Plant-parasitic Nematode Acetylcholinesterase Inhibition by Carbamate and Organophosphate Nematicides

The sensitivity of acetylcholinesterases (ACHE) isolated from the plant-parasitic nematodes Meloidogyne arenaria, M. incognita, and Heterodera glycines and the free-living nematode Caenorhabditis elegans to carbamate and organophosphate nematicides was examined. The AChE from plant-parasitic nematode species were more sensitive to carbamate inhibitors than was AChE from C. elegans, but response to the organophosphates was approximately equivalent. The sulfur-containing phosphate nematicides were poor inhibitors of nematode acetylcholinesterase, but treatment with an oxidizing agent greatly improved inhibition. Behavioral bioassays with living nematodes revealed a poor relationship between enzyme inhibition and expression of symptoms in live nematodes.     

Endoparasitic Nematodes in Maize Roots in the Western Transvaal as Related to Soil Texture and Rainfall

Eight endoparasitic nematode species were recovered from 170 maize root samples in western Transvaal, Republic of South Africa. Pratylenchus zeae had the highest average population density (17,454/5 g roots), followed by P. neglectus (5,827/5 g roots), P. penetrans (5,617/5 g roots), P. brachyurus (3,060/5 g roots), Meloidogyne incognita plus M. javanica (301 juveniles/5 g roots), P. crenatus (130/5 g roots), and Rotylenchutus parvus (64/5 g roots). The 17 reasonably homogeneous farming areas (RHFA) surveyed could be ranked on the basis of the incidence of the prevalent nematode species. A positive relationship was found between the incidence of P. brachyurus and R. parvus and long-term average annual rainfall. The incidence of P. penetrans and the Meloidogyne spp. was positively related to a combination of sand percentage and long-term average annual rainfall.     

Nematicides and Nonconventional Soil Amendments in the Management of Root-Knot Nematode on Cotton

Granular and liquid commercial humates, with micronutrients, and a microbial fermentation product were compared in several combinations with nematicides for their effects on cotton lint yield and root-knot nematode suppression. Fumigant nematicides effectively reduced cotton root galling caused by root-knot nematodes, and cotton lint yields increased. Organophosphates and carbamates were not effective. Occasionally, cotton lint yields were increased or maintained with combination treatments o f humates, micronutrients, and a microbial fermentation product, but galling o f cotton roots by root-knot nematodes was usually not reduced by these treatments.     

Distribution of Field Corn Roots and Parasitic Nematodes in Subsoiled and Nonsubsoiled Soil

A field trial was conducted for 2 years in an Arredondo fine sand containing a tillage pan at 15-20 cm deep to determine the influence of subsoiling on the distribution of corn roots and plant-parasitic nematodes. Soil samples were taken at various depths and row positions at 30, 60, and 90 days after planting in field corn subsoiled under the row with two chisels and in non-subsoiled corn. At 30 and 60 days, in-row nematode population densities to 60 cm deep were not affected by subsoiling compared with population densities in nonsubsoiled plots. After 90 days, subsoiling had not affected total root length or root weight at the 20 depth-row position sampling combinations, but population densities of Meloidogyne incognita and Criconemella spp. had increased in subsoiled corn. Numbers of Pratylenchus zeae were not affected. Subsoiling generally resulted in a change in distribution of corn roots and nematodes in the soil profile but caused little total increase in either roots or numbers of nematodes. Corn yield was increased by subsoiling.     

Applying Nematicides through an Overhead Sprinkler Irrigation System for Control of Nematodes

Phenamiphos, ethoprop, and carbofuran each at 6.7 kg a.i./ha were applied to squash, southern pea, and corn via injection into a sprinkler irrigation system. This method was then compared with a conventional application of phenamiphos and ethoprop granules spread on the soil surface and incorporated into the top 15 cm for control of Macroposthonia ornata and Meloidogyne incognita. Nematode populations in the soil and root-gall indices were lower, and yields greater, in treated than in untreated plots, but there were no significant differences between the methods of application in most comparisons.     

Influence of Temperature on Population Development of Eight Species of Pratylenchus on Soybean

In a soil temperature study, population increase on ''Clark 63'' soybeatt was most rapid at 30 C in Pratylenchus alleni, P. brachyurus, P. cofleae, P. neglectus, P. scribneri, and P. zeae and at 25 C in P. penetrans and P. vulnus. The last two were the only species that reproduced at 15 C. Populations of all species increased over the range of 20-30 C, except those of P. neglectus at 20 C and P. coffeae, which was not tested below 25 C. Only P. brachyurus, P. neglectus, P. scribneri and P. zeae reproduced at 35 C. At their optimum temperatures, P. scribneri exhibited the greatest population increase, 1248-fold, and P. penetrans the least, 32-fold. This is the first report of soybean as a host for P. vulnus.     

Species of Pratylenchus Associated with Solanum tuberosum cv Superior in Ohio

Seventy-three Ohio fields comprising ca. 440 ha of cv Superior potatoes were surveyed in 1977 for plant-parasitic nematodes. Of eight genera of plant-parasitic nematodes, Pratylenchus was found most frequently, occurring in 65% of the soil samples and 84% of the root samples. Populations of Pratylenchus were consistently higher than populations of the other nematode genera. The six species of Pratylenchus extracted from potato roots, in descending order of frequency, were P. crenatus, P. penetrans, P. scribneri, P. alleni, P. thornei, and P. neglectus. Prevalence of these Pratylenchus species in Ohio potato fields suggests that they could be involved with vascular wilt fungi in premature death of cv Superior potato vines known in Ohio as "early dying."     

Effects of One and Two Applications of Nematicides on Nematode Populations and Soybean Yields

Yields of ''McNair 800'' soybeans, Glycine max (L.) Merr., were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied at-planting and with phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Meloidogyne incognita (Kofoid and White) Chitwood. Yields of ''GaSoy 17'' were significantly increased with ethylene dibromide + chloropicrin, DBCP, phenamiphos, and aldicarb applied, preplant and with DBCP, carbofuran, phenamiphos, aldicarb, and DBCP applied postplant to soil infested with Hoplolaimus columbus Sher. In several instances, preplant or at-planting treatments plus postplant treatments with the same or different chemicals were more effective than either treatment alone. Generally, the fumigants were more effective than the nonfumigants when they were applied at-planting to M. incognita-infested soil and preplant to H. columbus-infested soil. Phenamiphos, aldicarb, and DBCP were about equally effective when they were applied postplant in M. incognita-infested soil, but DBCP was more effective than carbofuran. Carbofuran, phenamiphos, aldicarb, and DBCP were about equally effective when applied postplant to H. columbus-infested soil.     

Vertical Distribution of Three Namatode Species in Relation to Certain Soil Properties

Population densities of Belonolaimus longicaudatus, Pratylenchus brachyurus, and Trichodorus christiei were determined from soil samples taken weekly in Tifton, Georgia during a 14-month period (except for April and May) at 15-cm increments to a depth of 105 cm. Belonolaimus longicaudatus predominately inhabited the top 30 cm of soil that was 87-88% sand, 6-7% silt, and 5-7% clay. No specimens were found below 60 cm where the soil was 76-79% sand, 5-6% silt, and 15-19% clay. Highest population densities occurred during June through September when temperature in the top 30 cm of soil was 22-25 C and soil moisture was from 9 to 20% by volume. Pratylenchus brachyurus was found at all depths, but population densities were greatest 45-75 cm deep where the soil was 78-79% sand, 6% silt, and 15-16% clay. In the months monitored, highest population densities occurred during March, June, and December when the soil temperature 45-75 cm deep was 14-17 C and soil moisture was 22-42%. Trichodorus christiei was found at all depths, but population densities were highest 30 cm deep where the soil was 83% sand, 5% silt, and 12% clay. Highest population densities occurred during December through March when the soil temperature 30 cm deep was 11-17 C and soil moisture was 18-23%.     

Population Dynamics of Plant Nematodes in Cultivated Soil: Length of Rotation in Newly Cleared and Old Agricultural Land

During a 6-year study of 1-, 2-, and 3-year crop rotations, population densities of Pratylenchus brachyurus, Trichodorus christiei, and Meloidogyne incognita were significantly affected by the choice of crops but not by length of crop rotation. The density of P. brachyurus and T. christiei increased rapidly on milo (Sorghum vulgate). In addition, populations of P. brachyurus increased significantly in cropping systems that involved crotalaria (C. rnucronata), millet (Setaria italica), and sudangrass (Sorghum sudanense). Lowest numbers of P. brachyurus occurred where okra (Hibiscus esculentus) was grown or where land was fallow. The largest increase in populations of T. christiei occurred in cropping systems that involved millet, sudangrass, and okra whereas the smallest increase occurred in cropping systems that involved crotalaria or fallow. A winter cover of rye (Secale cereale) had no distinguishable effect on population densities of P. brachyurus or T. christiei. Meloidogyne incognita was detected during the fourth year in both newly cleared and old agricultural land when okra was included in the cropping system. Detectable populations of M. incognita did not develop in any of the other cropping systems. Yields of tomato transplants were higher on the newly cleared land than on the old land. Highest yields were obtained when crotalaria was included in the cropping system. Lowest yields were obtained when milo, or fallow were included in the cropping system. Length of rotation had no distinguishable effect on yields of tomato transplants.     

Managing Nematode Population Densities on Tomato Transplants Using Crop Rotation and a Nematicide

Millet, milo, soybean, crotalaria, and Norman pigeon pea were used in conjunction with clean fallow and a nematicide (fensulfothion) for managing nematode populations in the production of tomato transplants (Lycopersicon esculentum Mill.). Glean fallow was the most effective treatment in suppressing nematode numbers. After 2 years in tomato, root-knot nematodes increased in numbers to damaging levels, and fallow was no longer effective for complete control even in conjunction with fensulfothion. After 4 years in tomato, none of the crops used as summer cover crops alone or in conjunction with fensulfothion reduced numbers of root-knot nematodes in harvested tomato transplants sufficiently to meet Georgia certification regulations. Milo supported large numbers of Macroposthonia ornata and Pratylenchus spp. and crotalaria supported large numbers of Pratylenchus spp. Millet, milo, soybean, crotalaria, and pigeon pea are poor choices for summer cover crops in sites used to produce tomato transplants, because they support large populations of root-knot and other potentially destructive nematodes.     

Carbamate and Organophosphorus Nematicides: Acetylcholinesterase inhibition and Effects on Dispersal

The sensitivities of acetylcholinesterases (ACHE) from the fungus-feeder Aphelenchus avenae and the plant-parasitic species Helicotylenchus dihystera and Pratylenchus penetrans and the housefly, Musca domestica, were compared using a radiometric assay which utilized H³ acetylcholine as a substrate. Nematode ACHE were generally less sensitive to inhibition by organophosphorns and carbamate pesticides than were ACHE from the housefly. ACHE from the plant-parasitic species and A. avenae were generally similar in sensitivity. In soil, carbamates were more toxic than the organophosphorus pesticides to A. avenae. All pesticides tested affected nematode movement, but fenamiphos was more inhibitory than others. The effects on dispersal of nematodes may be an important mechanism in control by some nematicides.     

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.     

Axenizing and Culturing Endomigratory Plant-Parasitic Nematodes using Pluronic F127, Including its Effects,on Population Dynamics of Pratylenchus penetrans

A non-chemical technique for surface sterilizing plant-parasitic nematodes for aseptic cultures is described. The method is most applicable to nematodes with active migratory infective stages and requires only a few starting specimens. Rate of achieving a primary aseptic culture with the technique ranged from 60%-100% depending on the conditions of the specimens collected for culturing. Aseptic cultures of species of Meloidogyne, Rotylenchuluz, Pratylenchus, and Radopholus initiated with the method remained contamination-free after 12 months of maintenance in tomato root explant or alfalfa callus cultures. Further studies of Pluronic F127, a polyol gel medium employed in the technique to confine the spread of contaminating bacteria or fungi associated with the nematodes, showed that the polyol gel was a suitable support medium for culturing corn root explant, alfalfa callus tissues, and consequently Pratylenchus species including P. agilis, P. brachyurus, P. scribneri, and P. penetrans. During the course of 10 months, P. penetrans reared in polyol-base medium followed a standard biological growth curve, multiplied to a higher population density, maintained a similar female-to-male ratio, and possessed a similar tendency to reside inside or outside host tissues as did P. penetrans reared in agar-base medium. The percentages of P. penetrans juveniles in the sub-populations residing outside or inside the host tissues reared in polyol-base medium also were similar to and fluctuated temporally in like manner as those reared in agar-base medium. Members of these sub-populations from the polyol- or agar-base were equally infective and reproductive after 9 months of culturing.     

Differential Vertical Movement of Nonvolatile Nematicides in Soil

When incorporated in the top 5-cm of Tifton sandy loam at 11.2 kg/ha in the field, B-68138 [ethyl 4-(methylthio)-m-tolyl isopropyl phosphoramidate] prevented galling of tomato roots by Meloidogyne sp. down to 20 cm. A similar application of 16.8 kg/ha of V-C 9-104 [0-ethyl S,S-dipropyl phosphorodithioate] was 99% effective down to 20 cm. Aldicarb [2-methyl-2-(methylthio) propionaldehyde 0-(methylcarbamoyl) oxime], B-25141 [0,0-diethyl 0-{p-(methylsulfinyl) phenyl}phosphorothioate], and carbofuran [2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate] prevented galling only in the zone of incorporation (top 5-cm of soil). When aldicarb (11.2 kg/ha) was applied to the surface of Ontario fine sandy loam contained in clay pots in the greenhouse, it prevented galling of tomato roots down to 20 cm deep. V-C 9-104 and B-68138, applied similarly, were 100% effective to a depth of 5 cm. B-25141 was 100% effective in the zone of incorporation only. D-1410 [S-methyl-l-(dimethylcarbamoyl)-N-l(methylcarbamoyl)oxy] thioformimidatel did not control 100% of the root-knot nematodes at any depth.     

Morphological Observations of Pratylenchus penetrans from Celery and Strawberry in Southern Ontario

Pratylenchus penetrans was obtained from Premier strawberry in Norfolk County and the Niagara Peninsula and from celery in the latter area. Host affected the dimensions of P. penetrans to a greater extent than geographical area in Ontario. Adults of P. penetrans from southern Ontario tended to be smaller than those reported elsewhere. The presence of three lip annules was consistent in the seven populations studied, although in some specimens one of the annules did not entirely encompass the head. Crenations around the tail tip of females of P. penetrans was common in the populations studied. Not all of the morphological characters were proportional in size to length of the females of P. penetrans.     

Reproduction of Pratylenchus penetrans on Potato and Crops Grown in Rotation with Potato

The relative suitability of potato and crops frequently grown in rotation with potato as hosts for Pratylenchus penetrans was evaluated. Suitability of rye, wheat, corn, oat, sorgho-sudangrass, and potato were compared in pot studies based on ratios of final population : initial population density and densities of nematodes in roots at harvest. Population densities increased more on potato, oat, and corn than on rye, wheat, and sorgho-sudangrass. There were no differences among the four rye cultivars or between the two oat cultivars in host suitability. Population increases were not related to root weight or consistently to nematode densities in roots. Although rye and wheat were equally suitable hosts in pot studies, P. penetrans increased more on wheat than on rye in a field study, indicating that reproduction was reduced or mortality was increased on rye under field conditions.     

A Semiquantitative Method for Enumerating and Observing Parasites and Predators of Soil Nematodes

A laboratory method was developed to count and observe antagonists of soil nematodes and simulate their relationships in the soil. A 10- to 25-cc soil sample is suspended in water and washed through a series of small standard sieves. Residues are washed into a small beaker and collected on a 24-mm filter paper disk in a filter holder under vacuum. The disk is placed on corn meal agar in a petri dish. Microfauna and flora present in the sample colonize the organic matter on the disk and move onto and into the agar where they can be observed easily. Distinct successions of organisms usually occur and within 6-18 days or more, parasites and predators of nematodes are often abundant, especially nematode-trapping fungi. Counting predation events and parasitized nematodes in replicate dishes after specific incubation periods allows quantitative comparisons between soil samples. The method has distinct advantages over others for enumerating organisms which attack nematodes.