The effects of cropping systems (fallow, rotation with sorghum-sudangrass hybrid [Sorghum bicolor × S. sudanense], and continuous soybean [Glycine max]), nematicide (aldicarb) treatment, and soybean cultivar on yield and nematode population densities were studied in a field infested with a mixture of Meloidogyne spp. and Heterodera glycines. Soybean following sorghum-sudangrass yielded 111 kg/ha more than soybean following fallow and 600 kg/ha more than continuous soybean. Aldicarb treatment increased yield by 428 kg/ha, regardless of previous crop. Cultivars interacted significantly with nematicide treatment and previous crop with respect to yield. Sorghum-sudangrass reduced numbers of Meloidogyne spp. compared with fallow and continuous soybean, but cropping system did not affect H. glycines numbers. The cultivar × previous crop and cultivar × nematicide interactions were significant for numbers of Meloidogyne spp. and H. glycines. We concluded that sorghum-sudangrass hybrid and fallow are effective in reducing yield losses caused by mixed populations of Meloidogyne and H. glycines. Highest yields were obtained using crop rotation and cultivars with the highest levels of resistance to both nematodes.
aldicarb; biodiversity; crop rotation; Glycine max; Heterodera glycines; host-plant resistance; Meloidogyne; nematode; root-knot nematode; sorghum-sudangrass; Sorghum bicolor; Sorghum sudanense; soybean cyst nematode; soybean
The response of softwood cuttings of Myrobalan plum infested after 50 and 105 days with 3,000 second-stage juveniles (J2) of Meloidogyne arenaria was compared to 15-month-old hardwood cuttings in 13 genotypes ranging from highly resistant to susceptible. Gall index and number of galls were recorded 30 days after infestation. Fifty-day-old cuttings rooted in perlite developed many rootlets, but had only incipient galls after infestation. In sand, rooting of 50-day-old cuttings not treated with indolebutyric acid (IBA) hormone was so variable that their resistance could not be assessed. Similar cuttings rooted with IBA developed more galls, but neither number of galls per plant nor gall index was a reliable criterion for determination of host suitability. Because of the better rooting results with IBA treatment, 105-day-old cuttings were first rooted with IBA in perlite and then transferred into sand for nematode inoculation. Known highly resistant genotypes of Myrobalan plum were gall-free and the responses of other genotypes paralleled that of the reference hardwood cuttings, although the test was less discriminating. Expression of M. arenaria host suitability in Myrobalan plum depends on root tissue maturation and cannot be reliably evaluated with 50-day-old cuttings.
hardwood cutting; host suitability; Meloidogyne arenaria; nematode; Prunus cerasifera; resistance; root galling; root-knot nematode; softwood cutting
We tested the hypothesis that isolates of Hirsutella rhossiliensis from host nematodes in the family Hoplolaimidae (Rotylenchus robustus and Hoplolaimus galeatus) would be more virulent to R. robustus than would isolates from host nematodes not in the Hoplolaimidae (Heterodera schachtii and Criconemella xenoplax). Nematodes were touched to 10-20 spores of different isolates and incubated at 20 C in 4.5 mM KC1; the percentage of nematodes colonized (filled with hyphae) was determined after 2, 5, 10, 20, and 30 days. The hypothesis was rejected because isolates from H. schachtii and C. xenoplax were equivalent or better at parasitizing R. robustus than were isolates from R. robustus and H. galeatus. In addition, the R. robustus and H. galeatus isolates were as pathogenic to C. curvata as they were to R. robustus, but produced fewer spores per colonized nematode (H. schachtii) than did the other isolates.
biological control; endoparasite; fungus; Hirsutella rhossiliensis; host specificity; parasitism; Rotylenchus rotmstus; virulence
Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is a major pest of soybean, Glycine max L. Merr. Soybean cultivars resistant to SCN are commonly grown in nematode-infested fields. The objective of this study was to examine the stability of SCN resistance in soybean genotypes at different soil temperatures and pH levels. Reactions of five SCN-resistant genotypes, Peking, Plant Introduction (PI) 88788, Custer, Bedford, and Forrest, to SCN races 3, 5, and 14 were studied at 20, 26, and 32 C, and at soil pH's 5.5, 6.5, and 7.5. Soybean cultivar Essex was included as a susceptible check. Temperature, SCN race, soybean genotype, and their interactions significantly affected SCN reproduction. The effect of temperature on reproduction was quadratic with the three races producing significantly greater numbers of cysts at 26 C; however, reproduction on resistant genotypes remained at a low level. Higher numbers of females matured at the soil pH levels of 6.5 and 7.5 than at pH 5.5. Across the ranges of temperature and soil pH studied, resistance to SCN in the soybean genotypes remained stable.
abiotic factors; Glycine max; Heterodera glycines; resistance; pH; soybean cyst nematode; temperature
In a field study conducted in Georgia, cucurbit plants with high (Cucurbita andreana) and low (Cucurbita maxima) concentrations of cucurbitacins were used in combination with two types of fertilizers to investigate their effects on the community of soil nematodes. Ecological measures of soil nematode community structure such as total nematode abundance, number of genera, trophic diversity, trophic group proportions, fungivore/bacterivore ratio, and modified maturity index were assessed and compared among treatments. In general, poultry manure (an organic source of nitrogen) and synthetic fertilizer (a nonorganic source of nitrogen) did not differ in their effects on the nematode communities throughout one growing season. Few differences between the two plant species were found for any of the nematode community measurements. Bacterial- and fungal-feeding nematodes were the most abundant trophic groups, averaging 60% and 20% of the nematode community, respectively. Trophic diversity, nematode maturity index, and fungivore/ bacterivore values were lowest at the beginning and highest at the end of the experiment.
Cucurbita andreana; cucurbitacins; Cucurbita maxima; ecology; fertilizer; nematode; secondary plant metabolite
The advantages of nucleotide sequence data for studying phylogeny have been shown to include number of potential characters available for comparison, rate independence between molecular and morphological evolution, and utility of molecular data for modeling patterns of nucleotide substitution. Potential pitfalls have also been revealed and include difficulties of inferring positional homology, incongruence between organismal and gene genealogies, and low likelihood of recovering the correct phylogeny given certain patterns in the timing of speciation events. Statistical methods for comparing phylogenetic hypotheses have been used to assess the reliability of alternative trees for ascaridoid nematodes. Based on partial ribosomal RNA sequences, tree topologies inconsistent with monophyly of the Ascaridinae were significantly worse by maximum likelihood inference. The topology of the maximum parsimony tree based on full-length sequences of 18S rRNA and 300 nucleotides of Cytochrome oxidase II for 13 ascaridoid species was generally consistent with traditional taxonomic expectations at lower ranks, but inconsistent with most proposed arrangements at higher taxonomic levels.
ascaridoid; cytochrome oxidase; molecular systematics; phylogenetics; ribosomal-RNA
The efficacy of mixtures of dry olive (Olea europea) pomace with biuret, guanidine, and melamine for control of root-knot nematodes (Meloidogyne spp.) on tomato (Lycopersicon esculentum) was studied in greenhouse experiments. Olive pomace (OP) applied pre-plant at 10 g/kg soil was phytotoxic. Mixtures of OP (10 g/kg soil) with biuret or guanidine at 200-300 mg/kg soil reduced or eliminated the phytotoxic effect, controlled root-knot nematodes, and increased soil esterase activity indicative of microbial activity. The addition of biuret or guanidine without OP to soil at rates <300 mg/kg soil did not control root-knot nematodes. Melamine applied at 100-400 mg/kg soil was phytotoxic as were mixtures of melamine with OP. Treatment of OP with anhydrous ammonia increased N content of the material. In another greenhouse experiment, NH₃-treated OP added to soil was not phytotoxic to tomato, suppressed root-knot nematodes, and increased soil esterase activity. Greenhouse and microplot experiments with OP plus chicken litter demonstrated the efficacy of these combination amendments to control root-knot nematodes and increase tomato yields in Meloidogyne-infested soil.
amendments; anhydrous ammonia; biuret; chicken litter; control; guanidine; melamine; Meloidogyne spp.; nematode; Olea europaea; olive pomace; tomato; root-knot nematode
Advance inoculation of the tomato cv. Celebrity or the pyrethrum clone 223 with host-incompatible Meloidogyne incognita or M. javanica elicited induced resistance to host-compatible M. hapla in pot and field experiments. Induced resistance increased with the length of the time between inoculations and with the population density of the induction inoculum. Optimum interval before challenge inoculation, or population density of inoculum for inducing resistance, was 10 days, or 5,000 infective nematodes per 500-cm³ pot. The induced resistance suppressed population increase of M. hapla by 84% on potted tomato, 72% on potted pyrethrum, and 55% on field-grown pyrethrum seedlings, relative to unprotected treatments. Pyrethrum seedlings inoculated with M. javanica 10 days before infection with M. hapla were not stunted, whereas those that did not receive the advance inoculum were stunted 33% in pots and 36% in field plots. The results indicated that advance infection of plants with incompatible or mildly virulent nematode species induced resistance to normally compatible nematodes and that the induced resistance response may have potential as a biological control method for plant nematodes.
Chrysanthemum cinerariifolium; induced resistance; Lycopersicon esculentum; Meloidogyne hapla; Meloidogyne incognita; Meloidogyne javanica; Mi gene; nematode; pyrethrum; root-knot nematode; tomato
Two cultivars of sudangrass (Piper and Trudan 8) and three of sorghum-sudangrass (Sordan 79, P855F, and P877F) were grown as green manure crops in 1993 and 1994 and compared with sweet corn for their impact on nematode population dynamics. Nematodes were identified to trophic group, order, and to lower taxa when possible. Population densities were determined after 7 weeks of crop growth and 3 weeks after incorporation of green crop residue. Plant-parasitic nematode genera included Pratylenchus, Longidorus, Xiphinema, and Paratrichodorus. The plant-feeder trophic group increased or was maintained on all crops after 7 weeks, at which time population densities were lowest on corn in 1993 and equivalent among crops in 1994. The total number of nematodes in the plant-feeder trophic group did not differ before and after incorporation in 1993 and increased for Piper sudangrass, Sordan 79 and P855F sorghum-sudangrass, and sweet corn in 1994. After incorporation, numbers of bacterial-feeding nematodes increased for all crops in 1994 and for Piper sudangrass in 1993. There were no consistent crop treatment effects on the fungal-feeding, omnivore, and predator trophic groups after incorporation.
control; green manure; nematode; organic amendment; potato; Sorghum bicolor; sudangrass; sorghum-sudangrass hybrid
Ten cultivated plants of the family Cruciferae were evaluated for susceptibility to Meloidogyne arenaria race 1, M. incognita races 1 and 3, and M. javanica in a series of four separate greenhouse tests. After 62-64 days, or 1,032-1,072 degree days (10 C base), several of the crops evaluated showed moderate to severe levels of galling (> 3.0 on 0-5 scale) and moderate numbers of egg masses (>2.0 on 0-5 scale) in response to each of the nematode species and races. Among the plants tested, collard (Brassica oleracea var. acephala) cv. Georgia Southern was the least susceptible (fewest galls and egg masses) to each of the four nematode isolates. Similar low levels of infection were obtained with broccoli (B. oleracea var. botrytis) cv. De Cicco in response to M. incognita race 1 and M. arenaria. Numbers of second-stage juveniles hatched from eggs per root system were variable in the test with M. arenaria, but lowest on collard for each of the other nematodes. Some commonly grown crucifers are hosts to several different species and races of Meloidogyne, which should be considered if these crops are included in cropping systems.
Brassica chinensis; Brassica napus; Brassica oleracea; Brassica rapa; broccoli; cabbage; canola; cauliflower; chinese cabbage; collard; host-plant resistance; Meloidogyne arenaria; Meloidogyne incognita; Meloidogyne javanica; mustard; nematode; radish; Raphanus sativus; Sinapis alba; turnip
While nematodes are sometimes regarded as osmoconformers, at least one species is capable of short-term osmoregulation over a wide range of osmotic environments, and the principal site of osmoregulation is the body wall. This general osmoregulation is important to the life of the nematode not only in confronting variations in the environment, but also in maintaining its hydrostatic skeleton. There is also evidence suggesting that compartments exist in some nematodes and that water exchange between the compartments is limited and slow. The ability to regulate the internal movements of water is important in molting and in the infective process. Hormones may be the mediators of osmotic control.
animal parasitic nematode; Haemonchus contortus; nematode; osmotic control; osmoregulation; Pseudoterranova decipiens; regulation; water compartment
Dry alginate-clay pellets containing mycelium of ARF18 were added to sandy soil in greenhouse tests to determine the formulation's efficacy in the suppression of Heterodera glycines. Pellet formulation variables included quantity of mycelium per pellet (0.0-3.9%), pellet size (2.3 or 8.3 mg), pellet application rate per unit soil (0.4 or 1.0% based on dry soil weight), and pellet storage (0 or 90 days). All of these variables affected efficacy. Nematode suppression was greatest (95%) with 8.3 mg pellets containing 3.9% mycelium that were not stored and applied at the rate of 1.0% of dry soil weight. Storage for 90 days reduced the efficacy of the pellets. The soybean cultivars tested were not equally good hosts of H. glycines, but reproduction of the nematode was reduced equally on all. The average suppression was 96% (range 86-99%). Similar suppression of reproduction occurred in tests with six races of H. glycines. ARF18 appeared to be nonspecific with regard to soybean cultivar and H. glycines race.
biological control; carriers; egg parasite; formulation; fungus; Glycine max; Heterodera glycines; kaolin; nematode; nematophagus; race; soybean cyst nematode
The effects of Meloidogyne incognita on the growth and water relations of cotton were evaluated in a 2-year field study. Microplots containing methyl bromide-fumigated fine sandy loam soil were infested with the nematode and planted to cotton (Gossypium hirsutum L.). Treatments included addition of nematodes alone, addition of nematodes plus the insecticide-nematicide aldicarb (1.7 kg/ha), and an untreated control. Meloidogyne incognita population densities reached high levels in both treatments where nematodes were included. Root galling, plant height at harvest, and seed cotton yield were decreased by nematode infection. In older plants (89 days after planting [DAP]), leaf transpiration rates and stomatal conductance were reduced, and leaf temperature was increased by nematode infection. Nematode infection did not affect (P = 0.05) leaf water potential in either young or older plants but lowered the osmotic potential. The maximum rate and cumulative amount of water flowing through intact plants during a 24-hour period were lower, on both a whole-plant and per-unit-leaf-area basis, in infected plants than in control plants. Application of aldicarb moderated some of the nematode effects but did not eliminate them.
aldicarb; cotton; Gossypium hirsutum; Meloidogyne incognita; nematicide; nematode; plant water relations; root-knot nematode; stomatal resistance; transpiration; water flux; water potential
In biological control studies of plant-parasitic nematodes in field soil improved methods are needed for reducing or eliminating specific soil inhabiting microorganisms. Microwave heating of soil decreases soilborne fungi and bacteria, but not Pasteuria spp. Bacterial and fungal colony forming units were reduced to nondetectable levels in microwaved heated field soft (650 watts) at 5.2% moisture when treated for 6 minutes and 4 minutes, respectively.
'Floratam' and 'FX-313' St. Augusfinegrasses (Stenotaphrum secundatum) were compared in a time-course experiment for host suitability and susceptibility to the lance nematode, Hoplolaimus galeatus. Nematode densities were determined in the soil and acid-fuchsin stained roots 42, 84, 126, 168, and 210 days after pots containing 230 cm³ of autoclaved native Margate fine sand/pot were infested with 104 ± 9 nematodes and maintained at 25 ± 2 C in the laboratory. 'FX-313' was a more suitable host for H. galeatus. Numbers of H. galeatus reached a maximum at 210 days after inoculation, with 5,550 and 4,120 nematodes (adults plus juveniles)/pot for 'FX-313' and 'Floratam,' respectively. Root and shoot dry weights of both grasses were not affected by H. galeatus throughout the experiment. Three polyploid, 2n = 30 to 32 ('Floratam,' 'FX-10,' and 'Bitterblue') and three diploid, 2n = 18 ('FX-313,' 'Florida Common,' and 'Seville') S. secundatum genotypes were inoculated with H. galeatus (99 ± 9/pot) and compared with uninoculated controls 210 days after inoculation. St. Augustinegrass genotypes differed as hosts of H. galeatus. 'FX-313' and 'Florida Common' represented the high and low extremes, respectively, for nematode reproduction (9,750 and 5,490 nematodes/pot or 4,239 and 2,387 nematodes/100 cm³ of soil). However, differences in root and shoot growth were not detected 210 days after inoculation with H. galeatus.
Hoplolaimus galeatus; lance nematode; nematode; population dynamics; resistance; St. Augustinegrass; Stenotaphrum secundatum; turfgrass breeding
Pearl millet is used mainly as a temporary forage crop in the southern United States. A new pearl millet hybrid has potential as a major grain crop in the United States. The effects of nematodes, irrigation, a nematicide, and nitrogen rates on a new pearl millet grain hybrid, HGM-100, and nematode population changes were determined in a 2-year study. Root-knot nematodes (Meloidogyne incognita race 1) entered the roots of pearl millet and caused minimal galling, but produced large numbers of eggs that hatched into second-stage juveniles. Root-gall indices ranged from 1.00 to 1.07 on a 1-5 scale and were not affected by irrigation or rates of nitrogen. Yield of pearl millet was up to 31% higher under no supplemental irrigation than under irrigation, 16% higher in fenamiphos-treated plots than untreated plots, and 56% higher in plots treated with 38 kg nitrogen/ha than plots treated with 85 kg nitrogen/ha. In southern Georgia, pearl millet appears to be resistant to ring nematode (Criconemella ornata) but favors development and reproduction of M. incognita.
chemical control; Criconemella ornata; irrigation; Meloidogyne incognita; millet; nematode; nitrogen; Pennisetum glaucum; ring nematode; root-knot nematode
Fusarium oxysporum f. sp. ciceri and Meloidogyne javanica are important pathogens of chickpea. Interrelationships between Fusarium oxysporum f. sp. ciceri and M. javanica were investigated on 53 Fusarium wilt-resistant chickpea genotypes in pot experiments. All of the genotypes were susceptible to M. javanica. Fusarium wilt resistance in one genotype (ICC 12275) was ineffective in the presence of M. javanica, and all the plants completely wilted. Resistance in four genotypes (ICCs 11319, 11322, 12254, 12272) was reduced in the presence of the nematode. Vascular discoloration above the collar region of the plants, an indication of susceptibility to the fungus, was observed. Wilt resistance in 48 genotypes was not modified by M. javanica. The effects of interactions between the pathogens on shoot and root weights, gall index, and galled area of root were significant only on 10-28% of the genotypes. Presence of the fungus reduced the adverse effects of nematodes on growth of 15% of the genotypes. Appraisal of wilt-resistant chickpea genotypes for their reactions to combinations of the two pathogens would help to identify and develop chickpea cultivars with wilt resistance stable in presence of M. javanica.
Cicer arietinum; interaction; Fusarium oxysporum f. sp. ciceri; Meloidogyne javanica; nematode; root-knot nematode; wilt resistance
Sixty-nine herbaceous perennial ornamentals in 56 genera were evaluated for root galling after 2 months in soil infested with Meloidogyne hapla under greenhouse conditions. Plants were rated susceptible or resistant based on the number of galls present on the root system. Thirty-six percent had more than 100 galls on the roots (similar to 'Rutgers' tomato controls) and were rated susceptible. Thirty percent of the plants tested did not have galls or egg masses present on the root system and were rated resistant. The remaining 34 percent were intermediate in response. Variation in response to M. hapla was observed within plant genera and species. The identification of M. hapla-resistant perennial ornamentals will aid in management of this nematode in landscapes and production fields.
Meloidogyne hapla; nematode; nonhost; ornamental; perennial; resistance; root-knot nematode
The efficacy of fallow and coastal bermudagrass (Cynodon dactylon) as a rotation crop for control of root-knot nematode (Meloidogyne incognita race 1) and soilborne fungi in okra (Hibiscus esculentus cv. Emerald), squash (Cucurbita pepo cv. Dixie Hybrid), and sweet corn (Zea mays cv. Merit) was evaluated in a 3-year field trial. Numbers of M. incognita in the soil and root-gall indices were greater on okra and squash than sweet corn and declined over the years on vegetable crops following fallow and coastal bermudagrass sod. Fusarium oxysporum and Pythium spp. were isolated most frequently from soil and dying okra plants. Numbers of colony-forming units of soilborne fungi generally declined as the number of years in sod increased, but were not affected by coastal bermudagrass sod. Yields of okra following 2-year and 3-year sod and squash following 2-year sod were greater than those following fallow. Yield of sweet corn was not different following fallow and coastal bermudagrass sod.
coastal bermudagrass; Cucurbita pepo; Cynodon dactylon; fallow; Hibiscus esculentus; management; Meloidogyne incognita; nematode; okra; root-knot; rotation; squash; sweet corn; Zea mays
Five cropping regimes involving combinations of 2 legumes, alfalfa (Medicago sativa) and yellow sweet dover (Melilotus officinalis), 2 monocots, corn (Zea mays) and sudax (Sorghum halupeuse × Sorghum sudanese), and potato (Solanum tuberosum cv. Superior) were tested for their impact on potato yields in a field infested with Pratylenchus penetrans and Verticillium dahliae. No differences in 1990 tuber yields were observed among the five cropping regimes (P < 0.05). In 1991, yields following 1 year of corn, sudax, sweet clover, or alfalfa and 2 years of potato were not different from that of 3 years of continuous potato (P < 0.05). Two years of sweet clover or alfalfa followed by potato resulted in significantly increased potato tuber yields compared with 3 years of potato (P < 0.05). The 2-year legume and 2-year grain rotations resulted in lower P. penetrans population densities at the end of the 3-year rotation compared with 3 years of continuous potato (P < 0.01). The highest preplant V. dahliae population density (34 cfu/g soil), together with a P. penetrans density of 12/100 cm³ of soil was in the sudax-sudax-potato cropping regime and resulted in the lowest potato tuber yield. The highest preplant P. penetrans population density (54/100 cm³ soil), together with a V. dahliae population density of 19.5 cfu/g soil was observed in the corn-corn-potato cropping regime and resulted in the second lowest potato tuber yield in 1991. After 3 years, potato tuber yields were negatively related to preplant densities of V. dahliae (r² = 0.237), P. penetrans (r² = 0.175), and both pathogens (r² = 0.380). A comprehensive regression model was developed to isolate pathogen effects on potato yields from cropping regime effects encompassing all 10 cropping regimes (r² = 0.915).
cropping regime; interaction; nematode; potato tuber yield; Pratylenchus penetrans; lesion nematode; Solanum tuberosum; Verticillium dahliae; verticillium wilt
In a field experiment conducted on sandy soil in Florida during the 1993 season, rotation crops of castor (Ricinus communis), velvetbean (Mucuna deeringina), 'Mississippi Silver' cowpea (Vigna unguiculata), American jointvetch (Aeschynomene americana), 'Dehapine 51' cotton (Gossypium hirsutum), and 'SX-17' sorghum-sudangrass (Sorghum bicolor × S. sudanense) were effective in maintaining low population densities (<12/100 cm³ soil) of Meloidogyne incognita race 1, whereas high population densities (>450/100 cm³ soil) resulted after 'Clemson Spineless' okra (Hibiscus esculentus) and 'Kirby' soybean (Glycine max). Following a winter cover crop of rye (Secale cereale), densities of M. incognita following the six most effective rotation crops (1993 season) remained relatively low (≤32/100 cm³ soil) through midseason of an eggplant (Solanum melongena) crop planted in 1994, but increased by the end of the eggplant crop. The rotation crops planted during 1993 had little effect on yield of eggplant in 1994. Eggplant yield was inversely correlated with preplant densities (Pi) of Belonolaimus longicaudatus (r = -0.282; P ≤ 0.10; 46 dr), but not with Pi of M. incognita. A separate microplot experiment conducted in 1994 revealed that final densities (Pf) of M. incognita race 1 following 13 different crop cultivars were lower (P ≤ 0.05) than Pf following a 'Pioneer X304C' corn (Zea mays) control, but only 'Mississippi Silver' cowpea and 'Sesaco 16' sesame (Sesamum indicum) resulted in lower (P ≤ 0.05) Pf of Paratrichodorus minor than the corn control. It is critical that rotation crops intended for suppression of individual Meloidogyne spp. be evaluated for their response to other nematode pests as well.
Aeschynomene americana; Belonolaimus longicaudatus; Criconemella spp.; crop rotation; cropping system; eggplant; Glycine max; Gossypium hirsutum; Helicotylenchus dihystera; Hibiscus escutentus; Meloidogyne incognita; Mucuna deeringiana; nematode; nematode management; Paratrichodorus minor; Pratylenchus spp.; Ricinus communis; Sesamum indicum; Solanum melongena; Sorghum bicolor; sustainable agriculture; Tagetes patula; Vigna unguiculata; Zea mays
There is increasing concern in the United States about the pesticide movement in soil, groundwater contamination, and pesticide residue in food. The objective of this study was to determine the efficacy, degradation, and movement of fenamiphos (Nemacur 15G) in the soil and residues in squash fruit as influenced by four simulated rainfall treatments (2.5 or 5.0 cm each applied 1 or 3 days after nematicide application) under field conditions. In 1990, concentrations of fenamiphos were greater in the top 15 cm of soil in plots with no rainfall than in those treated with rainfall. Eighty to 95 % of the fenamiphos recovered from treated plots was found in the 0-15-cm soil layer. The concentration of fenamiphos recovered from the 0-15-cm soil layer in 1991 was approximately one-half the concentration recovered in 1990, but greater concentrations of fenamiphos sulfoxide (an oxidation product of fenamiphos) were recovered in 1991 than in 1990. Concentrations of fenamiphos, fenamiphos sulfoxide, and fenamiphos sulfone were near or below detectable levels (0.002 mg/kg soil) below the 0-15-cm soil layer. Rainfall treatments did not affect the efficacy of the nematicide against Meloidogyne incognita race 1. The concentration of fenamiphos in squash fruit in 1991 was below the detectable level (0.01 mg/kg).
Cucurbita pepo var. melopepo; degradation; efficacy; fenamiphos; leaching; Meloidogyne incognita; nematicide; nematode; pesticide residue; root-knot nematode; squash
Hot-water dips with and without the additives abamectin and sodium hypochlorite were evaluated for control of Ditylenchus dipsaci infection of garlic seed cloves. All treatments were compared to hot water-formalin clove dip disinfection and to nontreated infected controls for garlic emergence, midseason infection, bulb damage, and yield at harvest in field plots in 12 experiments. Hot-water treatments without additives only partially controlled D. dipsaci when a warming presoak dip (38 C) of 30, 45, or 60 minutes' duration was followed by a hot-water dip (49 C) of 15-30 minutes' duration. Exposure to 49 C for 30 minutes caused slight retardation of garlic emergence, although normal stand was established. Abamectin at 10-20 ppm as the 20-minute hot dip (49 C) or as a 20-minute cool dip (18 C) following a 20-minute hot-water dip and sodium hypochlorite at 1.052-1.313% aqueous solution as the 20-minute hot dip were highly effective in controlling D. dipsaci and were noninjurious to garlic seed cloves. None of these treatments was as effective as a hot water-formalin dip and were noneradicative, but showed high efficacy on heavily infected seed cloves relative to nontreated controls. Abamectin was most effective as a cool dip. These abamectin cool-dip (following hot-water dip) and sodium hypochlorite hot-dip treatments can be considered as effective alternatives to replace formalin as a dip additive for control of clove-borne D. dipsaci. Sodium hypochlorite was less effective as the cool dip, and at concentrations of 1.75-2.63% was phytotoxic to garlic.
abamectin; Allium sativum; Ditylenchus dipsaci; formaldehyde; garlic; hot-water dip; seed-borne infection; sodium hypochlorite; stem nematode
Many new cultivars of soybean (Glycine max) are released each year. Knowledge of their relative susceptibility to soybean cyst nematode (Heterodera glycines) is of interest to soybean breeders and those making nematode management recommendations. Two-hundred-eighty-one cultivars and breeding lines of soybean were screened for resistance to isolates of H. glycines races 1, 2, 3, 4, 5, 6, 9, and 14. No cultivar or line (except possibly PI 437654 or cultivars developed from this PI line) had resistance to all of the races tested. Twenty-one cultivars and lines were resistant to race 1, 5 to race 2, 146 to race 3, 2 to race 4, 4 to race 5, 24 to race 6, and 24 to race 14; some had resistance to more than one race. In addition, several cultivars and lines had moderate resistance to each of the race isolates tested.
breeding; cultivar; Glycine max; Heterodera glycines; soybean; soybean cyst nematode; race; resistance