Accelerated Degradation of Aldicarb and Its Metabolites in Cotton Field Soils

The degradation of aldicarb, and the metabolites aldicarb sulfoxide and aldicarb sulfone, was evaluated in cotton field soils previously exposed to aldicarb. A loss of efficacy had been observed in two (LM and MS) of the three (CL) field soils as measured by R. reniformis population development and a lack of cotton yield response. Two soils were compared for the first test—one where aldicarb had been effective (CL) and the second where aldicarb had lost its efficacy (LM). The second test included all three soils: autoclaved, non-autoclaved and treated with aldicarb at 0.59 kg a.i./ha, or not treated with aldicarb. The degradation of aldicarb to aldicarb sulfoxide and then to aldicarb sulfone was measured using high-performance liquid chromatography (HPLC) in both tests. In test one, total degradation of aldicarb and its metabolites occurred within 12 days in the LM soil. Aldicarb sulfoxide and aldicarb sulfone were both present in the CL soil at the conclusion of the test at 42 days after aldicarb application. Autoclaving the LM and MS soils extended the persistence of the aldicarb metabolites as compared to the same soils not autoclaved. The rate of degradation was not changed when the CL natural soil was autoclaved. The accelerated degradation was due to more rapid degradation of aldicarb sulfoxide and appears to be biologically mediated.     

Accelerated Degradation of Fenamiphos and Its Metabolites in Soil Previously Treated with Fenamiphos

The degradation of fenamiphos, fenamiphos sulfoxide, and fenamiphos sulfone was determined in a greenhouse experiment using autoclaved and nonautoclaved soil from field plots treated or not treated with fenamiphos. Fenamiphos degradation and formation of fenamiphos sulfoxide was faster in uonautoclaved soil than in autoclaved soil. In nonautoclaved soil, previous exposure to fenamiphos was associated with increased rate of degradation of fenamiphos snlfoxide. Fenamiphos total toxic residue degraded more rapidly in nonautoclaved soil previously exposed to fenamiphos than in nonautoclaved soil never exposed to fenamiphos. This accelerated degradation was due to more rapid degradation of fenamiphos sulfoxide and appears to be biologically mediated.     

Efficacy of Ethoprop on Meloidogyne hapla and M. chitwoodi and Enhanced Biodegradation in Soil

Responses of egg masses, free eggs, and second-stage juveniles (J2) ofMeloidogyne hapla and M. chitwoodi to ethoprop were evaluated. The results indicated that J2 were the most sensitive, followed by free eggs and egg masses. In general, M. chitwoodi was more susceptible to ethoprop than M. hapla. Ethoprop at 7.2 μg a.i./g soil protected tomato roots from upward migrating M. chitwoodi for 5 weeks. The zone of protection was extended to 10 and 20 cm below the root zone when 3.6 and 7.2 cm water were applied over 8 days. Ethoprop at 1.8, 3.6, and 7.2 μg a.i./g soil degraded faster and killed fewer M. chitwoodi J2 in potato field soil previously exposed to ethoprop than in unexposed soil or sterilized exposed soil. The enhanced biodegradation property of the exposed soil lasted 17 months after the last application of ethoprop. The limited downward movement of ethoprop in the soil, migration of M. chitwoodi J2 into the treated zone, presence of resistant life stage(s) at the time of application, and loss of efficacy due to enhanced biodegradation may have a significant effect on the performance of ethoprop.     

Effects of Soil Moisture on Control of Heterodera schachtii with Aldicarb

Soil moisture and the nematode population density in aldicarb-treated soil influenced control of the sugarbeet nematode, Heterodera schachtii. Greater numbers of nematode larvae infected 14-day-old sugarbeet seedlings growing in aldicarb-treated soil at 20-30% than at 80-100% field capacity (F. C.), and plant growth was inversely related to nematode infection and the nematode population density. Compared with that of control plants, plant growth increase also was greater at 80-100% F. C. when the nematode population was above 1.8 larvae/gm soil. A nematode population of 1.8 larvae/gm soil did not significantly affect sugarbeet yields. Aldicarb gave less control when soil moisture levels dropped to 20 and 50% F. C. at nematode populations of 3.5 and 6.2 larvae/gm soil. More effective control was obtained wth soil moisture levels at or above 80% F. C. This difference was attributed to continued activity of the toxicant in the rhizosphere at the high moisture level.     

Residues of Aldicarb and its Oxides in Beta vulgaris L. and Systemic Control of Heterodera schachtii

Altlicarb residues in foliage of Beta vulgaris L. 21 days after transplanting to soil treated with 1-5 μg aldicarb/g soil were proportional to residues in storage roots, but 20 times as great. Initial concentrations of residues in roots 21 days after treatment were proportional to applied rates but declined by 56% when roots were stored 25 days at 24 C. Mean respective concentrations of aldicarb, aldicarb sulfoxide, and aldicarb sulfone were 8.7, 81.6, and 9.8% of the total residues. In separate tests, equivalent concentrations of toxic carbamates in roots resulted in similar levels of control of Heterodera schachtii. Systemic levels that completely suppressed development of females and males on sectioned roots were respectively 0.35 and 0.8 μg/g of root tissue.     

Growth and Yield Responses of Soybean to Aldicarb

A series of greenhouse, phytotron, field, and microplot experiments evaluated factors that influenced plant-growth.stimulation associated with the use of the pesticide aldicarb. A phytotron experiment showed.that aldicarb increased growth, of Ransom soybean at all temperatures but was somewhat phytotoxic to Coker 156 soybean at 30 C. Soybean gave the greatest response to this nematicide at 22 C in a commercially available medium, Metromix 220. Soybean cultivars Ransom and Coker 156. exhibited increased growth in response to aldicarb or, to a lesser extent aldicarb sulfone treatments under greenhouse and microplot conditions. Enhanced soybean growth, however, did not always result in significantly greater soybean seed yield. Soil type affected soybean sensitivity to aldicarb, with. the greatest growth and yield increases generally occurring in fine-textured soils or those with high.organic matter. Plant-growth stimulation by aldicarb occurs in the absence of pests but is dependent upon concentration and edaphic and other environmental factors.     

Efficacy of Aldicarb to Rotylenchulus reniformis and Biodegradation in Cotton Field Soils

The microbial degradation of aldicarb was examined in the greenhouse using soil from four cotton fields with a history of aldicarb use. The addition of aldicarb at 0.59 kg a.i./ha to natural soil increased Rotylenchulus reniformis numbers 6.6% in one soil and decreased R. reniformis numbers only 25.8% in another soil as compared to the corresponding natural soil without aldicarb. The use of increasing rates of aldicarb did not increase the efficacy of aldicarb in these soils. Rotylenchulus reniformis numbers were reduced 39.8, 22.6, and 6.8%, and increased 5.7% for aldicarb applied at 0.29, 0.59, 0.85, and 1.19 kg a.i./ha, respectively, in one natural soil. In another natural soil, R. reniformis numbers were reduced 42.5 and 21.9% for aldicarb applied at 0.29 and 1.19 kg a.i./ha, respectively, but increased 19.1 and 10.6% for aldicarb applied at 0.59 and 0.85 kg a.i./ha, respectively. Autoclaving the soils restored aldicarb toxicity in both soils, and R. reniformis numbers were reduced 96 and 99%, respectively, as compared to autoclaved soil without aldicarb. Bacterial populations were greater in the natural soils where aldicarb did not reduce R. reniformis numbers relative to the same soils that were autoclaved. However, no bacterial species was consistently associated with aldicarb degradation.     

Effects of Aldicarb and Fenamiphos on Acetycholinesterase and Motility of Caenorhabditis elegans

The ability of Caenorhabditis elegans to recover from exposure to high doses of aldicarb and fenamiphos was examined at the organismal and biochemical levels by determination of movement and acetylcholinesterase activity. Nematodes recovered rapidly from a 24-hour exposure to both compounds at concentrations that caused complete paralysis. Acetylcholinesterase regained nearly full activity after a 24-hour exposure to aldicarb but only 10% activity after exposure to fenamiphos. The nematodes were able to move normally, however, on the limited activity that was regained after fenamiphos treatment. Mutant C. elegans strains deficient in various molecular forms of acetylcholinesterase were utilized to demonstrate that the mechanism of recovery did not involve new synthesis of enzyme. This result was confirmed by experiments on acetylcholinesterase reactivation from live versus dead nematodes.     

Influence of Aldicarb on the Growth and Yield of Tobacco

Microplot and field experiments were used to examine the plant-growth stimulation frequently associated with the use of aldicarb on tobacco in the absence of major pests. Aldicarb rates of 1.5-4.5 kg a.i./ha enhanced tobacco growth and yield in most experiments, but higher rates (≥ 4.5 kg) usually resulted in a neutral to negative effect. Tobacco cultivars NC 82 and Speight G-28 were more responsive than McNair 944 to the pesticide in microplots. Supplemental irrigation enhanced the responsiveness of Speight G-70 tobacco and McNair 944 to aldicarb, but excessive moisture (ca. 7-8 cm/week) limited cured-leaf yields. Aldicarb also resulted in the greatest mean tobacco yields in 35 field experiments involving Meloidogyne spp. over 3 years, relative to ethoprop, 1,3-dichloropropene (1,3-D), 1,3-D + chloropicrin, and nontreated controls. Thus, aldicarb generally enhanced tobacco growth and yield in the presence or absence of nematodes, but its impact is dependent on other variables, including cultivar, soil moisture, and soil type.     

Effects of Aldicarb on the Behavior of Heterodera schachtii and Meloidogyne javanica

The toxic effects of sublethal concentrations ofaldicarb were studied on eggs and second-stage larvae and males of Heterodera schachtii and second-stage larvae only of Meloidogyne javanica in a quartz sand substrate. Aldicarb was more toxic to eggs of H. schachtii than to those of M. javanica. Complete suppression of hatching occurred between 0.48 and 4.8 μg/ml aldicarb for H. schachtii whereas 100% inhibition of hatch of M. javanica occurred between 4.8 and 48.0 μg/ml. M. javanica hatch was stimulated at 0.48 μg/ml aldicarb. Migration of second-stage larvae of H. schachtii and M. javanica in sand columns was inhibited under continuous exposure to 1 μg/ml aldicarb. Infection of sugarbeet and tomato seedlings by larvae was inhibited at 1 μg/ml. H. schachtii males failed to migrate toward nubile females at 0.01 μg/ml aldicarb. This was partially confirmed in a field study in which adding aldicarb to soil resulted in fewer females being fertilized.     

Effects of Aldicarb and Its Sulfoxide and Sulfone on the Biology of Tylenchulus semipenetrans

In laboratory testing, egg hatch of Tylenchulus semipenetrans was stimulated at concentrations of 1 and 10 μg/ml aldicarb solution and inhibited at 50 and 100 μg/ml. Aldicarb was more inhibitory to egg hatch than the aldicarb sulfoxide and the aldicarb sulfone. Inhibition of hatch at the high concentration was associated with delays in the molting processes, lack of larval movement within the egg, and delays in embryonic development. Nematode motility was reduced at 10, 50, and 100 μg/ml of aldicarb and aldicarb sulfoxide solution, and at 50 and 100 μg/ml aldicarb sulfone. Male development was retarded at 10 μg/nrl and almost completely inhibited at 50 and 100 μg/ml of the three chemicals. In greenhouse tests, female development antl reproduction on roots of citrus seedlings were suppressed by aldicarb at rates of 2.6 μg/ml and completely inhibited at 10.6 μg/ml of soil solution during a 50-day experimental period. Under field conditions, there was little systemic movement of aldicarb into roots located outside treated areas. Aldicarb reduced the nematode larvae and the female adult population in the second year after the second treatment. There were no differences in egg hatch and sex ratio of citrus nematodes between treated and nontreated roots.     

Factors Affecting Furfural as a Nematicide on Turf

Recently a furfural nematicide Multiguard Protect EC was launched for use on turfgrasses in the United States. A series of greenhouse experiments were conducted to determine the concentration and exposure time required for this formulation to irreversibly affect Belonolaimus longicaudatus, and to study factors that might affect the practicality of furfural use in turfgrass systems. One experiment exposed B. longicaudatus to increasing concentrations of furfural (0 to 990 ppm) in vitro for either 24 or 48 hr, followed by inoculation onto bermudagrass. A second experiment evaluated effects of exposure of B. longicaudatus to increasing concentrations of furfural in soil solution on bermudagrass with or without an organic thatch layer. A third experiment evaluated effects on B. longicaudatus of increasing concentrations of furfural applied as a spray treatment to creeping bentgrass. Results from the in vitro exposure experiment found decreasing numbers of B. longicaudatus with increasing furfural concentration beginning with the lowest concentration tested (270 ppm). Belonolaimus longicaudatus were virtually eliminated with furfural concentrations ≥ 720 ppm. Similarly, exposure to increasing concentration of furfural in soil solution resulted in increasing reduction in numbers of B. longicaudatus. Presence of thatch slightly reduced the population density of B. longicaudatus. Spray application of furfural only reduced numbers of B. longicaudatus at the two highest rates (3,600 and 4,950 ppm).     

Degradation of 1,3-Dichloropropene (1,3-D) in Soils with Different Histories of Field Applications of 1,3-D

Laboratory experiments were conducted to determine the mineralization rates of 1,3-dichloropropene (1,3-D) in surface and subsurface soil samples collected from three sites in Florida with different histories of 1,3-D exposure. Mineralization rates of uniformly labeled ¹⁴C-1,3-D in surface and subsurface samples collected from two of the three sites, one of which was treated with 1,3-D only once and the other which had not been treated with the chemical for 5 years, were similar to the corresponding samples collected from untreated plots, and the rates generally decreased with soil depth. Initial mineralization rates in surface and subsurface samples collected from the site that had repeatedly been treated with 1,3-D at least 6 of the past 12 years were more rapid than those in either the corresponding untreated samples or in samples collected from the two other sites. Not only were the initial mineralization rates in soil samples collected from this site greater, but also the disappearance rates of cis- and trans-l,3-D were greater than in the corresponding untreated samples. Trans-1,3-D was degraded much more rapidly in the enhanced soil than was the cis- form. In addition, no or little trans-3-chloroallyl alcohol (CAA), the hydrolysis product of trans-l,3-D, was formed; large amounts of cis-3-CAA, the hydrolysis product of cis-1,3-D, were detected. This suggest that biological hydrolysis is responsible for the hydrolysis of trans-l,3-D to trans-3-CAA in enhanced soil and chemical hydrolysis is responsible for the hydrolysis of cis- and trans-l,3-D to 3-CAA in nonenhanced soil.     

Behavior of Aldicarb in Soil Relative to Control of Heterodera schachtii

The adsorption characteristics of two soils for aldicarb sulfoxide were similar to that described by the Freundlich equation, The adsorption constant for the Holtville clay was 3.3, and that of the Buren silt loam, 0.34. Planting beds in a field of Holtville clay and another of Buren silt loam were side-dressed at 25 kg and 50 kg/ha 10% aldicarb (Temik® 10G). Comparison of field measurements of aldicarb concentrations with previous laboratory determinations of aldicarb effects on Heterodera schachtii allowed predictions of soil zones in which hatching, infectivity, and orientation of males to females would be affected. Aldicarb in the soil water of Holtville clay sufficient to interfere with male orientation extended through most of the bed profile to a depth of 46 cm 1 week after the first irrigation. Orientation could be affected in only the top 20 cm of the bed 37 days after treatment and application of 712 mm of irrigation water. In Buren silt loam, disorientation of males was estimated to occur throughout the bed 42 days after treatment and 600 mm irrigation water. Aldicarb persisted in extensive areas of the bed at concentrations sufficient to prevent infection. In small areas of the profile, aldicarb sufficient to inhibit hatching persisted. Amounts of aldicarb in soil water samples obtained directly from beds agreed well with those from the analysis of the air dried soil samples.     

Population Changes of Heterodera glycines and Soybean Yields Resulting from Soil Treatment with Alachlor,Fenamiphos, and Ethoprop

The population dynamics of Heterodera glycines as influenced by alachlor, fenamiphos, and ethoprop alone and in herbicide-nematicide combinations were studied in the field. Numbers of H. glycines juveniles and eggs were higher at midseason and harvest where nematicides were applied. Fenamiphos alone or in combination with alachlor provided better control of H. glycines and greater seed yields than treatments with ethoprop. Numbers of H. glycines eggs at harvest in 1980 were positively correlated with numbers of juveniles at planting in 1981 and negatively related to seed yield in 1981.     

Effects of Site-specific Application of Aldicarb on Cotton in a Meloidogyne incognita-infested Field

Cotton farmers in Missouri commonly apply a single rate of aldicarb throughout the field at planting to protect their crop from Meloidogyne incognita, even though these nematodes are spatially aggregated. Our purpose was to determine the effect of site-specific application of aldicarb on cotton production in a field infested with these nematodes in 1997 and 1998. Cotton yields were collected from sites not treated with aldicarb (control), sites receiving aldicarb at the standard recommended rate of 0.58 kg a.i./ha, and sites receiving specific aldicarb rates based on the soil population densities of second-stage infective juveniles of root-knot nematode. Yields for the standard rate and site-specific rate treatments were similar and greater (P ≤ 0.05) than the control treatment. Less aldicarb was used for the site-specific than the uniform-rate treatment each year—46% less in 1997 and 61% less in 1998. Costs associated with the site-specific treatment were very high compared with the uniform-rate treatment due to a greater number of soil samples analyzed for nematodes. Site-specific application of aldicarb for root-knot nematode management in cotton may pose fewer environmental risks than the uniform-rate application of aldicarb.     

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.     

Nematicidal screening of essential oils and potent toxicity of Dysphania ambrosioides essential oil against Meloidogyne incognita in vitro and in vivo

It is known that some plant essential oils have pesticide activities. Among the 29 oils evaluated in this study, 14 showed nematicidal activities of 8 to 100% at the concentration of 1,000 μg/ml, compared with a control of 0.01 g/ml Tween 80^®. At a lower concentration of 500 μg/ml, only Dysphania ambrosioides oil caused >90% mortality of second‐stage juveniles (J2) of Meloidogyne incognita. The LC₅₀ and LC₉₅ values for D. ambrosioides oil were 307 μg/ml and 580 μg/ml, respectively. M. incognita eggs placed in D. ambrosioides oil solutions had a significant reduction in J2 hatching compared with controls. Therefore, the oil had a toxic effect on both eggs and J2 of M. incognita. This was in contrast to nematicides on the market that act efficiently only on J2. When J2 were placed in D. ambrosioides oil at its LC₅₀ concentration and inoculated onto tomato plants, the reduction in numbers of galls and eggs was 99.5% and 100%, respectively. Dysphania ambrosioides oil applied to the potting substrate of plants at a concentration of 1,100 μg/ml significantly reduced the number of galls and eggs of M. incognita, whereas a concentration of 800 μg/ml only reduced the number of eggs compared with the controls (Tween 80^® and water). The main components of the D. ambrosioides oil detected by gas chromatography–mass spectrometry were (Z)‐ascaridole (87.28%), E‐ascaridole (8.45%) and p‐cymene (3.35%), representing 99.08% of the total oil composition. Given its nematicidal activity, D. ambrosioides oil represents an exciting raw material in the search for new bioactive molecules for the pesticide industry.     

Factors Affecting the Control of Rotylenchulus reniformis with Electromagnetic Energy

The reniform nematode Rotylenchulus reniformis was reduced in the upper 10 cm of soil with application of UHF electromagnetic energy. Bioassay of treated soil indicated no delayed effect on the population from the treatment. The population was significantly reduced by hot water treatments at 40 C for 10 min, and at 45 C for 5 and 10 min, 50 C and above killed all nematodes. Data were inconclusive as to whether the effect of UHF electromagnetic energy was thermal or nonthermal.     

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.