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

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

Effects of Temperature on Pratylenchus neglectus and on Its Pathogenicity to Barley

In a petri-dish study, development of the nematode Pratylenchus neglectus was observed every 4 days, and stage-specific development times were estimated, using a parameter estimation algorithm for a distributed-delay population model. The lower threshold temperature for development of a population of P. neglectus was 7.75 C. Temperatures above 25 C were unfavorable for this population on barley. Total numbers of P. neglectus in barley roots and associated soil in pots were greatest at 25 C and lower at temperatures above and below that level. There was no change in nematode numbers per gram of root as temperature increased between 24 C and 32 C because root weights decreased at higher temperatures. Restricted root mass may contribute to the lower total nematode population levels at higher temperature. Maximum number of nematodes moved through a 2-cm layer of sand on a Baermann funnel at about 20 C; lowest number of nematodes moved at 10 C and 30 C.     

Damage Function and Economic Threshold for Belonolaimus longicaudatus on Potato

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

Field Efficacy of Furfural as a Nematicide on Turf

A commercial formulation of furfural was recently launched in the United States as a turfgrass nematicide. Three field trials evaluated efficacy of this commercial formulation on dwarf bermudagrass putting greens infested primarily with Belonolaimus longicaudatus, Meloidogyne graminis, or both these nematodes, and in some cases with Mesocriconema ornatum or Helicotylenchus pseudorobustus. In all these trials, furfural improved turf health but did not reduce population densities of B. longicaudatus, M. graminis, or the other plant-parasitic nematodes present. In two additional field trials, efficacy of furfural at increasing depths in the soil profile (0 to 5 cm, 5 to 10 cm, and 10 to 15 cm) against B. longicaudatus on bermudagrass was evaluated. Reduction in population density of B. longicaudatus was observed in furfural-treated plots for depths below 5 cm on several dates during both trials. However, no differences in population densities of B. longicaudatus were observed between the furfural-treated plots and the untreated control for soil depth of 0 to 5 cm during either trial. These results indicate that furfural applications can improve health of nematode-infested turf and can reduce population density of plant-parasitic nematodes in turf systems. Although the degree to which turf improvement is directly caused by nematicidal effects is still unclear, furfural does appear to be a useful nematode management tool for turf.     

Relative Efficacy of Selected Volatile and Nonvolatile Nematicides for Control of Meloidogyne incognita on Tobacco

Root-knot nematode control and tobacco yields in plots infested with Meloidogyne incognita and treated with the nonvolatile nematicides, aldicarb, Mocap ®, or Nemacur ® were greater than those on similar plots treated with volatile nematicides such as DD, DD + MENCS, SD14647 or tetrachlorothiophene. Root-knot control and tobacco yields in plots treated with carbofuran or Dasanit ® were eqtual to that obtained with DD + MENCS, but less than that obtained with the other volatile soil nematicides. The most efficient dosage was 3.4 kg/hectare active ingredient for aldicarb and Mocap ® and 10.0 kg/hectare for Dasanit ®. Carbofuran and Nemacur ® were equally as effective at 4.2 kg/hectare as they were at higher dosages. The most efficient dosage of DD and SD14647 was 84 liters/hectare. Aldicarb and Dasanit ® resulted in better nematode control and tobacco yields when incorporated into the top 15-20 cm of soil than when incorporated into the top 5-10 cm of soil. Nemacur ® and Mocap ® performed better when incorporated into the top 5-10 cm of soil, and carbofuran performed better when applied in the seed furrow (placed 15-20 cm deep in a 5-cm band and bedded).     

Host Plant Resistance as an Alternative to Methyl Bromide for Managing Meloidogyne incognita in Pepper

Pre-plant soil fumigation with methyl bromide and host resistance were compared for managing the southern root-knot nematode (Meloidogyne incognita) in pepper. Three pepper cultivars (Carolina Cayenne, Keystone Resistant Giant, and California Wonder) that differed in resistance to M. incognita were grown in field plots that had been fumigated with methyl bromide (98% CH₃Br : 2% CCl₃NO₂ [w/w]) before planting or left untreated. Carolina Cayenne is a well-adapted cayenne-type pepper that is highly resistant to M. incognita. The bell-type peppers Keystone Resistant Giant and California Wonder are intermediate to susceptible and susceptible, respectively. None of the cultivars exhibited root galling in the methyl bromide fumigated plots and nematode reproduction was minimal (<250 eggs/g fresh root), indicating that the fumigation treatment was highly effective in controlling M. incognita. Root galling of Carolina Cayenne and nematode reproduction were minimal, and fruit yields were not reduced in the untreated plots. The root-galling reaction for Keystone Resistant Giant was intermediate (gall index = 2.9, on a scale of 1 to 5), and nematode reproduction was moderately high. However, yields of Keystone Resistant Giant were not reduced in untreated plots. Root galling was severe (gall index = 4.3) on susceptible California Wonder, nematode reproduction was high, and fruit yields were reduced (P ≤ 0.05) in untreated plots. The resistance exhibited by Carolina Cayenne and Keystone Resistant Giant provides an alternative to methyl bromide for reducing yield losses by southern root-knot nematodes in pepper. The high level of resistance of Carolina Cayenne also suppresses population densities of M. incognita.     

Effects of Nematophagous Fungi on Numbers and Death Rates of Bacterivorous Nematodes in Arable Soil

In a series of microcosm experiments with an arable, sandy loam soil amended with sugarbeet leaf, the short-term (8 weeks) dynamics of numbers of nematodes were measured in untreated soil and in γ-irradiated soil inoculated with either a field population of soil microorganisms and nematodes or a mixed population of laboratory-propagated bacterivorous nematode species. Sugarbeet leaf stimulated an increase in bacterivorous Rhabditidae, Cephalobidae, and a lab-cultivated Panagrolaimus sp. Differences were observed between the growth rates of the nematode population in untreated and γ-irradiated soils, which were caused by two nematophagous fungi, Arthrobotrys oligospora and Dactylaria sp. These fungi lowered the increase in nematode numbers due to the organic enrichment in the untreated soil. We estimated the annually produced bacterivous nematodes to consume 50 kg carbon and 10 kg nitrogen per ha, per year, in the upper, plowed 25 cm of arable soil.     

Influence of Temperature and Host Plant on the Interaction Between Pratylenchus neglectus and Meloidogyne chitwoodi

The interaction between Pratylenchus neglectus (Pn) and Meloidogyne chitwoodi (Mc) was investigated at soil temperatures of 15, 20, and 25 C on barley and potato. Maximum numbers of Pn and Mc penetrated barley roots at 20 C, whereas a minimum number penetrated at 15 C. Pratylenchus neglectus restricted root penetration by Mc over time and vice-versa. Population densities of each species increased with increasing temperature. Concomitant inoculation of the two species resulted in lower numbers of Pn at 15 and 25 C in both barley and potato, whereas the numbers of Mc were lower at 15 C in barley and at 25 C in potato. Root weights of potato and barley at 15 and 20 C, respectively, were lowered by the presence of both nematodes singly or concomitantly. At 25 C, barley plants inoculated with Mc alone had lower shoot weight than uninoculated controls, but the damage was restricted when Pn also was present. The two species interact competitively, and the outcome varies with soil temperature and host plant. Pn has the potential to suppress Mc population levels and reduce the damage it causes to potato and barley.     

Com Yield Increases Relative to Nonfumigant Chemical Control of Nematodes

Corn yields were measured after application of nematicides in 16 experiments, mostly in medium-to-heavily textured soil, at 12 locations in Iowa during 1973-1976. The average maximum yield increase in plots treated with nematicides was 21% over yields in untreated plots. Yields were correlated negatively with nematode numbers or nematode biomass in nearly all comparisons. Correlations of nematode numbers in the soil with yield averaged -0.56 for Helicotylenchus pseudorobustus, -0.45 for Hoplolaimus galeatus, -0.51 for Pratylenchus spp., and -0.64 for Xiphinema americanum. Correlation coefficients for numbers of nematodes in the roots and yield averaged -0.63 for Pratylenchus spp. and -0.56 H. galeatus. Correlation coefficients for yield and total number of nematodes averaged -0.65 in roots and -0.55 in soils. Negative correlations also were greater for comparisons of yield with total parasitic-nematode biomass than with numbers of individual nematodes of a species or total numbers of parasitic nematodes.     

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.     

Temporal Efficacy of Selected Nematicides on Meloidogyne Species on Tobacco

Aldicarb, ethoprop, and fenamiphos were evaluated for their efficacy in controlling various species of root-knot nematodes on flue-cured tobacco and for their residual activity, as determined through periodic sampling and bioassays of soil taken from field plots. Field experiments were conducted at five locations over 2 years with flue-cured tobacco. Soil in plots treated with nematicides were formed into high, wide beds before transplanting with ''Coker 371-Gold'' or ''K 326'' tobacco. Residual control of Meloidogyne spp. was greatest (P ≤ 0.05) with fenamiphos (in some cases up to 10 weeks, as measured in tomato bioassays of infested soil and root fragments). Suppression of nematode reproduction by ethoprop was short-lived, and numbers of second-stage juveniles + eggs and numbers of galls in bioassays sometimes surpassed those of untreated plots within 4 weeks after treatment. Aldicarb gave intermediate control over time as compared to the other compounds. Although nematicidal efficacy of all compounds varied with site and season, fenamiphos and aldicarb generally produced the highest yields.     

Effects and Dynamics of a Nematode Community on Maize

Relationships between nematode density and yield and between final and preplant population levels were examined in small maize plots on sandy soils in north-central Florida. Plant-parasitic nematodes present in the community included Belonolaimus longicaudatus, Criconemella sphaerocephala, Meloidogyne incognita, Paratrichodorus minor, Pratylenchus brachyurus, and a Xiphinema sp. Plant growth--including stand count, grain yield, stalk weight, and size of young plants--often was inversely correlated (P ≤ 0.05) with densities of B. longicaudatus and occasionally with P. brachyurus, but not with densities of other species or with a range of soil variables. More severe losses in grain yields from B. longicaudatus occurred in 1987 than in 1988, although mean preplant nematode densities in February were similar in both years (4.4 vs. 3.9/100 cm³ soil). Final population densities of most nematode species were linearly related (P ≤ 0.05) to densities measured at planting or earlier. These relationships were stronger (higher r²) with the ectoparasites B. longicaudatus and C. sphaerocephala than with the endoparasites M. incognita and P. brachyurus. No significant correlations were found between population densities of different nematode species.     

Winter Survival of Pratylenchus scribneri

Population densities of Pratylenchus scribneri in a Plainfield loamy sand soil were sampled from 1 October to 1 May for 4 years. From May to October of each year, the site was planted to Russet Burbank potato and Wis 4763 corn. Percentages of change in population densities of nematodes were computed on the basis of number of nematodes present on 1 October. The decline of P. scribneri between growing seasons was nonlinear, with most mortality occurring in the autumn before the soil froze. Winter survival, defined as the percentage of change in population densities from 1 October to 1 May the following year, ranged from 50 to 136% for nematodes in corn plots and from 15 to 86% for nematodes in potato plots. There was no difference in survival of nematodes of different life stages or among root and soil habitats. Winter survival of nematodes was density-dependent in 3 of 4 years in corn plots and in 1 of 4 years in potato plots. Although predators were present, their abundance was not correlated with the winter survival of nematodes. Cumulative and average snow cover was correlated with the survival of nematodes associated with corn but not with potato. No relationships between other climatic factors and survivorship were detected.     

Abundance and Vertical Distribution of Longidorus breviannulatus Associated with Corn and Potato

Longidorus breviannulatus was detected in a field planted to corn after 13 years of potato. Nematode populations were maintained in this field in adjacent corn and potato plots for 2 years but did not increase significantly on either crop. Population levels increased until approximately 60 days after planting and then declined until the end of the growing season. Overwinter mortality was negligible. The vertical distribution of the nematode population changed during the course of the season. More nematodes were recovered from depths of 0-15 cm in early season samples and from depths of 15-30 cm in late season samples. Data indicated that this redistribution was due to nematode migration.     

Parasitism of Nematodes by the Fungus Hirsutella rhossiliensis as Affected by Certain Organic Amendments

Experiments were conducted to determine whether the addition of organic matter to soil increased numbers of bacterivorous nematodes and parasitic activity of the nematophagous fungus Hirsutella rhossiliensis. In a peach orchard on loamy sand, parasitism of the plant-parasitic nematode Criconemella xenoplax by H. rhossiliensis was slightly suppressed and numbers of C. xenoplax were not affected by addition of 73 metric tons of composted chicken manure/ha. In the laboratory, numbers of bacterivorous nematodes (especially Acrobeloides spp.) and fungivorous nematodes increased but parasitism of nematodes by H. rhossiliensis usually decreased with addition of wheat straw or composted cow manure to a loamy sand naturally infested with H. rhossiliensis. These results do not support the hypothesis that organic amendments will enhance parasitism of nematodes by H. rhossiliensis.     

Effects of midas® on nematodes in commercial floriculture production in Florida

Cut flower producers currently have limited options for nematode control. Four field trials were conducted in 2006 and 2007 to evaluate Midas® (iodomethane:chloropicrin 50:50) for control of root-knot nematodes (Meloidogyne arenaria) on Celosia argentea var. cristata in a commercial floriculture production field in southeastern Florida. Midas (224 kg/ha) was compared to methyl bromide:chloropicrin (98:2, 224 kg/ha), and an untreated control. Treatments were evaluated for effects on Meloidogyne arenaria J2 and free-living nematodes in soil through each season, and roots at the end of each season. Plant growth and root disease were also assessed. Population levels of nematodes isolated from soil were highly variable in all trials early in the season, and generally rebounded by harvest, sometimes to higher levels in fumigant treatments than in the untreated control. Although population levels of nematodes in soil were not significantly reduced during the growing season, nematodes in roots and galling at the end of the season were consistently reduced with both methyl bromide and Midas compared to the untreated control. Symptoms of phytotoxicity were observed in Midas treatments during the first year and were attributed to Fe toxicity. Fertilization was adjusted during the second year to investigate potential fumigant/fertilizer interactions. Interactions occurred at the end of the fourth trial between methyl bromide and fertilizers with respect to root-knot nematode J2 isolated from roots and galling. Fewer J2 were isolated from roots treated with a higher level of Fe (3.05%) in the form of Fe sucrate, and galling was reduced in methyl bromide treated plots treated with this fertilizer compared to Fe EDTA. Reduced galling was also seen with Midas in Fe sucrate fertilized plots compared to Fe EDTA. This research demonstrates the difficulty of reducing high root-knot nematode population levels in soil in subtropical conditions in production fields that have been repeatedly fumigated. Although soil population density may remain stable, root population density and disease can be reduced.     

Effects of Potato-Cotton Cropping Systems and Nematicides on Plant-Parasitic Nematodes and Crop Yields

Belonolaimus longicaudatus has been reported as damaging both potato (Solanum tuberosum) and cotton (Gossypium hirsutum). These crops are not normally grown in cropping systems together in areas where the soil is infested with B. longicaudatus. During the 1990s cotton was grown in a potato production region that was a suitable habitat for B. longicaudatus. It was not known how integrating the production of these two crops by rotation or double-cropping would affect the population densities of B. longicaudatus, other plant-parasitic nematodes common in the region, or crop yields. A 3-year field study evaluated the viability of both crops in monocropping, rotation, and double-cropping systems. Viability was evaluated using effects on population densities of plant-parasitic nematodes and yields. Rotation of cotton with potato was found to decrease population densities of B. longicaudatus and Meloidogyne incognita in comparison with continuous potato. Population densities of B. longicaudatus following double-cropping were greater than following continuous cotton. Yields of both potato and cotton in rotation were equivalent to either crop in monocropping. Yields of both crops were lower following double-cropping when nematicides were not used.     

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.     

Response of Resistant and Susceptible Bell Pepper (Capsicum annuum) to a Southern California Meloidogyne incognita Population from a Commercial Bell Pepper Field

To determine the presence and level of root-knot nematode (Meloidogyne spp.) infestation in Southern California bell pepper (Capsicum annuum) fields, soil and root samples were collected in April and May 2012 and analyzed for the presence of root-knot nematodes. The earlier samples were virtually free of root-knot nematodes, but the later samples all contained, sometimes very high numbers, of root-knot nematodes. Nematodes were all identified as M. incognita. A nematode population from one of these fields was multiplied in a greenhouse and used as inoculum for two repeated pot experiments with three susceptible and two resistant bell pepper varieties. Fruit yields of the resistant peppers were not affected by the nematodes, whereas yields of two of the three susceptible pepper cultivars decreased as a result of nematode inoculation. Nematode-induced root galling and nematode multiplication was low but different between the two resistant cultivars. Root galling and nematode reproduction was much higher on the three susceptible cultivars. One of these susceptible cultivars exhibited tolerance, as yields were not affected by the nematodes, but nematode multiplication was high. It is concluded that M. incognita is common in Southern California bell pepper production, and that resistant cultivars may provide a useful tool in a nonchemical management strategy.     

Effect of Criconemella onoensis on Potato

Criconemella onoensis (Luc) Luc and Raski increased to high (458-1,290/100 cm³) soil population densities in four fields planted to cover crops of sorghum-sudangrass (Sorghum bicolor (L.) Moench × S. arundinaceum (Desv.) Stapf var. sudanense (Stapf) Hitchc. ''Funk FP-4'') during the summer of 1984 in southeastern Florida. Three pathogenicity tests conducted in the greenhouse with C. onoensis on potato (Solanum tuberosum L. ''La Rouge'') using three different methods (inoculation, chemical treatment of infested soil, or pasteurization of infested soil) revealed no significant (P = 0.10) differences in plant growth, despite significant (P = 0.05) differences in population densities of C. onoensis between treated and control pots in each test. In these three tests, the maximum initial density of C. onoensis used was 720/100 cm³ soil and the maximum final density was 686/100 cm³ soil. Application of 933 liters/ha of Vapam to a field site with a pretreatment density of 1,120 C. onoensis/100 cm³ soil significantly (P = 0.05) reduced populations compared with untreated control plots, but yields remained higher in control plots. Apparently C. onoensis has no significant effect on potato growth at the population densities tested.