Soybean Foliage Research Articles

Effects of Heat-Sensitive Agents, Soil Type, Moisture, and Leaf Surface on Persistence ofAnticarsia gemmatalis(Lepidoptera: Noctuidae) Nucleopolyhedrovirus

In a laboratory experiment, persistence of Anticarsia gemmatalis Hubner nucleopolyhedrovirus (AgNPV) was significantly lower in marsh soil than in agricultural soil. AgNPV was inactivated significantly more quickly in soil at −0.3 bar water potential than in soil at water potentials of 0 bar or −5 bar. Loss of AgNPV activity was significantly faster in unautoclaved soil than in autoclaved soil. AgNPV stored in unautoclaved marsh water lost 99% of its activity within 64 d, whereas AgNPV in distilled water or autoclaved marsh water remained 98–99% active after the same time period. The soil and marsh-water results indicate that 1 or more heat-sensitive agents, perhaps microorganisms, were inactivating AgNPV. The persistence of AgNPV was examined on foliage of soybean, Glycine max (L.) Merrill, versus deer pea, Vigna luteola (Jacq.) Benth, a wild host plant of A. gemmatalis. AgNPV sprayed on upper leaf surfaces lost ≥60% of its activity within 2 d, whereas the virus sprayed on the underside of foliage lost ≤13% in the same time period, regardless of host plant. The results of the soil and water persistence experiments indicate that classical biological control of A. gemmatalis with AgNPV is less likely to succeed in wild, coastal legumes than in the soybean agroecosystem.

Sugar-Feeding Strategy of Adult Velvetbean Caterpillar (Lepidoptera: Noctuidae)

Although nectar availability has long been recognized as the major cause of outbreaks of some important lepidopteran pests, basic knowledge on nectar feeding by adults of any single noctuid species is very limited. Understanding of adult feeding behavior also is essential to the development of adult control technology for these pests. This study measured sucrose consumption, using a gravimetric method, and investigated related sugar feeding behavior of adult velvetbean caterpillar, Anticarsia gemmatalis Hubner. Adult females reared in field cages on soybean foliage consumed 3 times as much sucrose solution as females reared in the laboratory on artificial diet. Glucose, fructose, and sucrose were all equally acceptable to velvetbean caterpillar moths. Various concentrations of sucrose solution (1–40%) also were equally acceptable to the moths. However, much greater volumes of sucrose solution were consumed by female moths at lower concentrations than at higher concentrations. When fed with low concentrations (<20%), the moths regurgitated large volumes of excess water through their proboscis. Surprisingly, there was no sugar in the regurgitant although regurgitation occurred soon after or during the process of feeding. When provided with both 30% (wt:vol) sucrose solution and distilled water, lifetime total liquid consumptions by field-reared females and males were 849.3 ± 104.0 (mean ± SE) μ l and 964.0 ± 60.0 μ l, respectively, with no significant differences in consumption between sexes. Both sexes fed heavily in the initial 2 d of their adult lives with the peak consumption on the 1st day after emergence.

Bacterial Streak and Bulb Rot of Sweet Onion: II. Epiphytic Survival of Pseudomonas viridiflava in Association with Multiple Weed Hosts.

A semiselective agar medium (T-5) was used to sample environment and plant material as a habitat for Pseudomonas viridiflava. Soil, irrigation water, soybean foliage, and foliage from various weeds in an onion-growing area were assayed over a 5-year period. P. viridiflava was recovered only as an epiphytic resident from weed species that included cutleaf evening primrose, dandelion, common fumitory, purple cudweed, spiny sowthistle, Virginia pepperweed, and wild radish. The bacterium apparently overseasons in association with these weeds, because its presence was detected prior to, as well as during, the onion-growing season. Preliminary tests indicated that weed control may suppress bacterial streak and bulb rot levels.

Residual Toxicity of Selected Insecticides to Heteropteran Predaceous Species (Heteroptera: Lygaeidae, Nabidae, Pentatomidae) on Soybean

Residual toxicity of selected insecticides to the heteropteran predators Geocoris punctipes (Say) adults, Nabis roseipennis Reuter adults, and Podisus maculiuentris (Say) nymphs and adults, was evaluated by exposing predators to soybean foliage (treated in the field) in petri dishes. Toxicity of chlorfenapyr residues on soybean foliage was greater than that of the standard insecticide, permethrin, and another new compound, emamectin benzoate, to all 3 predaceous species. Methyl parathion-treated foliage was significantly more toxic to G. punctipes than were the remaining insecticides, except chlorfenapyr, 6 h after application; however, by 24 h after application, percentage mortality of G. punctipes declined from 100 to 11.7% following exposure to methyl parathion residues. Duration of chlorfenapyr residues was evident up to 72 h after application, and chlorfenapyr-treated foliage was significantly more toxic to G. punctipes than all other insecticides 24 to 72 h after application. Insect predators are highly mobile and spend considerable time searching for prey species on agronomic plants. Thus, insecticides with persistent foliar residues generally discriminate against predaceous species as they search for prey species or when they recolonize fields previously treated with insecticides.

Survival and Development of Gypsy Moths (Lepidoptera: Lymantriidae) on Corn and Soybean Foliage

The availability of suitable hosts is a major factor influencing insect migration. We examined gypsy moth, Lymantria dispar L., feeding and development on corn, Zea mays L., and soybeans, Glycine max Merr., plants widely available in midwestern states, to determine their potential to influence patterns of gypsy moth migration and establishment outside of the northeastern forests. Although corn did not seem to be a suitable host for gypsy moth larvae, soybean leaves were acceptable, and ≈50% of the larvae reared on soybean leaves developed to the adult stage. The extent of foliar feeding and the level of larval developmental perfor-mance differed significantly among 4 soybean cultivars evaluated, indicating a wide range of suitability to gypsy moth herbivory. Previously demonstrated resistance to Mexican bean beetle, Epilachna varivestis Mulsant, in soybean lines correlated well with resistance to gypsy moth herbivory. Gypsy moth survival and development to fertile adults on soybean leaves is a new finding that is not likely to have immediate economic impact but could have dispersal significance if soybeans prove to be a suitable alternate host.

Host-finding by cabbage looper moths (Lepidoptera: Noctuidae): Learning of host odor upon contact with host foliage

Mated female cabbage looper months that were caged with cotton, celery, or soybean foliage were attracted significantly more often than inexperienced moths to the odor of the same species of plant the following night. Moths that were caged with cotton or celery foliage were attracted significantly more often the following night only to the foliage of the same species, and not to the foliage of the other plant species. Brief contact by a moth or a single oviposition on plant foliage was sufficient to increase subsequent attraction to plant foliage. This behavior appears to be associative learning of host odor.

Gravimetric Method for the Measurement of Sugar Consumption by Adult Velvetbean Caterpillar (Lepidoptera: Noctuidae)

Determination of food consumption by adult Lepidoptera, especially noctuid species, has not been well studied, possibly because of a lack of appropriate methodology. In order to measure sugar consumption by velvetbean caterpillar, Anticarsia gemmatalis Hubner, a gravimetric method was developed and is presented here together with results obtained using this method. After 24-h exposure to a moth, liquid consumption by the moth was determined by weighing the remaining solution on an electronic balance. The amount of solution consumed was calculated by converting the difference between the weight of the remaining solution and that of the unfed control to a volumetric value. Velvetbean caterpillar moths consumed a significantly greater volume of solution at lower sugar concentrations than at higher concentrations. Female moths from larvae reared on soybean foliage in field cages consumed three times that of moths from larvae reared on artificial diet in the laboratory. This method was simple, accurate, and required minimum handling of test insects. It was suitable for the measurement of food consumption of velvetbean caterpillar moths and could also be suitable for other lepidopteran species.

Timing of Food Plant Availability: Effect on Survival and Oviposition of the Bean Leaf Beetle (Coleoptera: Chrysomelidae)

The objective of these experiments was to estimate the effects of large-scale adoption of delayed soybean planting on population dynamics of the bean leaf beetle, Cerotoma trifurcata (Forster), in the Midwest. If growers throughout a region (e.g., thousands of contiguous hectares) planted soybean at the end of the optimal planting period (i.e., late May), beetles would be forced to remain on alternate food plants until soybean emerged. To simulate this consequence of delayed soybean planting, overwintered adult C. trifurcata were caged on foliage of selected plant species for 5–28 d. Plants tested were alfalfa (‘Blazer’ and ‘Vernal’), oats (‘Starter’), wheat (‘Guard’), maize (‘Garst 8532’ and ‘Henze 6338’), and soybean (‘Corsoy 79’) as a control. Beetles that survived were transferred to soybean (‘Corsoy 79’) foliage for the remainder of their lives. In all treatments, female lifespans and oviposition rates were reduced significantly relative to the soybean control. Females caged on grasses had significantly shorter lifespans and lower oviposition rates than those caged on alfalfa. Lifespan and oviposition declined in proportion to number of days without soybean. Survivors from alfalfa regained relatively high oviposition rates once transferred to soybean. In contrast, beetles caged on grasses for 14 d or longer never oviposited even after being transferred to soybean. Results suggest that large-scale adoption of delayed soybean planting would reduce beetle survival and reproduction, with the magnitude of reductions being greatest in regions without alfalfa.

Populations of Foliage‐Inhabiting Arthropods on Soybean with Reduced Tillage and Herbicide Use

AbstractModification of tillage and herbicide use patterns to reduce adverse environmental effects on soybean [Glycine max (L.) Merr.] production may impact arthropod populations and damage in soybean. The objectives of this field study were to examine the effect of reduced tillage and herbicide use on populations of foliage‐inhabiting phytophagous and beneficial arthropods and their damage in soybean. Tillage treatments of no‐tillage, chisel‐plow with disking, and moldboard plow with disking and herbicide regimes of high (preplant and postemergence control), reduced (postemergence control), and no herbicide use were established in a 2‐yr rotation of corn (Zea mays L.), winter wheat (Triticum aestivum L.), and soybean. Phytophagous and predatory arthropods were sampled from soybean foliage with the shake‐cloth technique throughout the season in 1988, 1990, and 1992. Tillage treatments did not consistently affect any arthropod groups except stink bugs (Pentatomidae), which were more abundant in no‐tillage than plow‐tillage treatments, and bigeyed bugs (Geocoris spp.), which were more abundant in both plow‐tillage treatments than in no‐tillage. Herbicide regime also had no consistent effect on abundance of any taxa. Additionally, tillage and herbicide regimes had little consistent effect on soybean lepidopteran defoliation and pod damage caused by the bean leaf beetle [Cerotoma trifurcata (Forster)] over the 3 yr. There were extensive stand losses due to rodent damage (cotton rat; Sigmodon hispidis Say &amp; Ord) in the no‐tillage, no‐herbicide system in 1992, where crabgrass [Digitaria sanguinalis (L.) Scop.] was prevalent. These results suggest that tillage and herbicide use practices can be modified without greatly affecting arthropod populations and their damage in soybean. However, these results imply that the potential for managing arthropod populations by modified tillage and herbicide use is limited in soybean.

Experimental method to measure gaseous uptake of 14C-toluene by foliage

An experimental method is described to measure foliar uptake and translocation of volatile organic compounds in plants. A flow-through exposure chamber was designed to determine phytoxicity of volatile organic compounds; an air-tight chamber was used for exposure of whole plants to radiolabeled test compound. 14C-toluene uptake by soybean ( Glycine max) foliage was measured as an example of the experimental approach. Leaf tissue concentrations of 14C-toluene were measured over a 55.5-hr exposure period during light and dark periods. Photosynthetic rate was not affected by chronic atmospheric exposure to 27 μmole cm −3 hr toluene. During a 55.5-hr exposure to 7.2 μmoles cm −3 hr 14C-toluene (1.94 Bq cm −3), deposition velocities were greatest in the light phases and showed a marked decrease during the dark phases of exposure, suggesting that stomatal uptake as well as surface deposition contributed to toluene uptake. 14C was translocated from foliage to the roots. These data indicate that deposition of volatile organic compounds to vegetation may constitute a mechanism leading to herbivore exposure to volatile hazardous organics at waste sites. The experimental method described can be used to measure foliar uptake and translocation of volatile organic compounds to whole plants under laboratory conditions.

Oxidative responses in soybean foliage to herbivory by bean leaf beetle and three-cornered alfalfa hopper

Variation in induced responses in soybean is shown to be dependent, in part, upon herbivore species. Herbivory by the phloem-feeding three-cornered alfalfa hopper caused increases in the activities of several oxidative enzymes including lipoxygenases, peroxidases, ascorbate oxidase, and polyphenol oxidase. Bean leaf beetle defoliation caused increased lipoxygenase activity, but had little effect upon peroxidase, polyphenol oxidase, ascorbate oxidase, or trypsin inhibitor levels in either field or greenhouse studies. In one field experiment, prior herbivory by the bean leaf beetle subsequently reduced the suitability of foliage to the corn earwormHelicoverpa zea. The contribution of these findings to emerging theories of insect-plant interactions is discussed.

Metabolic pathways and residue levels of thifensulfuron methyl in soybeans

Radiolabeled thifensulfuron methyl [methyl 3-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl]amino]sulfonyl]-2-thiophenecarboxylate], the active ingredient in Pinnacle herbicide, was applied postemergence to greenhouse-grown soybean seedlings at 8 and 16 g of active ingredient/ha (2-4 times the labeled use rate), with and without surfactant. The soybeans were grown to maturity, and the metabolic pathways and total radiolabeled residue levels were determined. The concentration of thifensulfuron methyl in soybean foliage declined with half-lives ranging from 5 to 20 days to approximately 8 ppb 30 days after treatment. The identities and concentrations of surface residues and metabolites in soybean foliage were quantitated at 0, 7, and 30 days after treatment. Radiolabeled residues in mature soybean seeds produced from these elevated application rates were extremely low and ranged from 0.4 to 1.6 ppb.

Influence of Diet on the Density-Dependent Phase Polymorphism of Velvetbean Caterpillars (Lepidoptera: Noctuidae)

Velvetbean caterpillars, Anticarsia gemmatalis Hubner, were reared at different larval densities on meridic diets containing different amounts of foliage. The degree of dark body color and yellow to orange head color was highest in larvae reared crowded and on meridic diets containing the most dried soybean foliage in artificial diet or consisting completely of fresh kudzu or soybean foliage. No body color change from green was observed in solitary larvae reared on the same diets as crowded larvae. Larvae developed most rapidly on meridic diets containing the lowest and highest amounts of foliage. On all meridic diets tested, solitary larvae developed to the pupal stage at least 1 d faster than crowded larvae. Larvae reared on fresh foliage developed into pupae and adults that weighed the least.

Diet Influences on Permethrin Susceptibility and Growth of Soybean Looper Larvae (Lepidoptera: Noctuidae)

Larvae from several strains of soybean looper, Pseudoplusia includens (Walker), were reared on artificial diet, soybean foliage, and cotton foliage and tested for susceptibility to permethrin. Larvae from all three strains were significantly less susceptible to permethrin when reared on cotton than when reared on artificial diet. There were no significant differences in LD50s between soybean and artificial diet-reared larvae for any of the strains. Larvae from a permethrin-selected laboratory strain were 2-fold less susceptible when reared on cotton than on soybean; no significant difference in LD50 between soybean and cotton-reared larvae occurred for the other strains. Three soybean looper strains also were reared on soybean and cotton to compare development of soybean looper on these hosts. The development time of all three strains from eclosion to pupation was significantly longer when reared on cotton than on soybean, and all larval stadia except the second and third ins tars lasted significantly longer. Larvae and pupae tended to be heavier when reared on cotton, and there was no evidence of lower survival rates or increased incidence of supernumerary stadia when soybean looper developed on cotton, indicating that cotton is a suitable host for the insect.

Feeding Activity and Mortality of Permethrin-Resistant and Susceptible Soybean Looper (Lepidoptera: Noctuidae) Larvae on Soybean Foliage Treated with Insecticide

Third and fifth instar soybean loopers, Pseudoplusia includens (Walker), from three field strains resistant to permethrin and a susceptible laboratory strain were exposed individually to untreated soybean leaflets or leaflets treated with field rates of permethrin, thiodicarb, and Bacillus thuringiensis Berliner (var. kurstaki ). Leaf area was measured before a larva was placed on a leaflet. Leaf area and mortality were measured 24, 48, and 72 h after a larva was exposed to treated and untreated foliage. Mortality of permethrin-resistant larvae on foliage treated with permethrin was significantly lower than that observed for susceptible larvae. Thiodicarb and B. thuringiensis were equally effective against permethrin-resistant and susceptible larvae after 72 h, but mortality was delayed with resistant larvae. All insecticide treatments significantly reduced leaf area consumption by both permethrin-resistant and susceptible larvae regardless of instar, compared with consumption when they fed on untreated foliage. However, permethrin-resistant third and fifth instars consumed significantly more foliage treated with permethrin compared with any other larvae on treated foliage in most experiments. Reductions in consumption by resistant larvae on foliage treated with permethrin ranged from 42 to 68% and 55 to 76% for third and fifth instars, respectively, compared with consumption on untreated foliage.

Changes in insecticide efficacy against Helicoverpa zea (Boddie) on soybean due to larval size and plant phenology

The within-plant distribution of corn earworm, Helicoverpa zea (Boddie), on soybean, Glycine max (L.) Merrill, changes with larval size and plant phenological stage. Small (instars 1 and 2) larvae on H. zea are often found within rolled leaves and flowers when each plant part is available (vegetative and flowering stages). Medium (instars 3 and 4) and large (instars 5 and 6) larvae at all plant reproductive growth stages, and small larvae when rolled leaves and flowers are not available, are found primarily on open leaves. Because both rolled leaves and flowers may protect small larvae from exposure, insecticide efficacy may be reduced in soybean fields during the vegetative or flowering stages. To ensure that any differences observed in field experiments were not due to differences in susceptibility, the relative mortality of small, medium, and large H. zea larvae fed on soybean foliage treated with insecticides was assessed in the laboratory. No significant difference between small, and medium plus large larvae (combined) was detected in one test, but mortality of small larvae was significantly higher in another test. In the field, the number of H. zea larvae on insecticide-treated and untreated soybeans was compared 1 and 7 days after application, with separate experimental designs. The relative number of small, medium, and large larvae in each treatment varied with soybean growth stage. Differences between insecticide treatments were greater for large larvae than for small larvae when soybeans were flowering. When soybeans were in the pod-forming stages, few larvae of any size were found in the insecticide-treated plots one day after application. One week after application, greater differences in larval numbers were observed for small and medium larvae on soybeans in early reproductive growth stages than for large larvae in early stages or all sizes in later stages. It was concluded that insecticide efficacy for small H. zea larvae is low on soybeans in vegetative or early flowering growth stages. Because mortality of small larvae was higher at later plant growth stages, and as mortality of small larvae fed on insecticide-treated foliage was as high as, or higher than, mortality of larger larvae, the low efficacy may be attributed to lower exposure to insecticides.

Effect of Constitutive and Herbivore-induced Extractables from Susceptible and Resistant Soybean Foliage on Nonpest and Pest Noctuid Caterpillars

Soybean foliage from susceptible (‘Bragg’) and resistant (PI 229358 and D75-10169) lines was extracted in several nonpolar and polar organic solvents to assess constitutive (mite-free) and induced (mite-damaged) activity against nonpest and pest noctuid caterpillars. The benzene fraction, incorporated in artificial diet, contained most of the constitutive activity of both the resistant and susceptible lines, as indicated by reduced relative growth rate (RGR) of velvetbean caterpillar, Anticarsia gemmatalis Hubner; corn earworm, Helicoverpa (=Heliothis) zea (Boddie); tobacco budworm, H. vlrescens (F.); and fall armyworm, Spodoptera frugiperda (J. E. Smith) compared with larvae fed the extract- and solvent-free control diet. Induced activity from mite-damaged greenhouse-grown plants and A. gemmatali s- damaged field-grown plants was detected primarily in the petroleum ether fraction. Among the species tested on the induced fractions (A. gemma talis, S. frugiperda , and the cabbage looper, Trichoplusia ni (Hubner)), S. frugiperda was the most sensitive species, as demonstrated by reduced RGR. Overall, among the species (H. zea, H. virescens , and T. nil more tolerant of the soybean foliage fractions, only H. zea is a major soybean foliage pest. Surprisingly, among the two most sensitive species, A. gemmatalis is a legume specialist and major soybean pest, whereas S. frugiperda is a polyphagous species but not a soybean pest. These results suggest that presumed soybean-adapted species may not be more resistant than soybean-naive ∼pecies to the deleterious effects of soybean foliage extracts.

Measuring Herbicide Injury to Soybeans (Glycine max) Using a Radiometer

Light reflectance from soybean foliage was compared to visual evaluations for assessing soybean injury caused by postemergence-applied paraquat and glyphosate. Coefficients of variation and of determination from multiple linear regressions for both herbicides indicated that reflectance was better correlated with injury measured by changes in leaf number, leaf weight, and stem weight than visual evaluations. Correlation coefficients among radiometer readings taken by different individuals were ≥0.98 for both herbicides. Correlation coefficients among visual evaluators ranged from 0.69 to 0.96 and from 0.74 to 0.94 for plots treated with paraquat and glyphosate, respectively. Light reflectance measured with a radiometer may be useful in evaluating injury from herbicides that cause chlorosis, necrosis, or defoliation of the target species.

Insect responses to plant water deficits. I. Effect of water deficits in soybean plants on the feeding preference of Mexican bean beetle larvae

Abstract. 1. We examined the preference of larvae of the Mexican bean beetle, Epilachna varivestis Mulsant (Coleoptera: Coccinellidae), for foliage of soybean (Glycine max [L.] Merr.) grown under several levels of water deficit. Third instar larvae were exposed simultaneously to excised foliage from plants that were either well‐watered (control) or had experienced water deficits (treatment).2. Water‐deficient plants were re‐watered 12 h prior to initiating feeding trials to eliminate physical differences between control and treatment foliage such as leaf water potential, diffusive resistance, relative water content, and foliage toughness.3. Examination of the free amino acid contents of re‐watered and excised foliage indicated that amino acid concentrations increased markedly in foliage grown under water deficits, and that this increase persisted during the preference tests.4. Larvae preferred control foliage, but shifted preference to treatment foliage under mild water deficits. When the leaf water potential of water‐deficient treatment foliage was lower than – 1.13 MPa or when it was more than 0.5 MPa lower than that of control foliage, larvae preferred to feed on foliage from well‐watered control plants.5. The expression of preference for well‐watered control foliage was coincident with increases in the concentrations of total free amino acids and individual free amino acids in the water‐deficient treatment foliage.6. These results are inconsistent with White's (1974) hypothesis because Mexican bean beetle larvae avoid plants grown under water deficits that have increased concentrations of free amino acids.

Investigation of Trace Metal Concentrations in Crops and Soils Near a Fossil-fuel Power Plant in Maryland

The objectives of this study were to compare changes in atmospheric deposition rates for water soluble Zn, Cu and Mn associated with a doubling of the generating capacity of a fossilfuel power plant located in southern Maryland with concentrations of extractable metals in soils and In corn and soybean foliage. Three atmospheric deposition samples were collected monthly during each summer from 12 research and monitoring sites located 1.6, 4.8 and 9.6 km distances from the Chalk Point Generating Station for two years before and after the June 1975 expansion of generation capacity from 660 to 1320 MW. Crop leaf samples were collected at flowering, and 0-15 cm depth soil samples were collected from research plots each May. Averaged over monitoring sites and plant operational periods, respectively, significant decreases were found in atmospheric deposition rates for Zn and Mn from pre- to post-plant expansion and with increased distances. The Cu deposition rates remained unchanged from pre- to post-expansion; ...