Growth of Carrot and Tomato from Oxamyl-coated Seed and Control of Meloidogyne hapla

Oxamyl was coated on carrot (Daucus carota L. cv. Spartan Fancy-80) and tomato (Lycopersicon esculentum Mill. cv. Glamour) seeds with a polymer sticker for the control of Meloidogyne hapla. The sticker diluted in water 1:1 delayed carrot seedling emergence. Oxamyl at 40 mg/ml in a 1:5 dilution of sticker lowered the rate of carrot seedling emergence until day 13 and plant growth until day 28. Oxamyl at 20 or 40 mg/ml in a 1:5 dilution of sticker on carrot seeds planted in M. hapla-infested muck soil resulted in fewer galled tap roots and fewer galls per root system 4 weeks after planting. Tap root lengths were greater than those of the control. Tomato seedling emergence was delayed and top and root weights were reduced, relative to the control, at 25 days by the sticker diluted 1:1 to 1:3. Oxamyl at 20 or 40 mg/ml in a 1:5 diluted sticker delayed tomato seedling emergence. Top weights of tomato seedlings from seeds coated with 20 mg/ml of oxamyl in a 1:5 diluted sticker planted in a silt loam were greater than control top weights at 4 and 6 weeks. Root weights were greater than those of the control only at 4 weeks. There were fewer galls per gram of root on seedlings from oxamyl-coated seeds and fewer juveniles per pot of soil, relative to the controls, only at 4 weeks.     

Control of Pratylenchus penetrans and Meloidogyne hapla and Yield Response of Alfalfa Due to Oxamyl Seed Treatments

Alfalfa (Medicago sativa L. cv. Saranac) seed were soaked for 20 minutes in water, acetone, or methanol containing 10 or 50 mg/ml of oxamyl (Vydate L) or coated with a 2% aqueous cellulose solution containing the same amounts of oxamyl. Seed were analyzed for oxamyl by HPLC immediately after treatment and after 9 and 26 months of storage. Oxamyl content of alfalfa seed did not decline after 26 months of storage. The effects of seed treatment on growth of alfalfa and nematode control were examined using soils infested with Pratylenchus penetrans and Meloidogyne hapla. Germination was not affected by any of the seed treatments. Twenty-one days after sowing, the total growth of alfalfa seedlings grown from seed treated with 50 mg/ml of oxamyl in P. penetrans-infested soils had increased by 62% over controls. Nodulation per pot increased by as much as 267%, and the densities of P. penetrans per gram of root were reduced by as much as 73% compared to control plants. In M. hapla-infested soils, increases in plant growth (32%) and nodulation (71%) also occurred with oxamyl-treated seeds. Root gall reduction (86%) was also substantial due to oxamyl seed treatment.     

Biological Control of Meloidogyne hapla on Alfalfa and Tomato with the Fungus Meria coniospora

This study was to determine whether Arthrobotrys flagrans, A. oligospora, and Meria coniospora would control the root-knot nematode Meloidogyne hapla on alfalfa and tomato. Alfalfa seeds were coated with a fungus-rye powder in 2% cellulose and were planted in infested soil. Three-week-old seedlings from seed treated with M. coniospora had 60% and 58% fewer galls in two experiments than did seedlings from untreated seeds. Numbers of J2 in the soil were not reduced. Plant growth did not improve. When seed of tomato were coated with M. coniospora and planted in M. hapla-infested soil, roots had 34% fewer galls and 47% fewer J2 in the soil at 28 days. After 56 days there was no reduction in J2 numbers. Plant growth did not improve. When roots of tomato transplants were dusted with M. coniospora fungus-rye powder or sprayed with a spore suspension before planting in M. hapla-infested soil, 42% and 35%, respectively, fewer galls developed in 28 days on treated roots than on roots not treated with fungus. The numbers of J2 extracted from roots or recovered from soil were not reduced, however, and plant growth did not improve.     

Growth of Potato and Control of Pratylenchus penetrans with Oxamyl-treated Seed Pieces in Greenhouse Studies

Oxamyl was applied to both uncut and cut potato tubers in aqueous solutions of 1,000 to 32,000 μg/ml. Emergence in greenhouse pots was delayed for a day or more after soaking cut tuber pieces in 32,000 μg/ml. After 10 weeks plant growth was greater, relative to the control, when Pratylenchus penetrans-infested soil was planted with cut tubers soaked for 20 minutes in 32,000 μg/ml. Soaking for 40 minutes did not increase nematode control nor affect plant growth. Oxamyl applied to tubers at 1,000 μg/ml reduced the numbers of P. penetrans in the soil by 20% and in the roots by 35%; at 32,000 μg/ml, the numbers of P. penetrans in the soil were reduced by 73-86% and in the roots by 86-97%. The numbers of P. penetrans did not increase in the roots of plants developed from cut tubers soaked in 32,000 μg/ml over a period of 10 weeks, but numbers of lesion nematodes had begun to increase in the soil.     

Coating Soybean Seed with Oxamyl for Control of Heterodera glycines

Oxamyl coated on soybean (Glycine max (L.) Merr. cv. Elgin) seeds in solutions of 20, 40, 80, and 160 mg/ml had no serious deleterious effects on seedling emergence and growth when planted in sterile soil. Seedling emergence on day 3 was less than that of the uncoated control, but by day 7 emergence was equal to, or greater than, the control. Shoot and root growth from seed coated with oxamyl in 40 and 80 mg/ml solutions was greater than that of the control. In soil infested with soybean cyst nematode, Heterodera glycines, shoot weight of soybean plants from seeds coated with oxamyl in 80 mg/ml solution was 11 and 9% greater at weeks 3 and 7, respectively, than from uncoated seeds. Numbers of juveniles (J3 and J4) and adults of H. glycines observed on the roots of plants from oxamyl-coated seeds were 83, 42, and 49% less at weeks 3, 5, and 7, respectively, than numbers on the roots of the untreated control. Numbers of J2 extracted from the roots of plants from oxamyl-coated seeds were 75% less at weeks 5 and 7 than those extracted from roots of uncoated seeds. The numbers of J2 extracted from the soil planted to oxamyl-coated seeds were 51 and 33% less at weeks 5 and 7, respectively, than from soil planted to uncoated seed.     

Effect of Hirsutella rhossiliensis on Infection of Potato by Pratylenchus penetrans

We evaluated the ability of the nematode-pathogenic fungus Hirsutella rhossiliensis (Deuteromycotina: Hyphomycetes) to reduce root penetration and population increase of Pratylenchus penetrans on potato. Experiments were conducted at 24 C in a growth chamber. When nematodes were placed on the soil surface 8 cm from a 14-day-old potato cutting, the fungus decreased the number entering roots by 25%. To determine the effect of the fungus on population increase after the nematodes entered roots, we transplanted potato cuttings infected with P. penetrans into Hirsutella-infested and uninfested soil. After 60 days, the total number of nematodes (roots and soil) was 20 ± 4% lower in Hirsutella-infested than in uninfested soil.     

Interactions Among Selected Endoparasitic Nematodes and Three Pseudomonads on Alfalfa

Meloidogyne hapla, Pratylenchus penetrans, and Helicotylenchus dihystera, reduced the growth of ''Saranac AR alfalfa seedlings when applied at concentrations of 50 nematodes per plant. All except P. penetrans reduced seedling growth when applied at 25 per seedling. M. hapla reduced growth when applied at 12 per seedling. Nematodes interacted with three pseudomonads to produce greater growth reductions than were obtained with single pathogens, suggesting synergistic relationships. Ditylenchus dipsaci, applied at 25 or 50 nematodes per seedling, reduced plant weight compared with weights of control plants, but did not interact with test bacteria. All of the nematodes except D. dipsaci produced root wounds which were invaded by bacteria.     

Influence of Nematodes and Light Sources on Growth and Nodulation of Soybean

The influence of nematodes on nodulation of soybean varied according to their modes of parasitism. In the greenhouse, nodule formation was stimulated by the endoparasites, Meloidogyne hapla and Pratylenchus penetrans, but was inhibited slightly by the ectoparasite, Belonolaimus longicaudatus. In an experiment under controlled conditions in a phytotron, Heterodera glycines severely inhibited nodule formation, whereas plants inoculated with B. longicaudatus and P. penetrans had more nodules per g root than nematode-free plants. Nitrogen-fixing capacity, however, was inhibited by all three nematode species. Different light sources used in the phytotron experiment also influenced growth and nodulation of soybean. A fluorescent plus incandescent light regime resulted in plants with the greatest shoot weight, pod number, and nodules per g root. Plants grown under Lucalox lamps had excessive stem elongation.     

Effect of Single and Interplantings on Pathogenicity of Pratyenchus penetrans and P. neglectus to Alfalfa and Crested Wheatgrass

Alfalfa is a host of Pratylenchus penetrans and P. neglectus, whereas crested wheatgrass is a host of P. neglectus but not of P. penetrans. In a 120-day greenhouse experiment at 24 ñ 3 C, P. neglectus inhibited the growth of ''Lahontan'' alfalfa and ''Fairway'' crested wheatgrass. There were no differences in persistence and plant growth of alfalfa and crested wheatgrass, or reproduction of P. neglectus, in single plantings of alfalfa (AO) or crested wheatgrass (CWO), or in interplanted alfalfa and crested wheatgrass (ACW) treatments. On alfalfa, P. penetrans inhibited growth and reproduced more than did P. neglectus. Inhibition of plant growth and reproduction of P. penetrans was greater on alfalfa in AO than in ACW treatments. Pratylenchus penetrans did not reproduce on crested wheatgrass, but inhibited growth of crested wheatgrass in interplanted treatments and was avirulent in single planted treatments. Results were similar in a controlled growth chamber experiment at 15, 20, 25, and 30 C. Both nematode species inhibited alfalfa growth at all temperatures, and P. penetrans was more virulent than was P. neglectus to alfalfa at all temperatures and treatments. Plant growth inhibition and reproduction of P. penetrans on alfalfa in single and interplanted treatments were similar at 15-20 C, but were greater in single than in interplanted treatments at 25-30 C. Pratylenchus penetrans was avirulent to crested wheatgrass in the single planted treatments at all temperatures, but inhibited growth of crested wheatgrass in interplanted treatments at 20-30 C. Plant growth and reproduction of P. neglectus on crested wheatgrass was similar in single and interplanted treatments at 20-30 C and 15-30 C, respectively.     

Effect of Application Timing of Oxamyl in Nonbearing Raspberry for Pratylenchus penetrans Management

In 2012, the Washington raspberry (Rubus idaeus) industry received a special local needs (SLN) 24(c) label to apply Vydate L^® (active ingredient oxamyl) to nonbearing raspberry for the management of Pratylenchus penetrans. This is a new use pattern of this nematicide for raspberry growers; therefore, research was conducted to identify the optimum spring application timing of oxamyl for the suppression of P. penetrans. Three on-farm trials in each of 2012 and 2013 were established in Washington in newly planted raspberry trials on a range of varieties. Oxamyl was applied twice in April (2013 only), May, and June, and these treatments were compared to each other as well as a nontreated control. Population densities of P. penetrans were determined in the fall and spring postoxamyl applications for at least 1.5 years. Plant vigor was also evaluated in the trials. Combined results from 2012 and 2013 trials indicated that application timing in the spring was not critical. Oxamyl application reduced root P. penetrans population densities in all six trials. Reductions in P. penetrans population densities in roots of oxamyl-treated plants, regardless of application timing, ranged from 62% to 99% of densities in nontreated controls. Phytotoxicity to newly planted raspberry was never observed in any of the trials. A nonbearing application of oxamyl is an important addition to current control methods used to manage P. penetrans in raspberry in Washington.     

Population Growth of Pratylenchus penetrans on Winter Cover Crops Grown in the Pacific Northwest

Population growth of Pratylenchus penetrans on 13 fall and winter cover crops was studied in the greenhouse and field. All crops except oat cv. Saia supported population growth of P. penetrans in greenhouse experiments, although the response of P. penetrans to oat cv. Saia varied considerably between experiments. The mean ratio of the final population density/initial population density (Pf/Pi) after 16 weeks for P. penetrans added to a greenhouse soil mix was 0.09, whereas Pf/Pi values after 10 weeks for two experiments with naturally infested soil were 0.95 and 2.3. Although P. penetrans increased on sudangrass cv. Trudan 8 and sudangrass × sorghum hybrid cv. SS 222, subsequent incorporation of sudangrass vegetation into soil reduced P. penetrans populations to preplant levels. Field experiments were inconclusive but suggested that oat cv. Saia or rye cv. Wheeler may be better choices for winter cover than weed-contaminated fallow or other crops on P. penetrans-infested sites in the Pacific Northwest.     

Relationship of Ditylenchus dipsaci and Harvest Practices to the Persistence of Alfalfa

Persistence of dormant Ranger and nondormant Moapa alfalfas, both susceptible to Ditylenchus dipsaci, varied with stand age and cutting frequency. Stand reduction increased with cutting frequency. In D. dipsaci-infested soil, stand reductions in Ranger 1, 4, and 5 years old exceeded reductions in stands 2 and 3 years old; persistence was greatest in 2-year-old stands. In Moapa alfalfa, D. dipsaci reduced stands the most in years 2 and 3; whereas persistence was greatest in 1-year-old stands. Harvesting Ranger alfalfa one, two, three, and four times during the growing season reduced 2-year-old stands by 10, 14, 19, and 29% in D. dipsaci-infested soil and by 2, 4, 4, and 7% in uninfested soil, respectively. Comparable reductions in Moapa alfalfa were 13, 16, 18, and 38% in infested soil and 0, 2, 4, and 6% in uninfested soil. Cutting frequency had less effect on persistence of resistant semidormant Lahontan grown in D. dipsaci-infested soil relative to susceptible cultivars. Increasing the number of cuttings per year decreased storage of total nonstructural carbohydrate and adversely affected persistence of alfalfa stands and yields; the greatest negative effects occurred on both resistant and susceptible alfalfa in D. dipsaci-infested soil.     

Damage and Management of Meloidogyne hapla Using Oxamyl on Carrot in New York

The northern root-knot nematode (Meloidogyne hapla) is a major pathogen of processing carrot in New York, significantly reducing marketable yield and profitability. Severely infected carrots are stubby, galled and forked and therefore unmarketable. In field microplot trials in 1996 and 1998, the incidence and severity of root-galling increased and the marketable yield of carrot decreased as the initial inoculum density of M. hapla was increased from 0 to 8 eggs/cm³ soil, in mineral or organic soils. The application of oxamyl at planting was effective against M. hapla and its damage to carrots grown in mineral and organic soils. Oxamyl application reduced root-galling severity and increased marketable yield. In commercial fields, the cost-effectiveness of oxamyl application was related to the level of soil infestation with M. hapla.     

Hirsutella rhossiliensisand Verticillium chlamydosporium as Biocontrol Agents of the Root-knot Nematode Meloidogyne hapla on Lettuce

Hirsutella rhossiliensis and Verticillium chlamydosporium infected second-stage juveniles (J2) and eggs of Meloidogyne hapla, respectively, in petri dishes and in organic soil in pots planted to lettuce in the greenhouse. In vitro, H. rhossiliensis produced 78 to 124 spores/infected J2 of M. hapla. The number of J2 in roots of lettuce seedlings decreased exponentially with increasing numbers of vegetative colonies of H. rhossiliensis in the soil. At an infestation of 8 M. hapla eggs/cm³ soil, 1.9 colonies of H. rhossiliensis/cm³ soil were needed for a 50% decrease in J2 penetration of lettuce roots. Egg-mass colonization with V. chlamydosporium varied from 16% to 43% when soil was infested with 8 M. hapla eggs and treated with 5,000 or 10,000 chlamydospores of V. chlamydosporium/cm³ soil. This treatment resulted in fewer J2 entering roots of bioassay lettuce seedlings planted in the infested soils after harvesting the first lettuce plants 7 weeks after infestation with M. hapla. Hirsutella rhossiliensis (0 to 4.3 colonies/cm3 soil), V. chlamydosporium (500 to 10,000 chlamydospores/cm3 soil), or their combination, added to organic soils with 8 M. hapla eggs/cm³ soil, generally did not affect lettuce weight, root galling, or egg production of M. hapla. However, when lettuce was replanted in a mix of infested and uninfested soil (1:3 and 1:7, v:v), egg production was lower in soils with V. chlamydosporium than in soils without the fungus. Both fungi have potential to reduce the M. hapla population, but at densities below 8 eggs/cm³ soil.     

Effect of Foliar Application of Carbofuran and a Related Compound on Plant-parasitic Nematodes under Greenhouse and Growth Chamber Conditions

Greenhouse and growth chamber studies were made to investigate the downward systemic nematicidal activity of carbofuran and its analog 2,3-dihydro-2,2-dimethyl-7-benzofuranyl [(di-n-butyl)-4-aminosulfenyl] carbamate against Meloidogyne incognita, Tylenchorhynchus claytoni, and Pratylenchus penetrans. Oxamyl was used as standard in tests with T. claytoni. Both carbofuran and its analog reduced all three plant-parasitic species when plant foliage was sprayed with chemical suspension of 1,200, 2,400 or 4,800 ppm. The studies show that fewer chemical applications were required to reduce populations of P. penetrans than to reduce populations of T. claytoni. Oxamyl was somewhat less active than either carbofuran or its analog.     

Seasonal Populations of Pratylenchus penetrans and Meloidogyne hapla in Strawberry Roots

Strawberry roots were sampled through the year to determine the populations and distribution of Pratylenchus penetrans and Meloidogyne hapla. Three strawberry root types were sampled—structural roots; feeder roots without secondary tissues; and suberized, black perennial roots. Both lesion and root-knot nematodes primarily infected feeder roots from structural roots or healthy perennial roots. Few nematodes were recovered from soil, diseased roots, or suberized roots. Lesion nematode recovery was correlated with healthy roots. In both 1997 and 1998, P. penetrans populations peaked about day 150 (end of May) and then declined. The decline in numbers corresponded to changes in total strawberry root weight and root type distribution. The loss of nematode habitat resulted from loss of roots due to disease and the transition from structural to suberized perennial roots. Meloidogyne hapla juvenile recovery peaked around 170 days (mid June) in 1997 and at 85, 147, 229, and 308 days (late March, late May, mid August, and early November, respectively) in 1998. There appear to be at least four generations per year of M. hapla in Connecticut. Diagnostic samples from an established strawberry bed may be most reliable and useful when they include feeder roots taken in late May.     

Differential Reaction of Alfalfa Cultivars to Meloidogyne hapla and M. chitwoodi Populations

Meloidogyne hapla reproduced and suppressed growth (P < 0.05) of susceptible Lahontan and Moapa alfalfa at 15, 20, and 25 C. At 30 C, resistant Nevada Syn XX lost resistance to M. hapla. M. hapla invaded and reproduced on Rhizobium meliloti nodules of Lahontan and Moapa, inducing giant cell formation and structural disorder of vascular bundles of nodules without disrupting bacteroids. At 15, 20, and 25 C a M. chitwoodi population from Utah reproduced on Lahontan, Moapa, and Nevada Syn XX alfalfa, suppressing growth (P < 0.05). Final densities of the Utah M. chitwoodi population were greater (P < 0.05) than those of Idaho and Washington State populations on Lahontan at 15 and 25 C and on Nevada Syn XX at 15 C, but were less consistent and smaller (P < 0.05) than those of M. hapla on Lahontan and Moapa at 20 and 25 C. Inconsistent reproduction of the Utah M. chitwoodi population on alfalfa suggests the possible existence of nematode strains revealed by variability in alfalfa resistance. No reproduction or inconsistent final nematode population densities with no damage were observed on Lahontan, Moapa, and Nevada Syn XX plants grown in soil infested with Idaho and Washington State M. chitwoodi populations.     

Suppression of Alfalfa Growth by Concommitant Populations of Pratylenchus penetrans and two Fusarium species

Growth of alfalfa (Medicago sativa cv. Vernal) seedlings was compared after inoculation with combinations of either Pratylenchus penetrans and Fusarium soloni or P. penetrans and F. oxysporum f. sp. medicaginis. A synergistic disease interaction occurred in alfalfa when F. oxysporum and P. penetrans were added simultaneously to the soil. Alfalfa growth was suppressed at all inoculum levels of P. penetrans and F. oxysporum, but not with F. solani. Seedlings inoculated with the nematode alone gave lower yields than when inoculated with either Fusarium species alone. Fusarium oxysporum, but not F. solani, was pathogenic to alfalfa under similar experimental conditions. Fusarium oxysporum did not alter the populations of P. penetrans in alfalfa roots, whereas the presence of F. solani was associated with a diminished number of P. penetrans in the roots.     

Differential Response of Thor Alfalfa to Meloidogyne chitwoodi Races and M. hapla

Second-stage juveniles (J2) of races 1 and 2 of Meloidogyne chiiwoodi and M. hapla readily penetrated roots of Thor alfalfa and Columbian tomato seedlings; however, few individuals of M. chitwoodi race 1 were able to establish feeding sites and mature on alfalfa. Histopathological studies indicate that J2 of race 1 either failed to initiate feeding sites or they caused cell enlargement without typical cell wall thickening. The protoplasm of these cells coagulated, and juveniles of race 1 did not develop beyond the swollen J2 stage. A few females of race 1 fed on small giant cells and deposited a few eggs at least 20 and 30 days later than M. chitwoodi race 2 and M. hapla, respectively. Failure of race 1 to establish feeding sites was related to egression of J2 from the roots. The M. chitwoodi race 1 J2 egression from alfalfa roots was higher than egression of race 2 and M. hapla. Egression of J2 of M. chitwoodi races 1 and 2 from tomato roots was similar and higher than that of M. hapla. Thus egression plays an important role in the host-parasite relationship of M. chitwoodi and alfalfa.     

Effect of Initial Nematode Population Density on the Interaction of Pratylenchus penetrans and Verticillium dahliae on 'Russet Burbank' Potato

Four similar growth chamber experiments were conducted to test the hypothesis that the initial population density (Pi) of Pratylenchus penetrans influences the severity of interactive effects of P. penetrans and Verticillium dahliae on shoot growth, photosynthesis, and tuber yield of Russet Burbank potato. In each experiment, three population densities of P. penetrans with and without concomitant inoculation with V. dahliae were compared with nematode-free controls. The three specific Pi of JR penetrans tested varied from experiment to experiment but fell in the ranges 0.8-2.5, 1.8-3.9, 2.1-8.8, and 7.5-32.4 nematodes/cm³ soil. Inoculum of V. dahliaewas mixed into soil, and the assayed density was 5.4 propagules/gram dry soil. Plants were grown 60 to 80 days in a controlled environment. Plant growth parameters in two experiments indicated significant interactions between P. penetrans and V. dahliae. In the absence of V. dahliae, P. penetrans did not reduce plant growth and tuber yield below that of the nematode-free control or did so only at the highest one or two population densities tested. In the presence of K dahliae, the lowest population density significantly reduced shoot weight and photosynthesis in three and four experiments, respectively. Higher densities had no additional effect on shoot weight and caused additional reductions in photosynthesis in only one experiment. Population densities of 0.8 and 7.5 nematodes/cm³ soil reduced tuber yield by 51% and 45%, whereas higher densities had no effect or a 15% additional effect, respectively. These data indicate that interactive effects between P. penetrans and V. dahliae on Russet Burbank potato are manifested at P. penetrans population densities less than 1 nematode/cm³ soil and that the nematode population density must be substantially higher before additional effects are apparent.