Transfer and Development of Pasteuria penetrans

Pasteuria penetrans isolate P-20 has been attributed as the cause of soil suppressiveness to peanut root-knot nematode in Florida. In this study, P. penetrans was transferred from a suppressive site to a new site and established by growing susceptible hosts to the peanut root-knot nematode during both summer and winter seasons. When two soil fumigants, 1,3-dichloropropene (1,3-D) and chloropicrin, were applied broadcast at the rate of 168 liters/ha and 263 kg/ha, respectively, the bacterium was not adversely affected by 1,3-D but was adversely affected by chloropicrin. In autumn 2005, after the harvest of the second peanut crop, the greatest number of J2 was recorded in the chloropicrin-treated plots, followed by the non-fumigated plots and 1,3-D-fumigated plots. The percentage J2 encumbered with endospores, endospores per J2 and percentage of P. penetrans-infected females were greatest in the non-fumigated plots, followed by 1,3-D- and chloropicrin-fumigated plots. This study demonstrates that P. penetrans can be transferred from a suppressive site to a new site and increased to suppressive densities against the peanut root-knot nematode.     

Preplant Fumigation for Citrus Nematode Control in Florida

Preplant soil fumigation experiments were conducted to control the citrus nematode, Tylenchulus semipenetrans. Generally, D-D (1,3-dichloropropene, 1,2-dichloroptopane and related chlorinated C₃-hydrocarbons), Telone (1,3-dichloropropene and related chlorinated C₃-hydrocarbons), Telone PBC (80% 1,3-dichloropropene, 15% chloropicrin, 5% propargyl bromide), and EDB (ethylene dibromide) controlled T. semipenetrans effectively for 4 years. The trials involved four scion varieties, two rootstock varieties and three soil types. Tree growth and yield were increased with application of D-D at 374 or 561 liters/ha (40 or 60 gal/acre) or Telone at 299 or 449 liters/ha (32 or 48 gal/acre) in broadcast and strip treatments.     

Pinto Bean Yield Increased by Chemical Control of Pratylenchus spp.

Pinto bean yields and Pratylenchus spp. (nematode) population densities are reported for field plots pro-plant treated with nematicides in 1966 and 1968. Vidden-D (1,3-dichloropropene, 1,2-dichloropropane and related chlorinated hydrocarbons), Vortex (20% methyl isothioeyanate plus 80% chlorinated Ca-hydrocarbons), Telone PBC (80% dichloropropenes, 15% chloropicrin, and 5% propargyl bromide), Dasardt (0,0-Diethyl 0-[p-(methylsulfmyl)phenyl] phosphorothioate, and Dowfume MC-2 (98% methyl bromide plus 2% chloropierin) were used in 1966. Vorlex, Dasanit, and D-D (1,3-dichloropropene, 1,2-dichloropropane and related chlorinated hydrocarbons) were each used at two rates in 1968.Fumigated plot yields ranged 32-56% higher than control plots in 1966 and 11-80% higher in 1968. Significant yield increases were obtained for all fumigants except Telone PBC in 1966. In 1968 significant increases were obtained from use of the high rate (374 liters/ha) of Vorlex and low rate (8.4 liters/ha) of Dasanit. There was an inverse relationship between yield and numbers of Pratylenchus spp./g root on four sampling dates in 1968. A correlation coefficient of -.39 (P ≤ 0.05) was obtained for samples taken 36 days after planting and -.52 (P ≤ 0.01) for samples taken 30 days later. There was no significant correlation between yield and numbers of Pratylenchus spp. recovered from the soil.     

Effect of Aldicarb,Ethoprop, and Carbofuran on Control of Coffee Root-knot Nematode,Meloidogyne exigua

Egg hatch of Meloidogyne exigua was significantly inhibited in 14 days pretreatment with aldicarb, ethoprop, or carbofnran at concentrations higher than 0.1 μg/ml; these eggs were found to delay hatch in 19 days posttreatment in ethoprop. Aldicarb and carbofuran solutions at concentrations greater than 0.1 μg/ml significantly decreased the motility and the life span of the second-stage juveniles; aldicarb was more toxic than carbofuran to the nematode. In a field test, aldicarb (Temik 10G), ethoprop (Mocap 10G), and carbofuran (Furadan 5G and Furadan Liquid 350F) significantly decreased M. exigua populations.     

Control of Heterodera carotae,Ditylenchus dipsaci,and Meloidogyne javanica with Fumigant and Nonfumigant Nematicides

Five field trials were conducted in Italy in 1983 and 1984 to test the efficacy of isazofos and benfuracarb in controlling Heterodera carotae on carrot, Ditylenchus dipsaci on onion, and Meloidogyne javanica on tomato. Methyl isothiocyanate (MIT) was tested against H. carotae and M. javanica. Single (10 kg a.i./ha) and split (5 + 5 kg a.i./ha) applications of isazofos gave yield increases of carrot and onion similar to those obtained with DD (300 liters/ha) and aldicarb (10 kg a.i./ha). Population densities of H. carotae in carrot roots at harvest and of M. javanica in tomato roots 2 months after transplanting were also suppressed by isazofos. Benfuracarb (10 kg a.i./ha increased onion yields in a field infested with D. dipsaci, but it was not effective against H. carotae or M. javanica. The efficacy of MIT at 400 and 600 liters/ha was similar to that of MIT + DD (Di-Trapex) at 300 liters/ha. Both nematicides inhibited hatch of H. carotae eggs and decreased the soil population density of M. javanica.     

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.     

Influence of Edaphic Factors and Previous Crop on Pratylenchus spp. Population Densities in Potato

Root and soil samples from commercial potato fields were assayed for nematodes in 1983 and 1984. Pratylenchus spp. population densities in Suffolk County, New York, were consistently, though not always statistically, higher in potato fields that had been planted to rye or wheat rather than potatoes during the previous growing season. Regardless of the previous crop, population densities in the two potato production areas in Suffolk County differed significantly: population densities on the south fork were 1.9-5.5 times higher than those on the north fork. Species prevalence differed significantly on the two forks but was not related to the previous year''s crop. P. penetrans and P. crenatus were found primarily on the north and south forks, respectively. Differences in species distribution were associated with differences in soil types. P. crenatus was usually found on loams and silt loams, but P. penetrans was found more frequently on sandy soils.     

Soybean Yield as Related to Rates of 1,3-Dichloropropene Applied at Planting for Management of Root-Knot Disease

1,3-Dichloropropene (1,3-D) at rates of 17.2 to 51.6 liters/ha applied 3 days preplant or at planting significantly (P < 0.05) reduced the amount of galling on roots of soybean grown in sites infested with Meloidogyne incognita or M. arenaria. Populations of M. incognita second-stage juveniles at harvest were significantly (P < 0.05) reduced by all treatments. Only the 51.6-liters/ ha treatments and a 3-day preplant 34.4-liters/ha application significantly reduced at-harvest juvenile infestations of M. arenaria. Equations (P < 0.001) relating soybean yield and 1,3-D dosage indicated soybean phytotoxicity at the upper range of the nematicide rates. The maximum yield response was predicted at 40 liters/ha applied 3 days preplant at both infestation sites. Maximum yield response was predicted with 30 liters/ha applied at planting to M. incognita-infested soil and from 25 liters/ha applied at planting to M. arenaria-infested soil. Application of economic factors suggested that management of M. incognita may be cost effective with at-plant treatments of low rates of 1,3-D. Yield responses of M. arenaria-infected soybean exposed to similar treatments were insufficient to justify their use at prevailing prices.     

Relationship Between Population Densities of Pratylenchus penetrans and Crop Losses in Flue-Cured Tobacco in Ontario

Flue-cured tobacco was grown in microplots consisting of concrete drainage tries, 40-cm (i.d.), infested with 0; 666 ; 2000; 6000 or 18,000 root-lesion nematodes, Pratylenchus penetrans/kg of soil. Yield and grade index decreased with preplant soil population densities in excess of 2000/kg of soil. At initial densities of 6000 and 18,000/kg of soil losses in crop returns were 11.0% and 27.5%, respectively. Decreases in the maturity index and in percentage dry stalk weight with increasing densities showed that the nematode delayed maturity. Increases in population densities of nematodes were correlated with decreases in weights of tops and roots and in plant height. All final population densities in soil were lower than the initial densities except at the lowest pre-plant density. All soil populations at midseason were lower than those at the beginning and end of the growing season. Populations of P. penetrans at harvest were in excess of half a million per root system with the 18,000/kg initial soil population density. The results suggest that fumigation, which costs $75/ha, or approximately 2% of the crop value, is economically warranted at preplant densities in excess of 2000/kg of soft.     

Effects of Application Strategies of Fumigant and Nonfumigant Nematicides on Cantaloupe Grown in Deep Sand Soils in Florida

A 2-year study was conducted in which three treatment tactics of oxamyl (at planting application, application every 2 weeks, and rescue applications, as determined by crop symptoms) were compared to fumigant treatments with methyl bromide, 1,3-dichloropropene (1,3-D), and 1,3-D plus chloropicrin for management of Meloidogyne spp. In 2002, treatments that included 1,3-D produced higher yields as determined both by number and weight of marketable fruit. All treatment tactics relying solely on oxamyl, at planting, scheduled treatments, and rescue, were not different from untreated controls for both marketable yield and number of fruit. Gall ratings in 2002 were lowest for 1,3-D at the 112-liters/ha rate, followed by 1,3-D at 84 liters/ha with and without oxamyl. All treatments of oxamyl, except when combined with 1,3-D, had gall ratings not different from untreated plots. In 2004, treatments of methyl bromide and 1,3-D plus chloropicrin had the highest total number of both marketable fruit and highest marketable yields. All treatment strategies relying solely on oxamyl had yields equivalent to the untreated controls. Mean root-gall ratings were lowest for methyl bromide plus chloropicrin and 1,3-D plus chloropicrin treatments. Root-gall ratings for all treatment tactics relying solely on oxamyl were not different from untreated controls.     

Pratylenchus penetrans Population Dynamics on Three Potato Cultivars

Reproduction of Pratylenchus penetrans on the potato cultivars Hudson, Katahdin, and Superior was determined in greenhouse and field microplot experiments. Although all three cultivars were good hosts for P. penetrans, differences in reproductive rate were found. In one greenhouse experiment, Katahdin plants inoculated with 1,500 or 15,000 P. penetrans per pot had larger population densities at harvest than did Superior; however differences between these cultivars were not significant in three other greenhouse experiments. In another experiment, population densities of P. penetrans on Hudson did not differ from those on Katahdin and Superior when inoculated with 270 and 5,080 nematodes per pot after 45 days in the greenhouse. However, population densities were usually higher on Hudson and Katahdin than on Superior in field microplots at four initial population densities during two seasons. Higher population densities on Hudson were detectable 304 days after planting in one of the two microplot studies. The juvenile:female and the male:female ratios were sometimes larger on Katahdin than on Superior, but differences were inconsistent. There was no evidence of resistance in the three cultivars evaluated, but reproduction was generally highest on Hudson and lowest on Superior.     

Effect of Ditylenchus dipsaci and Pratylenchus penetrans on Verticillium Wilt of Alfalfa

Verticillium albo-atrum wilt symptoms appeared faster and were significantly more severe in the presence of Ditylenchus dipsaci in Vernal, a wilt-susceptible cultivar, than in Marls Kabul, a wilt-resistant cultivar. Winter kill in the field was not affected by the nematode during the first winter, but 50% of plants were killed in the second winter. Forage yield from nematode-infected plants was significantly reduced the second year. Interaction with V. albo-atrum did not significantly reduce forage yields below that of D. dipsaci alone. Pratylenchus penetrans did not increase the severity of wilt symptoms in the presence of V. albo-atrum, nor did it affect forage yield in the greenhouse. It did, however, reduce alfalfa yields in presence of V. albo-atrum under field conditions. D. dipsaci and P. penetrans reproduced faster in Vernal than in Maris Kabul when the fungus was present.     

Suppression of Meloidogyne arenaria Race 1 by Soil Application of Endospores of Pasteuria penetrans

The potential of Pasteuria penetrans for suppressing Meloidogyne arenaria race 1 on peanut (Arachis hypogaea) was tested over a 2-year period in a field microplot experiment. Endospores of P. penetrans were mass-produced on M. arenaria race 1 infecting tomato plants. Endospores were inoculated in the first year only at rates of 0, 1,000, 3,000, 10,000, and 100,000 endospores/g of soil, respectively, into the top 20 cm of microplots that were previously infested with M. arenaria race 1. One peanut seedling was planted in each microplot. In the first year, root gall indices and pod galls per microplot were significantly reduced by 60% and 95% for 100,000 endospores/g of soil, and 20% and 65% for 10,000 endospores/g of soil, respectively. Final densities of second-stage juveniles (J2) in soil were not significantly different among the treatments. The number of endospores attached to J2 and percentage of J2 with attached endospores significantly increased with increasing endospore inoculation levels. Pasteuria penetrans significantly reduced the densities of J2 that overwintered. In the second year, root and pod gall indices, respectively, were significantly reduced by 81% and 90% for 100,000 endospores/g of soil, and by 61% and 82% of 10,000 endospores/g of soil. Pod yields were significantly increased by 94% for 100,000 and by 57% for 10,000 endospores/g of soil, respectively. The effect of P. penetrans on final densities of J2 in soil was not significant. Regression analyses verified the role of P. penetrans in the suppression of M. arenaria. The minimum number of endospores required for significantly suppressing M. arenaria race 1 on peanut was 10,000 endospores/g of soil.     

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.     

Population Trends and Vertical Distribution of Plant-Parasitic Nematodes Associated with Vitis labrusca L. in Michigan

Nematode population trends and vertical distribution were monitored in a southwest Michigan vineyard (Vitis labrusca cv. Concord) from 1976 through 1983. Shallow (20 cm) and deep (90 cm) applications of 1,3-dichloropropene applied at 281 (shallow) plus 658 or 1,122 (deep) liters/ ha provided excellent control of Xiphinema americanum, Criconemella xenoplax, and Meloidogyne hapla. Populations of X. americanum remained below detectable levels for the entire 8-year experimental period where the fumigant was applied. X. americanum and C. xenoplax populations exhibited multiyear cycling in nonfumigated plots. M. hapla was first detected in 1978 and increased in prominence from 1980 through 1982. Criconemella spp. were commonly parasitized by an endoparasitic fungus. Parasitism was monitored and reported as an indication of nematode population quality.     

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.     

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.     

Control of Meloidogyne spp. on Russet Burbank Potato by Applying Metham Sodium through Center Pivot Irrigation Systems

Metham sodium applied in October through center pivot irrigation systems was evaluated for control of Meloidogyne hapla at 374, 468, and 701 liters/ha and for control of M. chitwoodi at 468 liters/ha on potato. Metham sodium at the high rates effectively controlled M. hapla. No females were detected in the tubers at the high rates of nematicide application, whereas a mean of 19 and 69% of the tubers were infected at the low rate and in the nontreated controls, respectively. In the M. chitwoodi trial only 1.5% of the tubers in the treated plots were infected compared with 82% in the nontreated plots. Metham sodium effectively controlled M. chitwoodi to soil depths of 30, 61, and 91 cm.     

Effects of Soil pH on Reproduction of Pratylenchus penetrans and Forage Yield of Alfalfa

''Vernal'' alfalfa was grown for 30 weeks in nematode-free soil and in soil infested with Pratylenchus penetrans. Charlottetown fine sandy loam soil was used at its pH of 4.4 and at adjusted reactions of 5.2, 6.4 and 7.3. Nematode reproduction was significantly greater at pit 5.2 and 6.4 and was not related to alfalfa root production over the full pH range studied. A significant nematode infestation X soil pit interaction on forage yield was recorded. Nematode infestation significantly decreased forage yields at ptt 5.2 and 6.4 but not at pH 4.4 and 7.3.     

Effects of Potassium Fertilization and Pratylenchus penetrans on Yield and Potassium Content of Red Clover and Alfalfa

Red clover and alfalfa were inoculated with Pratylenchus penetrans and grown in an Alberry sandy loam soil to which potassium (K⁺) was added at seeding at 0, 41.5, 83, and 166 μg/g. In one experiment with alfalfa, additional K⁺ was added after each forage cut to replace that which was removed. Nematode populations were not consistently affected by K⁺ fertilization. Nematode infection stunted red clover and alfalfa and resulted in lower yields at all K⁺ levels, except for alfalfa at the lowest K⁺ level. Nematode infection had no effect on taproot yields. However, it resulted in lower rootlet yields from red clover at all K⁺ levels, lower rootlet yields from alfalfa only at the highest K⁺ level in one experiment, and lower rootlet yields at all but the lowest K⁺ level in a second experiment, potassium fertilization enhanced yield of red clover and alfalfa. Yield increases were smaller from increased K⁺ fertilization in nematode-infested soil than in noninfested soil. Pralylenchus penetrans had little effect on the K⁺ content of red clover or alfalfa. The stunting of plants from nematode infection resulted in less K⁺ being removed from the soil.