a very important and effective cultural control measure available for nematodes. When food sources are no longer readily available, soil population densities of nematodes gradually decline with death occurring as a result of starvation. Due to the wide host range of many nematode species, weeds and crop volunteers must be controlled during the fallow period to prevent nematode reproduction and further population increase. At least two disking operations are generally required to maintain clean fallow soil conditions during the interim period between crops. Fallowing by use of herbicides to deplete nematode populations is a much slower process because the soil is not disturbed, thereby subjecting nematodes from deeper soil layers to the drying action of sun and wind. The unfavorable effects of fallowing on soil organic matter and soil structure is usually more than compensated for by the level of nematode control achieved and the resulting increase in crop productivity. When soil erosion is a potentially serious problem other measures should be considered.Resistant VarietiesFresh market tomato varieties with resistance to the root-knot nematode and adapted for Florida environment conditions have only recently become commercially available as a tactic for nematode management. In these resistant varieties, nematodes fail to develop and reproduce normally within tomato root tissues, allowing plants to grow and produce fruit even though nematode infection of roots occurs. At present, all resistant tomato varieties are effective against the major root-knot nematode species found in Florida. Presently, tomato plant resistance to root-knot nematode is conferred by a single dominant gene designated Mi. Under conditions of high soil temperature (i.e., 80 90 ( F), resistance of the Mi gene can be diminished or broken, rendering the resistant plant susceptible to nematode infection and damage. Due to the known heat instability of the Mi gene, successful use of these new resistant tomato varieties may preclude them to spring plantings, when cooler soil temperatures prevail. Also, given the potential development of resistance-breaking races of the root-knot nematode after repeated planting of resistant crop varieties, it may also be necessary to alternate the use of resistant and susceptible tomato varieties to avoid population shifts of nematodes towards resistance-breaking races. Other Cultural and Biological Methods At present there are no effective, commercially available, biological control agents which can be successfully used to control nematodes. Flooding has be shown to suppress nematode populations. Alternating two to three week cycles of flooding and drying have proven to be more effective than long, continuous flooding cycles. At present, only limited areas within the state are situated to take advantage of flooding as a viable means of nematode control.
Tomato Production Guide for Florida: Nematode Control Page 5 February 1998Other cultural measures which can be important in reducing nematode problems include rapid destruction of the infested crop root system following harvest. Fields which are disked as soon as possible after the crop is harvested will not only prevent further nematode population growth but subject existing populations to desiccation by sun and wind. Use of nematode free transplants is also recommended since direct seeded plants are particularly susceptible since they are vulnerable to injury for a longer duration, during an early, but critical period of crop development. In most cases, a combination of these management practices will substantially reduce nematode population levels, but will rarely bring them below economically damaging levels. This is especially true of lands which are continuously planted to susceptible crop varieties. In these cases, some form of pesticide assistance may still be necessary to improve tomato crop production.Chemical Control Fumigant Nematicides. In Florida, use of broad spectrum fumigants like methyl bromide have been shown to effectively reduce nematode populations and increase tomato crop yields, particularly when compared with nonfumigant nematicides. Since these products must diffuse through soil as gases to be effective, the most efficient fumigations occur when the soil is well drained, in seedbed condition, and at temperatures above 60 ( F. All of the fumigants are phytotoxic to plants and as a precautionary measure should be applied at least three weeks before crops are planted. When applications are made in the spring during periods of low soil temperature, these products can remain in the soil for an extended period, thus delaying planting or possibly causing phytotoxicity to a newly planted crop. Field observations also suggest rainfall or irrigation, which saturates the soil after treatment, tends to retain phytotoxic residues for longer periods, particularly in deeper soil layers.Nonfumigant Nematicides. All of the nonfumigant nematicides, currently registered for use, are soil applied. They must be incorporated with soil or carried by water into soil to be effective. These compounds must be uniformly applied to soil, targeting the application toward the future rooting zone of the plant, where they will contact nematodes, or in the case of systemics, in areas where they can be readily absorbed. Placement within the top two to four inches of soil should provide a zone of protection for seed germination, transplant establishment, and protect initial growth of plant roots from seeds or transplants. Most studies which have been performed in Florida and elsewhere to evaluate non-fumigant nematicides have not always been consistent, either for controlling intended pests or for obtaining consistent economic returns to the grower, particularly when compared with the broad spectrum fumigants. As the name implies, they are specific to nematodes, requiring integrated use of other chemical or pest control measures. Many are reasonably mobile and are readily leached in our sandy, low organic soils, thus requiring special consideration to irrigation practices and management.SummaryIn summary, nematode control measures can be conveniently divided into two major categories, including cultural and chemical control measures. With the anticipated loss of methyl bromide for soil fumigation purposes (January 1, 2001), it is apparent that none of these measures should continue to 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 which further enforces 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.