Nematicidal Effects of Oxamyl Applied to Leaves of Banana Seedlings

Foliar applications of oxamyl prevented nematodes from invading roots of diploid bananas. One spray with 1,250 μg/ml was more effective than 1, 2, or 3 sprays with 625 μg/ml applied at 5-day intervals. After 3 sprays with 1,250 μg/ml, invasion may be prevented for up to 4 weeks and possibly longer. Washing roots after oxamyl treatments prevented nematicidal control. When applied to nematode-infected plants, three sprays of oxamyl decreased nematode populations in the roots.     

Nematostatic Activity of Oxamyl and N,N-Dimethyl-1-cyanoformamide (DMCF) on Meloidogyne incognita Juveniles

The nematostatic activity of oxamyl, methyl-N'',N''-dimethy]-N-hydroxy-l-thiooxamimidate (oxamyl-oxime) and N,N-dimethyl-l-cyanoformamide (DMCF) was studied by immersing 10 Meloidogyne incognita second-stage juveniles into aqueous solutions of various concentrations of each chemical. At concentrations of 500 to 8,000 μg/ml, oxamyl quickly immobilized immersed juveniles. In all other concentrations studied (down to 4 μg/ml), oxamyl stopped or reduced movement of juveniles within 24 hours. DMCF also quickly immobilized juveniles at concentrations of 4,000 and 8,000 μg/ml and reduced movement at 2,000 μg/ml. Lower concentrations had no observed effect on movement. In solutions of the oxime from 2,000 to 8,000 μg/ml, some reduction of movement was observed, but most juveniles maintained some motion over a period of 24 hours. Juveniles were transferred to water from 4,000 μg/ml solutions of oxamyl and DMCF after various intervals of time in order to determine the effect of duration of exposure to the chemicals on the ability of the immobilized juveniles to recover normal motion. Some recovery was observed even after 24 hours of exposure to DMCF, but none after exposure to oxamyl for longer than 40 minutes.     

Nematicide Treatments of Turfgrass Seed

Seed treatments of improved Kentucky bluegrass and fescue cultivars with carbofuran, oxamyl, and phenamiphos dissolved in acetone reduced seedling emergence, but treatments were not extremely phytotoxic. Phenamiphos was the most toxic, particularly at the 5,000 μg/ml concentration. Fresh weight of grass clippings 35 d following planting generally was greater in treatments than in controls except for the 5,000 μg/ml phenamiphos treatments on certain cultivars. All nematicide seed treatments reduced the number of Pratylenchus penetrans subsequently recovered from Pennlawn creeping red fescue roots 4-5 wk after treatment. The infusion of nematicides into grass seed with organic solvents appears to be an effective means of reducing nematode damage to turfgrass seedling with little environmental hazard.     

Control of Globodera rostochiensis in Relation to Method of Applying Nematodes

Soaking potato tuber pieces for 15 min in 8,000 μg/ml of oxamyl just before planting reduced the number of Globodera rostochiensis cysts that developed on potato roots, but this treatment was phytotoxic. Five foliar applications of 1.12 kg a.i./ha of oxamyl or carbofuran at 10-day intervals beginning when 90% of the plants had emerged suppressed increase in G. rostochiensis densities. Similar foliar applications of phenamiphos were ineffective in controlling G. rostochiensis. Soil applications (in the row at planting) of aldicarb, carbofuran, phenamiphos, ethoprop, and oxamyl at 5.6 kg a.i./ha reduced the numbers of white females that developed on potato roots, but only those treatments involving aldicarb and oxamyl suppressed G. rostochiensis population increase. Combined soil and foliar treatments did not provide any advantage over soil treatment alone, as soil applications of 5.6 kg a.i./ha alone were equal to, or better than, combined soil (3.4 kg a.i./ha) and foliar (2.2 kg a.i./ha) applications in controlling G. rostochiensis.     

Effects of Oxamyl on the Citrus Nematode,Tylenchulus semipenetrans,and on Infection of Sweet Orange

Foliar sprays of 4 μg/ml oxamyl on sweet orange trees in a greenhouse slightly depressed the number of Tylenchulus semipenetrans larvae obtained from roots and soil, but similar treatments were not effective in two orchards. Soil drench treatments decreased the number of citrus nematode larvae obtained from roots or soil of citrus plants grown itt a greenhouse and in orchards. Exposure to 5-10 μg/ml of oxamyl in water was lethal to only a few second-stage larvae treated 10 days, and many second-stage larvae in 2.0 μg/ml oxamyl recovered motility when transferred to fresh water. Aqueous solutions of 50 and 100 μg/ml of oxamyl were toxic to citrus nematode larvae. Additional observations indicate that oxamyl interfered with hatch of citrus nematode larvae and was nematistatic and/or protected sweet orange roots from infection. Oxamyl degraded at different rates in two soils. The number of citrus nematode larvae that infected and developed on sweet orange roots was increased by an undetermined product of the degradation of oxamyl in soil, water, and possibly within plants. This product apparently was translocated in roots.     

In Vitro Hatch and Survival of Heterodera glycines as Affected by Alachlor and Phenamiphos

Heterodera glycines (race 1) eggs were exposed to aqueous solutions o f selected concentrations o f the herbicide alachlor and the organophosphate nematicide phenamiphos alone and in herbicide-nematicide combinations. Phenamiphos (0.5 μg/ml) + alachlor (0.063, 0.125, or 1.0 μg/ ml) treatments increased the incidence o f juvenile hatch over that of untreated controls at 18 days. At 18 and 25 days, phenamiphos (0.5 μg/ml) treatments contained more juveniles than did phenamiphos at 1.0 μg/ml. Phenamiphos (1.0 μg/ml) alone and in combination with alachlor (1.0 μg/ ml) suppressed hatch for 21 days and juvenile survival for more than 21 days. Alachlor treatments enhanced juvenile survival compared to the untreated control at 14 and 21 days. Technical alachlor gave results similar to those of the formulated product.     

Influence of Water and Soil Temperature on the Concentration and Efficacy of Phenamiphos for Control of Root-Knot Nematodes

Field plots of Tifton loamy sand were treated with phenamiphos for control of root-knot nematodes in a multiple-crop system of turnips, field corn, and southern peas. Preplant applications of phenamiphos protected roots of turnips and corn from damage by root-knot nematodes. Concentrations of phenamiphos at application in the 0-15-cm soil layer were near 6 μg/g on turnips and near 4 μg/g on corn and southern peas. After 30 d, concentrations were approximately 1 μg phenamiphos/g of soil for all crops. Concentrations of 2.0-3.8 μg phenamiphos/g of soil for 9-d duration appeared to be adequate for control of root-knot nematodes on field corn and southern peas in this multiple-crop system. Stepwise regression analyses indicated that 31%, 62%, and 22% of the variations in concentration of phenamiphos in the soil planted to turnips, corn, and southern peas, respectively, were attributable to the amount of water that the plots received. Soil temperature had no effect on concentrations of phenamiphos.     

Effects of Selected Nematicides on Hatching of Heterodera schachtii

Aldicarb, carbofuran, fensulfothion, and phenamiphos were tested in concentrations of 1-100 μg/ml for their effects on hatching of Heterodera schachtii. Exposure of cysts to 1 μg aldicarb or carbofuran/ml stimulated hatch whereas phenamiphos and, to a lesser degree, fensulfothion inhibited hatch. Addition of aldicarb to sugarbeet root diffusate or 4 mM zinc chloride suppressed activities of these hatching agents. Transfer of cysts previously treated with aldicarb or carbofuran to zinc chloride or water rapidly initiated hatch which finally exceeded the hatch from cysts not treated with the nematicides.     

Root Cortical Cell Spherical Bodies Associated with an Induced Resistance Reaction in Monoxenic Cultures of Meloidogyne incognita

The root-knot nematode Meloidogyne incognita was monoxenically cultured on excised roots of soybean cv. Pickett and tomato cv. Rutgers in agar media containing either 0 to 1,600 μg/ml ammonium nitrate or 0 to 100 μg/ml urea. Observations with scanning and transmission electron microscopy indicated that an elevated concentration of ammonium nitrate or urea inhibited giant cell formation and suppressed nematode development in the infected soybean roots. In the tomato roots, concentrations of ammonium nitrate above 400 μg/ml or urea above 25 μg/ml inhibited giant cell formation and nematode development. Coincident with the nitrogen concentrations that suppressed giant cell formation was the appearance of electron-dense spherical bodies in the cortical parenchyma cells of both the soybean and tomato roots. These bodies, which were 1-4 μm in diameter, appeared to form in the cytoplasm and migrate to the cell vacuole.     

Effect of Phenamiphos on Heterodera schachtii and Meloidogyne javanica

Aqueous solutions of technical-grade phenamiphos [ethyl 3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoratnidale] were used in hatching chambers to test, under laboratory tory conditions, the effect of phenamiphos on the hatching and movement of Meloiclogyne javanica and Heterodera schachtii. Hatch of M. javanica and H. schachtii eggs was depressed 70 and 88% by nematicide at 0.48 and 4.80 μg/ml, respectively. The infectivity of second-stage larvae of both species was affected by concentrations as low as 0.01 μg/ml. At least 0.5 μg/ml was required to decrease the movement of larvae of M. javanica and H. schachtii. To decrease the movement of H. schachtii males toward females, 10 μg/ml was required. In a field experiment using a 15% granular formulation, 5 kg/ha a.i. significantly reduced infection of sugarbeet roots by H. schachtii.     

Growth of Potato and Control of Pratylenchus penetrans with Oxamyl-treated Seed Pieces in Greenhouse Studies

Oxamyl was applied to both uncut and cut potato tubers in aqueous solutions of 1,000 to 32,000 μg/ml. Emergence in greenhouse pots was delayed for a day or more after soaking cut tuber pieces in 32,000 μg/ml. After 10 weeks plant growth was greater, relative to the control, when Pratylenchus penetrans-infested soil was planted with cut tubers soaked for 20 minutes in 32,000 μg/ml. Soaking for 40 minutes did not increase nematode control nor affect plant growth. Oxamyl applied to tubers at 1,000 μg/ml reduced the numbers of P. penetrans in the soil by 20% and in the roots by 35%; at 32,000 μg/ml, the numbers of P. penetrans in the soil were reduced by 73-86% and in the roots by 86-97%. The numbers of P. penetrans did not increase in the roots of plants developed from cut tubers soaked in 32,000 μg/ml over a period of 10 weeks, but numbers of lesion nematodes had begun to increase in the soil.     

A Bioassay to Estimate Root Penetration by Nematodes

An in vitro bioassay with a 96-well microtiter plate was used to study the effect of lectins on burrowing nematode penetration of citrus roots. In each well, one 4-mm root segment, excised from the zone of elongation of rough lemon roots, was buried in 0.88 g dry sand. Addition of a Radopholus citrophilus suspension containing ca. 300 nematodes in 50 μ1 test solution completely moistened the sand in each well. The technique assured uniform treatment concentration throughout the medium. Within 16-24 hours, burrowing nematodes penetrated citrus root pieces, primarily through the cut ends. The lectins (100 μg/ml) Concanavalin A (Con A), soybean agglutinin (SBA), wheat germ agglutinin (WGA), and Lotus tetragonolobus agglutinin (LOT) stimulated an increase in penetration of citrus root segments by Radopholus citrophilus. Concentrations as low as 12.5 μg/ml Con A, LOT, and WGA stimulated burrowing nematode penetration of citrus roots. Heat denaturation of the lectins reversed their effect on penetration; however, incubation of nematodes in lectin (25 μg/ml) with 25 mM competitive sugars did not. The reason for enhanced penetration associated with lectins is unclear.     

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

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

Interaction of Vesicular-arbuscular Mycorrhizal Fungi and Phosphorus with Meloidogyne incognita on Tomato

The influence of two vesicular-arbuscular mycorrhizal fungi and phosphorus (P) nutrition on penetration, development, and reproduction by Meloidogyne incognita on Walter tomato was studied in the greenhouse. Inoculation with either Gigaspora margarita or Glomus mosseae 2 wk prior to nematode inoculation did not alter infection by M. incognita compared with nonmycorrhizal plants, regardless of soil P level (either 3 μg [low P] or 30 μg [high P] available P/g soil). At a given soil P level, nematode penetration and reproduction did not differ in mycorrhizal and nonmycorrhizal plants. However, plants grown in high P soil had greater root weights, increased nematode penetration and egg production per plant, and decreased colonization by mycorrhizal fungi, compared with plants grown in low P soil. The number of eggs per female nematode on mycorrhizal and nonmycorrhizal plants was not influenced by P treatment. Tomato plants with split root systems grown in double-compartment containers which had either low P soil in both sides or high P in one side and low P in the other, were inoculated at transplanting with G. margarita and 2 wk later one-half of the split root system of each plant was inoculated with M. incognita larvae. Although the mycoorhizal fungus increased the inorganic P content of the root to a level comparable to that in plants grown in high P soil, nematode penetration and reproduction were not altered. In a third series of experiments, the rate of nematode development was not influenced by either the presence of G. margarita or high soil P, compared with control plants grown in low P soil. These data indicate that supplemental P (30 μ/g soil) alters root-knot nematode infection of tomato more than G. mosseae and G. margarita.     

Effects of Selected Insecticides and Nematicides on the In Vitro Development of the Entomogenous Nematode Neoaplectana carpocapsae

The effects of organophosphates (mevinphos, phenamiphos, trichlorfon), carbamates (carbofuran, methomyl, oxamyl), a formamidine (chlordimeform), a synthetic pyrethroid (fenvalerate), a chlorinated hydrocarbon (methoxychlor). and an insect growth regulator (diflubenzuron) on in vitro development and reproduction of Neoaplectana carflocapsae were tested by incorporating each chemical into a nematode rearing medium. Organophosphates and carbamates adversely affected development and reproduction at concentrations ≥ 0.1 mg/ml. Phenamiphos was the most toxic, with no nematode reproduction at 0.01 mg/ml. Inoculated infective juveniles developed to adults with some of the organophosphates and carbamates, but limited or no reproduction occurred. Chlordimeform inhibited development at 1.0 mg/ml, while diflubenzuron, fenvalerate, and methoxychlor did not significantly (P > 0.05) reduced reproduction at 1.0 mg/ml. The organophosphate and carbamate nematicides in use for control of plant-parasitic nematodes may be toxic to N. carpocapsae in the soil.     

Management of Globodera rostochiensis as Influenced by Nematode Population Densities and Soil Type

The effects of aldicarb, oxamyl, 1,3-D, and plastic mulch (solarization) on soil population densities of the golden nematode (GN) Globodera rostochiensis was assessed in field and microplot experiments with different soil types. Oxamyl was evaluated in both soil and foliar treatments, whereas aldicarb, 1,3-D, and solarization were applied only to soil. Soil applications of aldicarb and oxamyl resulted in reduced nematode populations after GN-susceptible potatoes in plots with initial population densities (Pi) of > 20 and 7.5 eggs/cm³ soil, respectively, but nematode populations increased in treated soil when Pi were less than 20 and 7.5 eggs/cm³soil. In clay loam field plots with Pi of 19-76 eggs/cm³ soil, nematode densities increased even with repeated foliar applications of oxamyl, whereas nematode populations at Pi greater than 76 eggs/cm³ soil were reduced by foliar oxamyl. Treatment with 1,3-D or solarization, singly or in combination, reduced GN soil population densities regardless of soil type or Pi. Temperatures lethal to GN were achieved 5 cm deep under clear plastic but not 10 or 15 cm deep.     

Sensitivity of Meloidogyne incognita and Rotylenchulus reniformis to Abamectin

Avermectins are macrocyclic lactones produced by Streptomyces avermitilis. Abamectin is a blend of B_1a and B_1b avermectins that is being used as a seed treatment to control plant-parasitic nematodes on cotton and some vegetable crops. No LD₅₀ values, data on nematode recovery following brief exposure, or effects of sublethal concentrations on infectivity of the plant-parasitic nematodes Meloidogyne incognita or Rotylenchulus reniformis are available. Using an assay of nematode mobility, LD₅₀ values of 1.56 μg/ml and 32.9 μg/ml were calculated based on 2 hr exposure for M. incognita and R. reniformis, respectively. There was no recovery of either nematode after exposure for 1 hr. Mortality of M. incognita continued to increase following a 1 hr exposure, whereas R. reniformis mortality remained unchanged at 24 hr after the nematodes were removed from the abamectin solution. Sublethal concentrations of 1.56 to 0.39 μg/ml for M. incognita and 32.9 to 8.2 μg/ml for R. reniformis reduced infectivity of each nematode on tomato roots. The toxicity of abamectin to these nematodes was comparable to that of aldicarb.     

A Nematicide Seed Treatment to Control Ditylenchus dipsaci on Seedling Alfalfa

Three nematicides were evaluated as seed treatments to control the alfalfa stem nematode (Ditylenchus dipsaci) on seedling alfalfa. Alfalfa seeds were soaked for 10 hours in a 0.5% (formulated by weight) concentration of either carbofuran, phenamiphos or oxamyl in acetone with no adverse effect on seed germination. All three treatments decreased nematode damage and increased survival of ''Ranger'' (susceptible) and ''Lahontan'' (resistant) alfalfa plants, when seeds were planted in soil infested with D. dipsaci. Mean live plant counts after 6 weeks in the untreated control, acetone alone, carbofuran, phenamiphos, and oxamyl treatments, respectively, were 4.3, 6.3, 19.0, 19.8, and 19.0 for Lahontan and 4.5, 1.5, 18.5, 19.3, and 18.0 for Ranger from 20 seeds/pot. Nematicide seed treatments resulted in significantly healthier Ranger alfalfa plants 4 months after planting. The combination of seed treatment and host resistance may provide a means of establishing alfalfa in an alfalfa monocropped system where soil populations of D. dipsaci are high.     

Evaluation of the Protective and Therapeutic Properties of DBCP for Control of Root-Knot Nematode on Tomato

Twelve soil drenches over a period of 30 days with DBCP concentrations of 40 μg/ml did not completely prevent infection of tomato plants by root-knot nematode juveniles. Repeated DBCP drenches of 40 μg/ml halted gall development during the drenches, but 10 days after drenching was discontinued galls were apparent. DBCP drenches at 200 μg/ml prevented tomato root development, and 40 μg/ml slowed it. Ten μg/ml increased the height of root-knot-infected plants, but not their top weights. Treated plants were lanky. Protective drenches of 2.5 to 40 μg/ml of DBCP decreased nematode populations and increased fruitfulness. DBCP as a therapeutant reduced the incidence of galling on new roots and halted increases in gall size on previously infected roots but did not improve fruitfulness or plant size significantly.     

Nicotine Content of Tobacco Roots and Toxicity to Meloidogyne incognita

The motility of Meloidogyne incognita second-stage juveniles (J2) and their ability to induce root galls in tomato were progressively decreased upon exposure to nicotine at concentrations of 1-100 μg/ml. EC₅₀ values ranged from 14.5 to 22.3 μg/ml, but J2 motility and root-gall induction were not eliminated at 100 μg/ml nicotine. Nicotine in both resistant NC 89 and susceptible NC 2326 tobacco roots was increased significantly 4 days after exposure to M. incognita. The increase was greater in resistant than in susceptible tobacco. Root nicotine concentrations were estimated to be 661.1-979.1 μg/g fresh weight. More M. incognita were detected in roots of susceptible than in roots of resistant tobacco. Numbers of nematodes within resistant roots decreased as duration of exposure to M. incognita was increased from 4 to 16 days. Concentrations of nicotine were apparently sufficient to affect M. incognita in both susceptible and resistant tobacco roots. Localization of nicotine at infection sites must be determined to ascertain its association with resistance.