Effects of fumigant nematicides on yield and quality of paste tomatoes grown in southwestern ontario.

Field trials were conducted at the Delhi Research Station, Ontario, Canada, on a Fox loamy sand soil during 1987 and 1988 to evaluate the effects of row application of the fumigants Telone II, Telone C-17, Vorlex Plus, and Vorlex Plus CP on the yield and quality of paste tomato (Lycopersicon esculentum Mill. cv. Ferry Morse 6203). The four fumigants were equally effective in controlling the natural field populations of root lesion nematodes (Pratylenchus penetrans Cobb). A significant reduction in marketable red fruit yield due to different nematode densities at time of transplanting was observed in 1988. Fumigation did not significantly affect the yield of nonmarketable fruit, the relative maturation rate, or the processing quality in either year.

Effect of Oxamyl Treatment of Potato Seed Pieces on Pratylenchus penetrans and Yield.

In the first 2 years of a 3-year (1987-89) microplot study, aqueous solutions of oxamyl (32 mg/ml) were applied to cut potato (Solanum tuberosum cv. Russet Burbank) tubers, grown in fine sandy loam infested with Pratylenchus penetrans. The seed-piece treatment alone and the seed-piece treatment followed by three foliar sprays generally reduced (P = 0.05) population densities of P. penetrans in the soil at midseason and in the soil and roots at harvest, compared to the control. In 1989, all seed pieces treated with oxamyl at 96 mg/ml or at 32, 64, and 96 mg/ml followed by a polymer sticker : water (1:4) dip failed to emerge. Only oxamyl at 64 mg/ml reduced (P = 0.05) midseason soil population densities of P. penetrans. A pre-plant soil treatment with 1,3-D reduced (P = 0.05) numbers of P. penetrans at planting each year and increased (P = 0.05) tuber yields in 1988 and 1989 compared to the control. In 1989, tuber yields from the sticker treatment and the oxamyl seed-piece treatment at 64 mg/ml were lower (P = 0.05) than those in the 1,3-D treatment and similar to those from the untreated control, possibly because of phytotoxicity. Oxamyl treatment of potato seed pieces to control P. penetrans does not appear practical for field production.

Reproduction and Parasitism of Pratylenchus neglectus on Potato.

An initial density (Pi) of 1,540 Pratylenchus neglectus/kg soil suppressed shoot growth of potato, Solanum tuberosum cv. Russet Burbank, in a greenhouse test at 3 weeks. After 6 weeks, shoot weights were reduced by Pi of 662 and 1,540 nematodes/kg soil, the final soil densities of P. neglectus were twice the respective Pi, and the numbers of nematodes per gram dry root were 5,363 and 7,981. In 1986-88 field microplot experiments with the Norchip cultivar, neither shoot nor root weight was suppressed by P. neglectus. In 1986 a Pi of 115 nematodes/kg soil suppressed the total number and weight of tubers per plant. In 1987 a Pi of 186 nematodes/kg soil suppressed the marketable and total number of tubers by 19 and 25 %, respectively. In 1988 a Pi of 1,884 nematodes/ kg soil reduced total and marketable weight by 18 and 19%, respectively. In 1986 and 1987 nematode population densities in the soil increased 34-fold and 27-fold, respectively. In 1988 the Pi of 1,884 nematodes/kg soil rose to 21,890/kg at midseason, then dropped to 4,370/kg at harvest. These studies show for the first time that P. neglectus reproduces well on potato and can cause yield losses. Because of its distribution and abundance, P. neglectus may be considered an economically important parasite of potato in Ontario.

Effects of Fumigant and Nonfumigant Nematicides on Pratylenchus penetrans and Yield of Potato.

In 1984-85 metham-sodium and the combination of 1,3-dichloropropene plus aldicarb decreased (P = 0.05) soil population densities of Pratylenchus penetrans at planting, midseason, and at harvest relative to the untreated control. These treatments increased (P = 0.05) marketable potato tuber yield from 27% to 46% in 1984 and from 23% to 37% in 1985, as compared with the control. In 1984 oxamyl (10% granular and 24% liquid) applied immediately after planting increased (P = 0.05) only the total yield; oxamyl applied 2 weeks after planting failed to control P. penetrans and to increase total or marketable yields. Oxamyl (10 G) applied 2 weeks after planting decreased (P = 0.05) Pf. In 1985 oxamyl (10 G) reduced (P = 0.05) P. penetrans population densities at midseason and harvest, whereas oxamyl (24 L) reduced only harvest population densities. In 1985 neither formulation of oxamyl increased tuber yield.

Control of Pratylenchus penetrans on Potato with Metam-sodium Applied in Irrigation Water.

In 1986, metam-sodium broadcast at 152, 76, 38, 19, and 9.5 kg a.i./ha suppressed the population density of 19,600 Pratylenchus penetrans/kg soil at planting by 100, 90, 63, 23, and 14%, respectively, and in 1987, with 1,370 P. penetrans/kg soil, by 99, 88, 57, 11, and 1%. At harvest, soil population densities increased 2.2-fold in 1986 and 13.9-fold in 1987. Rate of population increase was similar at all rates of nematicide except it was slower at 152 kg a.i./ha in 1987. In both years, shoot and root weights did not differ (P = 0.05). In 1986 the number of tubers in plots treated with 76 and 152 kg metam-sodium a.i./ha and the marketable tuber weight at the three highest rates did not differ significantly from the untreated control. However, 76 and 152 kg a.i./ha resulted in larger numbers of tubers relative to the three lowest rates of metam-sodium and in higher tuber weight relative to the two lowest rates. Yield differences were not statistically significant in 1987, probably because of low infestation levels.

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 mug/ml. Emergence in greenhouse pots was delayed for a day or more after soaking cut tuber pieces in 32,000 mug/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 mug/ml. Soaking for 40 minutes did not increase nematode control nor affect plant growth. Oxamyl applied to tubers at 1,000 mug/ml reduced the numbers of P. penetrans in the soil by 20% and in the roots by 35%; at 32,000 mug/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 mug/ml over a period of 10 weeks, but numbers of lesion nematodes had begun to increase in the soil.

Effects of Fumigants and Systemic Pesticides on Pratylenchus penetrans and Potato Yield.

Replicated trials were conducted near Alliston, Ontario, in 1983 and 1984 to evaluate the efficacy of five chemical treatments in controlling the root-lesion nematode Pratylenchus penetrans on potato, Solanum tuberosum cv. Russet Burbank. The fumigants Vorlex, at 55 liters product/ha, and Telone II B, at 75 liters product/ha, were more effective in suppressing high initial population densities of 18,320 and 50,880 P. penetrans/kg soil in 1983 and 1984, respectively, than single applications of the systemic pesticides Temik 10 G at 22 kg product/ha, Vydate L at 18 and 9 liters product/ha, and Furadan 10 G at 33 kg product/ha. The combination of Vorlex + Temik resulted in greatest nematode suppression and lowest populations at harvest. In 1983, marketable tuber yield (> 7 cm) in the Vorlex + Temik plots was 20.7 t/ha, compared to 4.7 t for the untreated check. Vorlex alone and Telone II B plots yielded 17.3 and 15.9 t/ha, respectively; Temik with 7.5 t also yielded better than the check. Vydate and Furadan did not influence yields significantly. Total yields differed from the check in all treatments except with Furadan. In 1984, marketable yields ranged from 15.5 t/ha for the Vorlex + Temik treatment to 11.2 for the untreated check, but the differences were not statistically significant. Total yields, however, were significantly increased by the fumigants. The difference in response to chemical treatment in the 2 years was attributed to greater heat stress and lack of supplementary irrigation in 1983.

Reaction of Six Solanum tuberosum Cultivars to Pratylenchus penetrans.

Six potato cultivars - Superior, Yukon Gold, Monona, Norchip, Kennebec, and Russet Burbank - were grown in Tioga loamy sand in tile microplots noninfested or infested with 9,800-11,500 P. penetrans/kg soil. At midseason, soil nematode population densities on Superior potatoes were 39,800/kg compared with 17,500-25,800/kg on the other cultivars. At harvest, 118 or 139 days after planting depending on maturity date, the final soil P. penetrans population density was 24,400/kg with Superior and 34,100-51,500/kg with the other cultivars. No differences occurred in the rate of nematode build-up in soil on the six potato cultivars. The nematode suppressed yield of marketable tubers of Superior by 73% and of Yukon Gold by 25%. Losses for Russet Burbank (61%), Kennebec (55%), Monona (46%), and Norchip (43%) were intermediate.

Simplified cleanup and liquid chromatographic determination of oxamyl residues in potato tubers.

A simple and efficient method is presented for the extraction, cleanup, and liquid chromatographic (LC) determination of oxamyl residues in potato tubers. Samples are extracted with methanol, partitioned into dichloromethane, and cleaned up using Sep-Pak Florisil cartridges. LC determination is performed using a Zorbax PSM 60 size exclusion column with an acetonitrile-water (1 + 9) mobile phase and UV detection at 254 nm. Recovery of oxamyl from spiked control tubers averaged 94.1 and 85.9% at fortification levels of 0.4 and 0.08 micrograms oxamyl/g tuber, respectively. The minimum detectable concentration of oxamyl by this method is 0.01 micrograms/g.

Response of Peach Seedlings to Infection by the Root Lesion Nematode Pratylenchus penetrans under Controlled Conditions.

Twenty-one open pollinated populations of peach rootstock seedlings were evaluated for their response to infection by the root lesion nematode, Pratylenchus penetrans, over a period of 98 days. Nematode-infected peach seedling populations were shorter in plant height and had less shoot weight but more dry root weight than nematode-free controls. Rootstock differences were demonstrated for nematode increase over the 98-day period, and average total numbers of nematodes in soil and roots. Rootstocks were classified into three groups differing in total nematode population levels, ratio of nematode increase, and the number of nematodes per root. The heritable nature of rootstock response to nematodes was evident. Rootstocks showing the lowest response to nematode infection included Tzim Pee Tao, Rutgers Red Leaf, and two progenies of a cross of these two rootstocks.

Effect of Plant Age and Transplanting Damage on Sugar Beets infected by Heterodera schachtii.

Sugar beet (Beta vulgaris L. cv. Monogerm C.S.F. 1971) seeds sown into Vineland fine sandy loam, infested with 15,500 H. schachtii juveniles/pot, showed little growth during an 11-week test in the greenhouse. Seedlings transplanted at 2, 4, and 6 weeks of age had 32, 30, and 31% less top weight and 71, 68, and 59% less root weight, respectively, compared to controls grown in nematode-free soil. Nematode reproduction in both direct-seeded and transplanted sugar beets was limited and related to root weight. Shoot/root ratios were increased by the nematodes in all nematode-infected beets compared to those grown in soil without nematodes. In contrast to seeding or transplanting sugar beets into nematode-infested Vineland fine sandy loam, an inoculation of Beverly fine sandy loam supporting 0 (seeds), 2-, 4-, and 6-week-old sugar beet seedlings with 7,400 juveniles/pot, followed by 11 weeks of growth in the growth-room, resulted in top weight losses of only 13, 3, 18, and 15% and losses in root weight of 44, 38, 36, and 38%, respectively. Nematode reproduction was high and all shoot/root ratios were increased by the nematode compared to the noninoculated controls. These experiments have shown that sugar beets sown into nematode-infested soil are damaged much more heavily by H. schachtii juveniles than seeds inoculated with the nematode immediately following sowing. Results indicate that an increase in tolerance of sugar beets to attack by H. schachtii does not occur beyond the first 2 weeks of growth and that transplanting damage lowers the tolerance of seedlings to nematode attack.

Effect of Age of Alfalfa Root on Penetration by Pratylenchus penetrans.

Penetration by all migratory life stages of Pratylenchus penetrans into roots of alfalfa (Medicago sativa L. cv. Du Puits) was inversely proportional to tissue age. Two-day-old tissue in the root hair zone was penetrated twice as much as 10- or 20-day-old sections of the tap root. Age-related differences were also observed in branch roots; these differences were not affected by increasing the number of nematodes from 1 to 10 per inoculation site, nor by increasing the length of the incubation period from 6 to 96 h. Age-related differences were only significant with 3-wk-old plants, not with 2- and 1-wk-old seedlings. Nematodes entered roots at temperatures from 5 to 30 C with maximum entry at 20 C and minimum at 5 C. At all temperatures, except 5 C, penetration into young tissue (2 days) was significantly greater than into medium (10 days) and old (20 days) tissue. Females and third-stage larvae entered the different-aged root sections 122% and 83%, respectively, more than did males. Two-day-old seedlings of the alfalfa cultivars Vernal, Saranac, and Du Puits were penetrated equally by P. penetrans. Perhaps the inverse relationship between penetration and age of root is, in part, responsible for the increasing resistance or tolerance of plants to nematode damage as they grow older.

Influence of Population Densities of Heterodera schachtii on Sugar Beets Grown in Microplots.

High initial population densities of Heterodera schachtii larvae (36 and 108/gm of soil) greatly retarded the seedling emergence of sugar beet 'Monogerm CSF 1971' in Vineland fine sandy loam. In comparison with controls, initial population densities (P(i)'s) of 1.7, 3.0, 6.2, and 14.4 larvae/gm of soil respectively reduced the weight of storage roots by 38, 56, 64, and 92%. Weights of tops also decreased with increases in P(i); weights of tap and small feeder roots tended to be higher at all P(i)'s except the highest. Sucrose percentage was not affected by any initial nematode density. The populations were lower at midseason than at seeding, and at harvest had increased greatly, with respective populations of 339, 402, 222, and 140 larvae/gm of soil. At harvest, cysts/gm of soil and cysts/gm of root were respectively 4.4 and 72, 6.1 and 99, 6.1 and 191, and 5.8 and 140. The maximum rate of multiplication was 150-200. and maximum density was 400 larvae/gm of soil. The high pathogenicity and multiplication rate of the nematode was attributed to optimum temperature conditions and soil type.

Analysis of crop losses in tomato due to Pratylenchus penetrans.

The effects of Pratylenchus penetrans upon yields of 'Veebrite' tomato were studied at initial soil population densities (P(i)) of 360, 2,010, 4,580, and 14,360 nematodes/kg of soil in 20-cm (i.d.) clay-tile microplots. The lowest P(i) appeared to stimulate fruit production. Higher P(i)'s suppressed fruit production (total weight of marketable tomatoes and numbers of intermediate- and large-sized fruits), in comparison to control yields, the highest P(i) resulted in 38% fewer fruits which weighed 44% less. These losses were at least partly due to a delay in fruit ripening, caused by the nematodes, which did not become apparent until the fourth week. Nematode populations in the soil increased at all but the highest P(i); final populations were around 7,000/kg of soil. Nematode populations in roots ranged from 230-590/gm of root at the completion of the experiment. Nematode control by fumigation would definitely be warranted at soil population densities of 2,000/kg or higher; with 500-2,000/kg, the decision to fumigate would depend on soil type and economic and hiological factors.

Effects of population densities of Meloidogyne hapla on growth and yield of tomato.

Growth and yield of 'Veebrite' tomato were studied in 20-cm (i.d.) clay-tile microplots containing initially 260, 1,840, 6,120, or 27,950 Meloidogyne hapla larvae/kg of soil. Low nematode numbers stimulated, and the highest nematode population suppressed, vegetative plant growth. More tomatoes, with a higher total weight, were harvested from plants infested with 260 and 1,840 nematode larvae at planting than from those with initial densities of 6,120 and 27,950 larvae. At the two highest densities, the cumulative fruit production (weight) was suppressed by 10% and 40%, respectively. The increase in growth and yield at the lower densities appeared to be due to an increase in the size of the root systent. However, at the higher densities, yield was no longer directly related to root weight. The reproduction factor of M. hapla was negatively correlated with initial density; for the lowest and highest initial densities, it was 96X and 7X at midseason, and 354X and 3X at harvest, respectively. The equilibrium density was 63,000 larvae/kg of soil; initial densities larger than 2,000 larvae/kg of soil may require control.

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.