Decline of Globodera rostochiensis as Influenced by Potato Root Diffusate Movement and Persistence in Soil

Decline of Globodera rostochiensis populations occurring naturally in soil and those added to potato hills and furrow centers in nylon bags was correlated with root weight of Hudson, Rosa, and Katahdin potatoes at two locations in New York. Cysts in bags were added to soil at planting and at 1, 3, 5, 7, and 9 weeks after emergence (AE). Fallow decline required only 2-4 weeks in soil and did not increase with time. Decline due to growing potatoes was greater in hills than in furrow centers, and resistant Hudson potatoes stimulated greater nematode hatch for longer times in both hills and furrows than did resistant Rosa and susceptible Katahdin. Potato root diffusate (PRD) was produced in highest concentration early in the season; decreased egg hatch with time was probably the result of declining PRD production and inactivation of PRD in soil. Decreasing potato row spacing from 92 cm to 46 and 23 cm between rows increased G. rostochiensis decline in furrow centers, with the majority of decline occurring within 1-3 weeks AE. Replanting potatoes after 1 week of trap crop growth failed to favor population reduction over a single full season crop.     

Survival of Heterodera zeae in Soil in the Field and in the Laboratory

Eggs and (or) second-stage juveniles (J2) inside cysts of Heterodera zeae survived over winter in the field with no detectable mortality at all six depths to 30 cm from which soil samples were collected between corn stubble in the row at 4-8-week intervals. Few or no free J2 were recovered from soil collected in January-April from the top 5 cm, but some were recovered at all samplings from soil collected at greater depths. Emergence of J2 from cysts and numbers of females developing on corn roots in bioassays of cysts increased substantially between January and April. Cyst numbers in a fallow area of the corn field did not decline at any depth to 30 cm during 20 months. Free soil J2, J2 emerged from cysts, and females from the bioassay of cysts were highest at the first soil sampling in July after 10 months of fallow; numbers of nematodes in all three categories declined thereafter, but a few were still detectable after 20 months of fallow. Some cysts were still being recovered after 51 months from naturally infested field soil stored moist in the laboratory at 2 C and 24 C. Females were produced in the bioassays of cysts recovered from soil stored for 38 months at 24 C and for 32 months at 2 C. No free J2 were recovered from soil after 1 month of storage at -18 C, but even after 7 months storage J2 emerged from cysts that were recovered and many females developed in bioassays of those cysts.     

太阳能消毒对温室土壤环境效应及防治黄瓜根结线虫病效果

采用室内测定与大田试验相结合的方法,研究了太阳能不同消毒方式对温室土壤环境的效应及对温室黄瓜根结线虫病的控制效果.结果表明,垄沟式覆盖地膜处理对温室土壤温度、土壤酶的活性、微生物数量的影响最明显,处理16d,棚室10、20、30、40、50cm深土壤的最高温度依次是59.1、57.7、56.6、48.9、47.6℃,平均每天超过55、50、45℃持续时间分别为7.5、8.5h和16h;土壤温度的升高,有利于提高对根结线虫的杀灭效果.0～20cm土壤脲酶、蔗糖酶、碱性磷酸酶、过氧化氢酶分别降低43.3%、18.7%、20.1%和13.1%;土壤真菌、细菌、放线菌数量分别降低96.0%、84.8%、53.9%.垄沟式未覆膜处理对土壤环境的影响次之,平面式未覆膜的影响最小,酶活性降低及土壤微生物数量下降对土壤的活性有一定的负效应.垄沟式覆膜太阳能消毒对温室黄瓜根结线虫控制效果最显著,持效期最长,能有效杀灭温室0～50cm土壤内根结线虫;处理后第1年和第2年对温室黄瓜根结线虫控制效果均达到100%,第3年防效96.7%,第5年仍达72.8%.垄沟式未覆膜控制效果次之;平面式未覆膜控制效果最差,持效期最短.     

Nematode Community Structure in a Vineyard Soil

Distribution of the nematode community in a California vineyard was studied over a 13-month period. Omnivorous and microbivorous nematodes were similarly distributed in the root zone, with greatest densities occurring between vine rows and near the soil surface. Greatest densities of plant-parasitic nematodes were found in the vine row, with the individual species differing in their vertical distribution. Total nematode biomass was greatest between rows near the surface. Biomass of plant parasites was greatest in the upper 30 cm of soil in the row, whereas biomass of microbivores was greatest in this region between rows. Of the plant-parasitic nematodes, the variability in distribution among vines was greatest for Paratylenchus hamatus and least for Meloidogyne spp.     

Survival and Infectivity of Bursaphelenchus xylophilus in Wood Chip-Soil Mixtures

To determine the effect of soil environment on the life stages and total numbers of Bursaphelenchus xylophilus, nematode-infested wood chips alone and mixed with soil were incubated at 12 and 20 C. Nematodes were extracted at 2-week intervals for 12 weeks. Numbers of nematodes and percentage of third-stage dispersal larvae were greater at 12 C and in chips without soil. Percentage of juveniles of the propagative cycle was greater at 20 C and in chips with soil. Although B. xylophilus survived in chips with soil for 12 weeks, nematode numbers and life stage percentages changed little over time. To determine if B. xylophilus was capable of infecting wounded roots, infested and uninfested chips were mixed with soil in pots with white and Scots pine seedlings. Trees were maintained at 20 and 30 C and harvested at mortality or after 12 weeks. Only seedlings treated with infested chips contained nematodes. In field experiments, planted seedlings were mulched with infested chips to determine if nematodes would invade basal stem wounds. Among these trees, Scots pine was more susceptible than white or red pines to infection and mortality.     

Interactions between Nematodes and Earthworms: Enhanced Dispersal of Steinernema carpocapsae

Dispersal of the nematode Steinernema carpocapsae (All strain), applied on the top or the bottom of soil columns, was tested in the presence or absence of two earthworm species, Lumbricus terrestris or Aporrectodea trapezoides. Nematode dispersal was estimated after a 2-week period with a bioassay against the greater wax moth, Galleria mellonella. Vertical dispersal of nematodes was increased in the presence of earthworms. When nematodes were placed on the surface of soil columns, significantly more nematodes dispersed to the lower half of the columns when either earthworm species was present than when earthworms were not present. When nematodes were placed on the bottom of soil columns, significantly more nematodes dispersed to the upper half of the columns when L. terrestris was present than when A. trapezoides was present or in the absence of earthworms. Because nematodes were found on the exterior and in the interior of earthworms, nematode dispersal may be enhanced by direct contact with the earthworms.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana carpocapsae (Nematoda: Steinernematidae)

The vertical migration of N. carpocapsae infective juveniles applied to the soil surface or introduced 14 cm below the soil surface was studied in four different soil types (pure silica sand, coarse sandy loam, silty clay loam, and clay). The percentage of juveniles able to migrate and infect wax moth pupae placed in the soil decreased as the percentage of clay and silt increased. Most nematodes placed on the soil surface remained within 2 cm of the surface, but some penetrated to a depth of 10 cm in pure silica sand and coarse sandy loam to infect pupae. Some pupae at the same depth were also infected with nematodes in silty clay loam soil. In pure silica sand and coarse sandy loam, nematodes introduced 14 cm below the soil surface were able to infect wax moth pupae located between 4 and 24 cm. Movement was least in clay soil and limited in silty clay loam. Nematodes showed a tendency to disperse upwards from the point of application. In all cases the number of migrating nematodes was greatest when wax moth pupae were present.     

Effect of Soil Texture on the Distribution and Infectivity of Neoaplectana glaseri (Nematoda: Steinernematidae)

The vertical migration of infective juveniles of Neoaplectana glaseri applied to the soil surface or introduced 16 cm below the soil surface was studied in pure silica sand, coarse sandy loam, silty clay loam, and clay. The number of juveniles that migrated and infected wax moth pupae placed in the soil decreased as the proportion of clay and silt increased. The majority of nematodes moved downwards 2-6 cm from the surface, but some penetrated to a depth of 14 cm in pure silica sand and coarse sandy loam. In pure silica sand and coarse sandy loam, nematodes introduced 16 cm below the soil surface were able to infect wax moth pupae located at depths of 0-4 cm and 28-32 cm. Nematodes showed a greater tendency to disperse downwards from the point of application. Movement of the nematode was least in clay soil and limited in silty clay loam soil. The number of migrating nematodes was greatest when wax moth pupae were present.     

Steinernema feltiae (DD-136) and S. glaseri: Persistence in Soil and Bark Compost and Their Influence on Native Nematodes

Infective juveniles (J3) of the entomogenous nematodes Steinernema feltiae DD-136 (ca. 10,000 J3/100 ml) and S. glaseri (ca. 2,500 J3/100 ml) were incubated in steam-sterilized and nonsterilized sandy soil and bark compost for 8 weeks at 25 C. The nematodes were recovered by a two-step extraction procedure at 1-week intervals, and their infectivity to lepidopterous larvae (Spodoptera litura and Galleria mellonella) and their effect on the population and community of native nematodes in soil were determined. Survival of inoculated nematodes and mortality of insects were enhanced in sterilized media. Nonsterilized bark compost proved to be equally as suitable a medium as sterilized compost. In nonsterilized soil, the survival curve of S.feltiae declined more rapidly than that or S. glaseri which was less infective to insects despite its greater persistence even in nonsterilized soil. Soon after the addition of steinernematids to soil, the population of native nematodes showed a fluctuation with an increase in rhabditids and a decrease in other kinds of nematodes.     

Persistence of Heterorhabditis Infective Juveniles in Soil: Comparison of Extraction and Infectivity Measurements

The persistence of Heterorhabditis megidis in soil was studied over a 4-week period. On days 0, 2, 14, and 28, infective juveniles (IJ) were extracted by centrifugal flotation, Baermann funnel, and baiting of soil with Tenebrio molitor larvae, which were then dissected. Extraction efficiencies on day 0 were 82% by centrifugal flotation, 56% by Baermann funnel, and 19.8% by bait insect. The relative efficiency of the three methods changed over time. The relationship between the density of nematodes in the soil and the proportion recovered by dissection was non-linear. Up to a dose of approximately 60 IJ/insect, less than 12% became established, while at higher doses (up to 200 IJ/insect) the invasion efficiency was 23%. Mortality of bait insects increased from day 0 to day 2, but decreased to day 28. A novel method of assessing soil pathogenicity by preparing a soil density series and calculating the dose of soil or IJ that kills 50% of the bait insects gave a similar pattern. This method is recommended as a means of tracking changes in pathogenicity over time when bait insect mortality in undiluted soil is at or near 100%. Two methods of preparing a series of Heterorhabditis IJ densities in soil, either by diluting the soil itself with IJ-free soil or by adding diluted suspensions of IJ to the soil, resulted in the same bait insect mortalities.     

Effects of Seasonal and Site Factors on Xiphinema index Populations in Two California Vineyards

Sampling of Xiphinema index for 2 years (1993-95) in two California vineyards indicated that a greater number of nematodes occurred during the winter months. The number of juveniles increased four-fold from December 1993 to January 1994, indicating a high reproductive rate during this time. Extremely high or low soil temperatures corresponded to low nematode numbers. Samples were taken from 0 to 31 cm and 31 to 62 cm deep both within and between the vine rows. Numbers of nematodes were greatest at the 0- to 31-cm depth in one vineyard with a loamy sand soil, and at a depth of 31 to 62 cm in the second vineyard, which had a silt loam soil. In both vineyards, X. index population densities were greater within the vine row.     

Spatial and temporal distribution of endemic entomopathogenic nematodes in a heterogeneous vegetable production landscape

Entomopathogenic nematodes within the families Steinernematidae and Heterorhabditidae (Order: Rhabditida) are potential biological control agents for many soil-dwelling vegetable pests. However, their low persistence and efficacy after field releases have resulted in limited use in pest management programs. Understanding the factors regulating natural populations of entomopathogenic nematodes may provide insight into practices to conserve populations within production systems. A series of investigations were conducted within a vegetable production area in Willard, Ohio during 2000–2003 to gain insight into the population ecology of endemic populations of entomopathogenic nematodes. A total of 440 sites across four habitats associated with the production landscape were sampled to ascertain the natural occurrence of these beneficial nematodes. Habitats included cultivated areas, grassy banks adjacent to cultivated areas, undisturbed shrub lands and forests. Twelve sites along grassy banks were monitored over a growing season to estimate associations between abiotic and biotic factors and endemic populations. Entomopathogenic nematodes were only detected along grassy banks adjacent to the cultivated areas; nematodes were recovered from 15 to 30% of sites sampled in 2001 and 2002, respectively. Two species of nematodes were isolated, Heterorhabditis bacteriophora Poinar and Steinernema feltiae Filipjev. H. bacteriophora was the most prevalent nematode species and was recovered from 60% of positive samples. Nematode populations varied temporally and spatially along grassy banks; mean population density over the growing period was 1313 infective juveniles/m². Neither macro- nor microarthropod communities nor soil temperature differed between sites at which nematodes were detected and those at which nematodes were not detected. Soil moisture, however, was associated with the occurrence and persistence of nematodes along grassy banks; mean soil moisture at sites at which nematodes were detected and those sites at which nematodes were not detected was 37.3 and 26.8%, respectively. Water management is an important component of vegetable production and our results suggest that soil moisture manipulation would be important in the establishment and sustained presence of entomopathogenic nematode populations within cultivated areas over the growing season.     

Dispersal and Infectivity of the Entomogenous Nematode,Neoaplectana carpocapsae Weiser (Rhabditida: Steinernematidae), in Sand

Laboratory tests determined the lateral and vertical dispersal patterns of Neoaplectana carpocapsae in sand. In the vertical tests, placement of infective juveniles 15 cm below the sand''s surface resulted in the majority (77%) being recovered above the point of placement after 48 h. Placement of the nematodes on the sand''s surface resulted in the majority (90.4%) remaining within 1 cm of the sand''s surface. Placement of nematodes at depths of 2.5 cm and 5.0 cm below the sand''s surface also resulted in little nematode dispersal. However, vertical hioassay tests showed that juvenile nematodes placed on the sand''s surface dispersed 12 cm down to infect 67% of the Galleria mellonella pupae placed at the depth. Conversely, when nematodes were placed 11 cm below the insect pupae no infection was observed, but 53% infection occurred when nematodes were 7 cm below the site of the insect pupae. In lateral dispersal, 87% of the nematodes rentained within 2 cm of the placement site, although 0.5% were recovered at 12-14 cm away from the point of placement. Lateral bioassay tests indicated that the nematodes were capable of infecting 90, 35, and 5% of the G. mellonella pupae at 7 cm, 10 cm, and 14 cm from the point of placement, respectively.     

Spatial Patterns of Entomopathogenic Nematodes in Microcosms: Implications for Laboratory Experiments

Laboratory microcosms were used to: i) measure the effects of soil moisture on survival of Steinernema riobravis and ii) investigate the suitability of using microcosms to study motility and survival of these nematodes. Nematodes recovered from soil contained in petri dishes declined by more than 95% during 7 days, whereas nematodes recovered from the inner surfaces of dishes increased 35-fold. After 7 days in dishes, >20 times as many nematodes were recovered from dish surfaces than from soil. Nematodes exhibited a negative geotropism; greater numbers of nematodes were recovered from the lid surfaces than from the surfaces of dishes. Survivorship of nematodes in soil in plastic centrifuge tubes was somewhat greater than in petri dishes, and fewer nematodes ascended above the soil line in tubes than dishes. Downward migration of nematodes was inversely related to soil column diameter, possibly due to relatively unimpeded movement along container surfaces. An assay was developed by which nematodes were rinsed from the inner surfaces of centrifuge tubes into the soil. The resulting slurry was then processed on Baermann trays to recover motile nematodes. Nematode survival in soil in centrifuge tubes was higher at soil moistures between 2-4% than at lower (0.5-1.0%) and higher (4.0-12.0%) moisture levels. Survival of S. riobravis may be enhanced by quiescence induced by moisture deficits.     

Movement of entomopathogenic nematodes in soils of Fragaria spp

The mobility of three entomopathogenic nematodes (Steinernema carpocapsae UK and All Strain, and S. glaseri (Nematoda: Steinernematidae) was observed in strawberry fields in Vancouver, WA. Nematodes were sprinkled over the soil surface using a mason jar. Soil and soil-moisture content, soil composition, soil pH and conductivity was reported over the evaluation period. 12 cm deep soil samples were taken after surface application at 9 and 25 days, 7, 26 and 45 and 6, 22, 37 and 50 days at the three different test sites within the surface application site and at 5 cm distance. Soil samples taken were divided into three layers (0-4, 5-8 and 9-12 cm) and exposed once to five Galleria larvae in the laboratory to evaluate nematode presence and movement. Results after surface application demonstrated more vertical movement of S. glaseri into deeper soil layers in comparison to both S. carpocapsae strains.     

Use of Nematodes as Biomonitors of Nonfumigant Nematicide Movement through Field Soil

Three field experiments were established in a loamy sand soil in the Coastal Plain of North Carolina to determine downward movement of aldicarb and fenamiphos with a nematode bioassay. Penetration of bioassay plant roots by Meloidogyne incognita was measured at 1, 3, 7, 14, 21, and 28 days after treatment in the greenhouse as a means of determining nematicide effectiveness. Chemical movement was similar in planted and fallow soil. Nematicidal activity was greater in soil collected from the 0 to 10 cm depth than from the 10 to 20 cm depth. Fenamiphos suppressed host penetration by the nematode more than aldicarb under the high rainfall (19 cm) and low soil temperatures that occurred soon after application in the spring. During the summer, which had 13 cm precipitation and warmer soil temperatures, both chemicals performed equally well at the 0 to 10 cm depth. At the lower soil level (10 to 20 cm), aldicarb limited nematode penetration of host roots more quickly than fenamiphos. Both of these chemicals moved readily in the sandy soil in concentrations sufficient to control M. incognita. Although some variability was encountered in similar experiments, nematodes such as M. incognita have considerable potential as biomonitors of nematicide movement in soil.     

Nematode Response to Carbofuran

Higher populations of Meloidogyne incognita larvae and Pratylenchus penetrans were recovered from soil treated with carbofuran 10 and 15 days after treatment, respectively, than were recovered from untreated control soil. The number of P. penetrans, however, was lower 50 days after treatment, and symptoms developed only occasionally on the root systems of host plants. Populations of Tylenchorhynchus claytoni inoculated at different distances from the base of corn seedlings growing in carbofuran-treated soil did not move toward the plant, whereas they were attracted in untreated soil from a distance of 12 cm. P. penetrans moved at random in treated agar medium when inoculations occurred 4 cm away from the root tips of tomato seedlings under aseptic conditions. Those nematodes that reached the roots were never observed feeding during a 20-day observation period. Specimens of P. penetrans placed on the developing roots moved at random and never penetrated. In contrast, numerous P. penetrans penetrated roots of seedlings growing in untreated medium.     

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.     

Effect of Compost and Manure Soil Amendments on Nematodes and on Yields of Potato and Barley: A 7-Year Study

A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.     

Escape of Steinernema feltiae from Alginate Capsules Containing Tomato Seeds

The entomogenous nematode Steinernema feltiae was encapsulated in an alginate matrix containing a tomato seed. When these capsules were placed on 0.8% agar for 7 days, the seed germinated and ca. 20% of the nematodes escaped from the capsules, whereas only 0.1% escaped from capsules without seeds. When capsules containing nematodes and a seed were planted into sterilized or nonsterilized soil, nematodes escaped to infect Galleria mellonella larvae. When seed in capsules containing ca. 274 nematodes per capsule were planted in nonsterilized soil, Galleria mortality was 90% 1 week later. Galleria mortality declined to 27%, 23%, and 0% in weeks 2, 4, and 8 postplant, respectively. In sterilized soil, Galleria mortality was 96% and did not differ significantly from the nonsterilized soil in week 1, but was significantly higher in sterilized soil over nonsterilized soil for week 2 (81%) and week 4 (51%). When capsules containing nematodes only were used, Galleria mortality was 71% in sterilized soil 1 week after planting and 58%, 33%, and 12% in weeks 2, 4, and 8 postplant, respectively. In nonsterilized soil, Galleria mortality was 8%, 30%, 21%, and 28% after 1, 2, 4, and 8 weeks, respectively, using only encapsulated nematodes. When the number of nematodes per capsule was increased to ca. 817, Galleria mortality was 92 % or higher in sterilized soil from week 1 to week 4.