Cotton Root Protection from Plant-Parasitic Nematodes by Abamectin-Treated Seed

Abamectin is nematicidal to Meloidogyne incognita and Rotylenchulus reniformis, but the duration and length of cotton taproot protection from nematode infection by abamectin-treated seed is unknown. Based on the position of initial root-gall formation along the developing taproot from 21 to 35 d after planting, infection by M. incognita was reduced by abamectin seed treatment. Penetration of developing taproots by both nematode species was suppressed at taproot length of 5 cm by abamectin-treated seed, but root penetration increased rapidly with taproot development. Based on an assay of nematode mobility to measure abamectin toxicity, the mortality of M. incognita associated with a 2-d-old emerging cotton radicle was lower than mortality associated with the seed coat, indicating that more abamectin was on the seed coat than on the radicle. Thus, the limited protection of early stage root development suggested that only a small portion of abamectin applied to the seed was transferred to the developing root system.     

Role of Nematodes,Nematicides, and Crop Rotation on the Productivity and Quality of Potato,Sweet Potato,Peanut, and Grain Sorghum

The objective of this experiment was to determine the effects of fenamiphos 15G and short-cycle potato (PO)-sweet potato (SP) grown continuously and in rotation with peanut (PE)-grain sorghum (GS) on yield, crop quality, and mixed nematode population densities of Meloidogyne arenaria, M. hapla, M. incognita, and Mesocriconema ornatum. Greater root-gall indices and damage by M. hapla and M. incognita occurred on potato than other crops. Most crop yields were higher and root-gall indices lower from fenamiphos-treated plots than untreated plots. The total yield of potato in the PO-SP and PO-SP-PE-GS sequences increased from 1983 to 1985 in plots infested with M. hapla or M. arenaria and M. incognita in combination and decreased in 1986 to 1987 when root-knot nematode populations shifted to M. incognita. The total yields of sweet potato in the PO-SP-PE-GS sequence were similar in 1983 and 1985, and declined each year in the PO-SP sequence as a consequence of M. incognita population density increase in the soil. Yield of peanut from soil infested with M. hapla increased 82% in fenamiphos-treated plots compared to untreated plots. Fenamiphos treatment increased yield of grain sorghum from 5% to 45% over untreated controls. The declining yields of potato and sweet potato observed with both the PO-SP and PO-SP-PE-GS sequences indicate that these crop systems should not be used longer than 3 years in soil infested with M. incognita, M. arenaria, or M. hapla. Under these conditions, these two cropping systems promote a population shift in favor of M. incognita, which is more damaging to potato and sweet potato than M. arenaria and M. hapla.     

Alternatives to Fenamiphos for Management of Plant-Parasitic Nematodes on Bermudagrass

Plant-parasitic nematodes can be very damaging to turfgrasses. The projected cancellation of the registration for fenamiphos in the near future has generated a great deal of interest in identifying acceptable alternative nematode management tactics for use on turfgrasses. Two field experiments were conducted to evaluate the effectiveness of repeated applications of several commercially available nematicides and root biostimulants for reducing population densities of plant-parasitic nematodes and (or) promoting health of bermudagrass in nematode-infested soil. One experimental site was infested with Hoplolaimus galeatus and Trichodorus obtusus, the second with Belonolaimus longicaudatus. In both trials, none of the experimental treatments reduced population densities (P ≤ 0.1) of plant-parasitic nematodes, or consistently promoted turf visual performance or turf root production. Nematologists with responsibility to advise turf managers regarding nematode management should thoroughly investigate the validity of product claims before advising clientele in their use.     

Effect of a Terminated Cover Crop and Aldicarb on Cotton Yield and Meloidogyne incognita Population Density

Terminated small grain cover crops are valuable in light textured soils to reduce wind and rain erosion and for protection of young cotton seedlings. A three-year study was conducted to determine the impact of terminated small grain winter cover crops, which are hosts for Meloidogyne incognita, on cotton yield, root galling and nematode midseason population density. The small plot test consisted of the cover treatment as the main plots (winter fallow, oats, rye and wheat) and rate of aldicarb applied in-furrow at-plant (0, 0.59 and 0.84 kg a.i./ha) as subplots in a split-plot design with eight replications, arranged in a randomized complete block design. Roots of 10 cotton plants per plot were examined at approximately 35 days after planting. Root galling was affected by aldicarb rate (9.1, 3.8 and 3.4 galls/root system for 0, 0.59 and 0.84 kg aldicarb/ha), but not by cover crop. Soil samples were collected in mid-July and assayed for nematodes. The winter fallow plots had a lower density of M. incognita second-stage juveniles (J2) (transformed to Log₁₀ (J2 + 1)/500 cm³ soil) than any of the cover crops (0.88, 1.58, 1.67 and 1.75 Log₁₀(J2 + 1)/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). There were also fewer M. incognita eggs at midseason in the winter fallow (3,512, 7,953, 8,262 and 11,392 eggs/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). Yield (kg lint per ha) was increased by application of aldicarb (1,544, 1,710 and 1,697 for 0, 0.59 and 0.84 kg aldicarb/ha), but not by any cover crop treatments. These results were consistent over three years. The soil temperature at 15 cm depth, from when soils reached 18°C to termination of the grass cover crop, averaged 9,588, 7,274 and 1,639 centigrade hours (with a minimum threshold of 10°C), in 2005, 2006 and 2007, respectively. Under these conditions, potential reproduction of M. incognita on the cover crop did not result in a yield penalty.     

Population Dynamics of Meloidogyne incognita,M. arenaria,and Other Nematodes and Crop Yields in Rotations of Cotton,Peanut, and Wheat Under Minimum Tillage

Wheat, cotton, and peanut were arranged in three cropping sequences to determine the effects of fenamiphos (6.7 kg a.i./ha) and cropping sequence on nematode population densities and crop yields under conservation tillage and irrigation for 6 years. The cropping sequences included a wheat winter cover crop each year and summer crops of cotton every year, peanut every year, or cotton rotated every other year with peanut. The population densities of Meloidogyne spp. and Helicotylenchus dihystera were determined monthly during the experiment. Numbers of M. incognita increased on cotton and decreased on peanut, whereas M. arenaria increased on peanut, and decreased on cotton; both nematode species remained in moderate to high numbers in plots of wheat. Root damage was more severe on cotton than peanut and was not affected by fenamiphos treatment. The H. dihystera population densities were highest in plots with cotton every summer, intermediate in the cotton-peanut rotation, and lowest in plots with peanut every summer. Over all years and cropping sequences, yield increases in fenamiphos treatment over untreated control were 9% for wheat, 8% for cotton, and 0% for peanut. Peanut yields following cotton were generally higher than yields following peanut. These results show that nematode problems may be manageable in cotton and peanut production under conservation tillage and irrigation in the southeastern United States.     

Crop Yields and Nematode Population Densities in Triticale-Cotton and Triticale-Soybean Rotations

Triticale cv. Beagle 82, cotton cv. McNair 235, and soybean cv. Twiggs were arranged in three cropping sequences to determine the effects of fenamiphos and cropping sequence on nematode population densities and crop yields under conservation tillage for 4 years. The cropping sequences were triticale (T)-cotton (C)-T-C, T-soybean (S)-T-S, and T-C-T-S. Numbers of Meloidogyne incognita second-stage juveniles declined on trificale but increased on cotton and soybean each year. Root-gall indices of cotton and soybean ranged from 1.00 to 1.08 (1 to 5 scale: 1 = 0%, 2 = 1% to 25%, 3 = 26% to 50%, 4 = 51% to 75%, and 5 = 76% to 100% of roots galled) each year and were not affected by fenamiphos treatment or cropping sequence. Numbers of Pratylenchus brachyurus were maintained on trificale and generally increased more on soybean than on cotton. Population densities of Helicotylenchus dihystera were near or below detection levels in all plots during the first year and increased thereafter in untreated plots in the T-C-T-C and T-S-T-S sequences. Generally, yields of triticale in all cropping sequences declined over the years. Yields of cotton and soybean were not affected by fenamiphos at 6.7 kg a.i./ha. Cotton and soybean were grown successfully with little or no suppression in yields caused by nematodes in conservation tillage following triticale harvested for grain.     

Effects of Site-specific Application of Aldicarb on Cotton in a Meloidogyne incognita-infested Field

Cotton farmers in Missouri commonly apply a single rate of aldicarb throughout the field at planting to protect their crop from Meloidogyne incognita, even though these nematodes are spatially aggregated. Our purpose was to determine the effect of site-specific application of aldicarb on cotton production in a field infested with these nematodes in 1997 and 1998. Cotton yields were collected from sites not treated with aldicarb (control), sites receiving aldicarb at the standard recommended rate of 0.58 kg a.i./ha, and sites receiving specific aldicarb rates based on the soil population densities of second-stage infective juveniles of root-knot nematode. Yields for the standard rate and site-specific rate treatments were similar and greater (P ≤ 0.05) than the control treatment. Less aldicarb was used for the site-specific than the uniform-rate treatment each year—46% less in 1997 and 61% less in 1998. Costs associated with the site-specific treatment were very high compared with the uniform-rate treatment due to a greater number of soil samples analyzed for nematodes. Site-specific application of aldicarb for root-knot nematode management in cotton may pose fewer environmental risks than the uniform-rate application of aldicarb.     

Effects of One and Two Applications of Nematicides on Nematode Populations and Soybean Yields

Yields of ''McNair 800'' soybeans, Glycine max (L.) Merr., were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied at-planting and with phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Meloidogyne incognita (Kofoid and White) Chitwood. Yields of ''GaSoy 17'' were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied, preplant and with DBCP, carbofuran, phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Hoplolaimus columbus Sher. In several instances, preplant or at-planting treatments plus postplant treatments with the same or different chemicals were more effective than either treatment alone. Generally, the fumigants were more effective than the nonfumigants when they were applied at-planting to M. incognita-infested soil and preplant to H. columbus-infested soil. Phenamiphos, aldicarb, and DBCP were about equally effective when they were applied postplant in M. incognita-infested soil, but DBCP was more effective than carbofuran. Carbofuran, phenamiphos, aldicarb, and DBCP were about equally effective when applied postplant to H. columbus-infested soil.     

Crop Rotation and Herbicide Effects on Population Densities of Plant-Parasitic Nematodes

The influence of herbicides and mono- and multicropping sequences on population densities of nematode species common in corn, cotton, peanut, and soybean fields in the southeastern United States was studied for 4 years. Each experimental plot was sampled at monthly intervals. The application of herbicides did not significantly affect nematode population densities. Meloidogyne incognita and Trichodorus christiei increased rapidly on corn and cotton, but were suppressed by peanut and soybean. More Pratylenchus spp. occurred on corn and soybean than on cotton and peanut. Criconemoides ornatus increased rapidly on corn and peanut, but was suppressed by cotton and soybean. Helicotylenchus dihystera was more numerous on cotton and soybean than on corn and peanut. Numbers of Xiphinema americanum remained low on all crops. The peanut sequence was the most effective monocrop system for suppressing most nematode species. Multi-crop systems, corn-peanut-cotton-soybean and cotton-soybean-corn-peanut, were equally effective in suppressing nematode densities.     

Interaction of Meloidogyne incognita and Water Stress in Two Cotton Cultivars

A series of controlled-environment experiments were conducted to elucidate the effects of Meloidogyne incognita on host physiology and plant-water relations of two cotton (Gossypium hirsutum) cultivars that differed in their susceptibility to nematode infection. Inoculation of M. incognita-resistant cultivar Auburn 634 did not affect growth, stomatal resistance, or components of plant-water potential relative to uninoculated controls. However, nematode infection of the susceptible cultivar Stoneville 506 greatly suppressed water flow through intact roots. This inhibition exceeded 28% on a root-length basis and was similar to that observed as a consequence of severe water stress in a high evaporative demand environment. Nematodes did not affect the components of leaf water potential, stomatal resistance, transpiration, or leaf temperature. However, these factors were affected by the interaction of M. incognita and water stress. Our results indicate that M. incognita infection may alter host-plant water balance and may be a significant factor in early-season stress on cotton seedlings.     

Reproduction of Meloidogyne incognita on Winter Cover Crops Used in Cotton Production

Substantial reproduction of Meloidogyne incognita on winter cover crops may lead to damaging populations in a subsequent cotton (Gossypium hirsutum) crop. The amount of population increase during the winter depends on soil temperature and the host status of the cover crop. Our objectives were to quantify M. incognita race 3 reproduction on rye (Secale cereale) and several leguminous cover crops and to determine if these cover crops increase population densities of M. incognita and subsequent damage to cotton. The cover crops tested were ‘Bigbee’ berseem clover (Trifolium alexandrinum), ‘Paradana’ balansa clover (T. balansae), ‘AU Sunrise’ and ‘Dixie’ crimson clover (T. incarnatum), ‘Cherokee’ red clover (T. pratense), common and ‘AU Early Cover’ hairy vetch (Vicia villosa), ‘Cahaba White’ vetch (V. sativa), and ‘Wrens Abruzzi’ rye. In the greenhouse tests, egg production was greatest on berseem clover, Dixie crimson clover, AU Early Cover hairy vetch, and common hairy vetch; intermediate on Balansa clover and AU Sunrise crimson clover; and least on rye, Cahaba White vetch, and Cherokee red clover. In both 2002 and 2003 field tests, enough heat units were accumulated between 1 January and 20 May for the nematode to complete two generations. Both AU Early Cover and common hairy vetch led to greater root galling than fallow in the subsequent cotton crop; they also supported high reproduction of M. incognita in the greenhouse. Rye and Cahaba White vetch did not increase root galling on cotton and were relatively poor hosts for M. incognita. Only those legumes that increased populations of M. incognita reduced cotton yield. In the southern US, M. incognita can complete one to two generations on a susceptible winter cover crop, so cover crops that support high nematode reproduction may lead to damage and yield losses in the following cotton crop. Planting rye or Meloidogyne-resistant legumes as winter cover crops will lower the risk of increased nematode populations compared to most vetches and clovers.     

Penetration and Postinfection Development of Meloidogyne incognita on Cotton as Affected by Glomus intraradices and Phosphorus

The influence of the vesicular-arbuscular mycorrhizal fungus Glomus intraradices (Gi) and superphosphate (P) on penetration, development, and reproduction of Meloidogyne incognita (Mi) was studied on the Mi-susceptible cotton cultivar Stoneville 213 in an environmental chamber at 28 C. Plants were inoculated with Mi eggs at planting or after 28 days and destructively sampled 7, 14, 21, and 28 days after nematode inoculation. Mi penetration after 7 days was similar in all treatments at either inoculation interval. At 28 days, however, nematode numbers were least in mycorrhizal root systems and greatest in root systems grown with supplemental P. The rate of development of second-stage juveniles to ovipositing females was unaffected by Gi or P when Mi was added at planting, but was delayed in mycorrhizal root systems when Mi was added 28 days after planting. Nematode reproduction was lower in mycorrhizal than in nonmycorrhizal root systems at both Mi inoculation intervals. Nematode reproduction was stimulated by P when Mi was added at planting, but was similar to reproduction in the low P nonmycorrhizal treatment when Mi was added 28 days after planting. Eggs per female were increased by P fertility when Mi was added at planting.     

Light Intensity and Quality Effects on Reproduction of Plant-Parasitic Nematodes

Growing cotton in a greenhouse with 12-h of supplemental light [8,608 lux (800 ft-c) from combination of mercury and Lucalux® lamps] resulted in 2 × to > 3 × greater reproduction of Meloidogyne incognita and Belonolaimus longicaudatus as compared to natural light alone. Rate of increase of Hoplolaimus galeatus was affected little in this experiment. In a second experiment under controlled conditions in a phytotron, light source and intensity had greater influence on the reproduction of Heterodera glycines and Pratylenchus penetrans on soybean than on B. longicaudatus. Fluorescent plus incandescent and metal halide light sources resulted in the greatest nematode reproduction. Lucalux lamps resulted in much lower rates of nematode increase than other light sources. Rates of nematode increase on soybean under the different light sources in the phytotron generally were positively related to plant growth.     

Granular Nematicides as Adjuncts to Fumigants for Control of Cotton Root-knot Nematodes

Growth and yield of cotton were best with combinations of fumigants and organophosphate and carbamate nematicides. Organophosphates or carbamates used alone did not give season-long control of root-knot nematodes. Long-term control was poor because the temporary sublethal effects of these materials diminished soon enough lhat the nematodes could reproduce. The nematodes survived the treatments and a year of nonhost culture, and damaged a susceptible host crop 2 years after treatment. No such damage occurred in plots treated with fumigant, fumigant plus organophosphate, or fumigant plus carbamate. Treatment of seed and treatment of cotton, either in furrow at planting or sidedressing at midseason, with organophosphate and carbamate nematicides resulted in little or no yield increase, because nematode control was only minimal and temporary; or in a yield decrease, because the toxicity of the materials was manifested when nematode populations were low.     

Damage Function and Economic Threshold for Belonolaimus longicaudatus on Potato

Belonolaimus longicaudatus has long been recognized as a pathogen of potato (Solanum tuberosum). However, a damage function relating expected yield of potato to population densities of B. longicaudatus at planting has not been derived, and the economic threshold for nematicide application is unknown. The objectives of this study were to derive the damage function of B. longicaudatus on potato and to calculate the economic threshold population density. The damage function data for B. longicaudatus on potato were obtained from an ongoing field study to evaluate cropping systems and nematode management practices. Soil samples were collected from experimental field plots, and nematodes were extracted from a 130-cm³ subsample with a centrifugal-flotation method. A damage function was derived by linear regression of potato yield on nematode population density at planting. Based on this derived damage function and published potato prices, the economic threshold for nematicide application was calculated at 2 to 3 B. longicaudatus/130 cm³ of soil, which was near the detection threshold based on methodology used in this study.     

Vertical Distribution of Plant-parasitic Nematodes in Sandy Soil under Soybean

Vertical distribution of five plant-parasitic nematodes was examined in two north Florida soybean fields in 1987 and 1988. Soil samples were collected from 0-15 cm, 15-30 cm, and 30-45 cm deep at each site. Soil at the three depths consisted of approximately 96% sand. More than 50% of Belonolaimus longicaudatus population densities occurred in the upper 15-cm soil layer at planting, but the species became more evenly distributed through the other depths as the season progressed. Criconemella sphaerocephala was evenly distributed among the three depths in one field but was low (< 20% of the total density) in the upper 15 cm at a second site. Maximum population densities of Pratylenchus brachyurus were observed at 15-30 cm on most sampling dates. Vertical distributions of Meloidogyne incognita and Paratrichodorus minor were erratic and showed seasonal variation. A diagnostic sample from the upper 0-15 cm of these soybean fields revealed only a minority of the populations of most of the phytoparasitic species present.     

Entomopathogenic Nematodes Are Not an Alternative to Fenamiphos for Management of Plant-Parasitic Nematodes on Golf Courses in Florida

With the cancellation of fenamiphos in the near future, alternative nematode management tactics for plant-parasitic nematodes (PPN) on golf courses need to be identified. The use of entomopathogenic nematodes (EPN) has been suggested as one possible alternative. This paper presents the results of 10 experiments evaluating the efficacy of EPN at managing PPN on turfgrasses and improving turf performance. These experiments were conducted at various locations throughout Florida over the course of a decade. In different experiments, different EPN species were tested against different species of PPN. Separate experiments evaluated multiple rates and applications of EPN, compared different EPN species, and compared single EPN species against multiple species of PPN. In a few trials, EPN were associated with reductions in certain plant-parasite species, but in other trials were associated with increases. In most trials, EPN had no effect on plant parasites. Because EPN were so inconsistent in their results, we conclude that EPN are not acceptable alternatives to fenamiphos by most turf managers in Florida at this time.     

Evaluation of an Antibiotic-Producing Strain of Pseudomonas fluorescens for Suppression of Plant-Parasitic Nematodes

The antibiotic 2,4-diacetylphloroglucinol (DAPG), produced by some strains of Pseudomonas spp., is involved in suppression of several fungal root pathogens as well as plant-parasitic nematodes. The primary objective of this study was to determine whether Wood1R, a D-genotype strain of DAPG-producing P. fluorescens, suppresses numbers of both sedentary and migratory plant-parasitic nematodes. An experiment was conducted in steam-heated soil and included two seed treatments (with Wood1R and a control without the bacterium) and six plant-nematode combinations which were Meloidogyne incognita on cotton, corn, and soybean; M. arenaria on peanut; Heterodera glycines on soybean; and Paratrichodorus minor on corn. Wood 1R had no effect on final numbers of M. arenaria, P. minor, or H. glycines; however, final numbers of M. incognita were lower when seeds were treated with Wood1R than left untreated, and this reduction was consistent among host plants. Population densities of Wood1R were greater on the roots of corn than on the other crops, and the bacterium was most effective in suppressing M. incognita on corn, with an average reduction of 41%. Despite high population densities of Wood1R on corn, the bacterium was not able to suppress numbers of P. minor. When comparing the suppression of M. incognita on corn in natural and steam-heated soil, egg production by the nematode was suppressed in natural compared to steamed soil, but the presence of Wood1R did not result in additional suppression of the nematodes in the natural soil. These data indicate that P. fluorescens strain Wood1R has the capacity to inhibit some populations of plant-parasitic nematodes. However, consistent suppression of nematodes in natural soils seems unlikely.     

Control of Root-knot Nematodes on Tomato in Stone Wool Substrate with Biological Nematicides

The efficacy of four biological nematicides on root-galling, root-knot nematode (Meloidogyne incognita) reproduction, and shoot weight of tomato (Solanum lycopersicum) grown in stone wool substrate or in pots with sandy soil was compared to an oxamyl treatment and a non-treated control. In stone wool grown tomato, Avid® (a.i. abamectin) was highly effective when applied as a drench at time of nematode inoculation. It strongly reduced root-galling and nematode reproduction, and prevented a reduction in tomato shoot weight. However, applying the product one week before, or two weeks after nematode inoculation was largely ineffective. This shows that Avid® has short-lived, non-systemic activity. The effects of Avid® on nematode symptoms and reproduction on soil-grown tomato were only very minor, probably due to the known strong adsorption of the active ingredient abamectin to soil particles. The neem derived product Ornazin® strongly reduced tomato root-galling and nematode reproduction only in stone wool and only when applied as a drench one week prior to nematode inoculation, suggesting a local systemic activity or modification of the root system, rendering them less suitable host for the nematodes. This application however also had some phytotoxic effect, reducing tomato shoot weights. The other two products, Nema-Q™ and DiTera®, did not result in strong or consistent effects on nematode symptoms or reproduction.     

Relationships Between Tolerance and Resistance to Meloidogyne incognita in Cotton

The southern root-knot nematode, Meloidogyne incognita, is the most damaging pathogen of cotton in the United States, and both resistance and tolerance to M. incognita could be valuable management approaches. Our objectives were to evaluate advanced cotton breeding lines for resistance and tolerance to M. incognita and to determine if a relationship between resistance and tolerance exists. Reproduction of M. incognita was evaluated on 17 breeding lines, a susceptible control (Delta and Pine Land DP5415), and a resistant control (M-120) in two greenhouse trials with six replications in a randomized complete block design. Two-week-old seedlings were inoculated with 8,000 M. incognita eggs and assessed for egg production 8 weeks later. Reproduction on the resistant control was only 10% of that on the susceptible control. Eight breeding lines supported 45% to 57% less (P <= 0.05) nematode reproduction than the susceptible control, and none of them were as resistant as M-120. Yield was determined in 2001 and 2002 in fumigated (1,3-dichloropropene at 56 liters/ha) and nonfumigated plots in a strip-plot design with three replications in a field naturally infested with M. incognita. Yield suppression caused by nematode infection differed among genotypes (P ≤ 0.05 for genotype × fumigation interaction). Six genotypes in 2001 and nine in 2002 were tolerant to M. incognita based on no difference in yield between the fumigated and nonfumigated plots (P ≥ 0.10). However, only three genotypes had no significant yield suppression in both years, of which two also were resistant to M. incognita. Regression analysis indicated that yield suppression decreased linearly as nematode resistance increased.