Progress 05/01/02 to 04/30/05
Outputs
Bt transgenic sweet corn was compared to non-Bt sweet corn in randomized, replicated trials in 2005. When no treatment was made to the non-Bt sweet corn, 100 percent of the ears had damage. Damaged to ears by both corn earworm (CEW) and fall armyworm (FAW) was about 40 percent less when only Bt sweet corn was compared with sweet corn without the Bt transformation. However, the use of Bt transformed sweet corn alone was not sufficient to prevent heavy damage (more than 60 percent of ears with damage). When neem (applied at 8 oz/ac) or Spintor was used, damaged was further reduced to around 20 percent. All other treatments had more than 40 percent damaged ears. In general, the Spintor treated plots had less than 1 percent CEW larva per 100 ears sampled compared to other treatments where over 10 percent of the ears that were infested by CEW larvae. Populations of FAW larvae were low this year and no larvae were found in the Spintor-treated plots. Pheromone traps for the
FAW and CEW revealed that there were three major peaks of about 20 CEW moths per trap per night. These occurred at 8 day intervals on July 10, 18 and 26. Populations of FAW in pheromone traps averaged only one or two per trap. The efficacy of several currently registered Bt products (DiPel, Xentari, CryMax) and one unregistered Bt material V-10156) were assessed and compared to recommended chemical pesticides for management of lepidopterous pests in collard. Although spinosad and emamectin benzoate were significantly more efficacious than the Bt materials, the efficacy of all Bt materials was statistically equivalent to the other chemical pesticides and there were significantly fewer larvae in the Bt plots than in the untreated controls. In spite of the greater efficacy of some of the chemical pesticides, crop quality was sufficient for market in the Bt-treated plots
Impacts
Increased per capita consumption of vegetables (15 percent yearly) during the last 15 years is partly due to the rise of public awareness of health benefits from eating vegetables. However the health of the vegetable industry nationwide is at risk, primarily from pest-control related issues. Blemishes or defects influence consumers. To produce low-defect, high consumer appeal products, the industry relies upon routine and excessive applications of pesticides to control disease and insect pests. Market pressures lead to vegetables receiving more pesticides than any other crop grown. Over 240 million pounds of pesticides, costing over $480 million annually, are used in the Southeast alone to control vegetable pests. Alternative pest controls are being investigated, creating benefits for the grower and reducing public health concerns about food safety. Reducing pesticide use reduces production costs, pesticide residues, runoff into water supplies and effects on non-target
and beneficial insects and microbes. In Lexington County, SC, research on Brassica (collards, cabbage, etc.) crop acreage has yielded promising results. The use of chemical pesticides has decreased from 14 applications of synthetic chemical insecticides to five or six applications of biological control materials. This model of alternative pest control is being refined and extended to other vegetable and specialty crops. Organic farmers likely will be early adopters of research results from this project.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Following preliminary screening experiments of cowpea germplasm in the USVL breeding project, six accessions were selected for further evaluation as a weed suppressing cover crop. The selections exhibit rapid early growth, are indeterminate, and short day flowering. These characteristics allow them to rapidly overgrow annual weeds early in the growing season and remain vegetative, maintaining weed suppression throughout the summer. Steam distillates of noni fruit (Morinda citrafolia) proved to be highly inhibitory to proso millet (Panicum miliaceum) seed germination and growth of four pathogenic fungi (Fusarium oxysporum, F. solani, Lasiodiplodia theobromea, Rhizopus stolonifer) in bioassay experiments. This indicates that the fruit may contain components with useful biological activities. Extract of spider plant (Cleome gynandra) and tansy (Tanacetum parthenium) were prepared and incorporated into the diet of the beet armyworm. At a 5% concentration, both plant
extracts caused over 90% mortality. Sweet corn, containing the gene that codes for the Bacillus thuringiensis toxin, was tested in field plots along with Spintor, fall armyworm (FAW) nucleopolyhedrovirus, and the corn earworm (CEW) nucleopolyhedro virus. Sweet corn containing the Bt gene were significantly less susceptible to attack by both of these key pests. However, under heavy insect pressure, the Bt-transgenic sweet corn was attacked at levels that were considered unmarketable. Field plots with the Spintor and Spintor Plus FAW virus were the only ones with marketable ears. Field tests will continue to try to identify non-chemical materials that provide acceptable control of these pests. Control programs for the southern green stink bug (SGSB), Nezara viridula, routinely include application of broad spectrum chemicals. Few studies have focused on the effects of neem on predators. In order to test the effects of neem against predators of eggs of the SGSB, colonies of the pest were
established in the laboratory. Egg masses were treated with 1 ml of a 0.5% solution onto each egg mass. Water treated egg masses served as controls. Eggs were then placed in the field. A companion test was carried out whereby eggs were placed in the field and then the field plots were treated. Controls were left untreated. Eggs were examined twice per day and any predator found feeding on the eggs was recorded. After 7 days, eggs were collected and counted. Results showed that there was no difference in predation of the neem-treated or water-treated egg masses. Likewise, there were no differences in egg predation from neem-treated plots compared to that in untreated plots. In laboratory tests with the diamondback moth virus, PxMNPV, we found that the potency of this microbial agent was increased by adding certain florescent brighteners, including Blankophor P167, at a concentration of 1%. Other brighteners, however, reduced the activity of the PxMNPV. In addition, Blankophor HRS at 1%
enhanced the necleopolyhedrovirus of the celery looper (AfMNPV) against DBM. Similar results were found in the corn earworm and beet armyworm, which are both susceptible to PxMNPV and AfMNPV.
Impacts
Results from these studies provide information for making better pest maangement decisions. This is based on a broader understanding of the mechanisms involved in the interaction between biological control agents and other alternatives to chemical pesticides and the environment. As these mechanisms are illucidated, it is expected that numbers of pesticide applications and expense to the grower will continue to decrease and environmental quality will be greatly improved.
Publications
- No publications reported this period
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Progress 01/01/03 to 12/31/03
Outputs
Studies were conducted to understand the relationship between ascoviruses, their lepidopteran hosts and their parasitoids. Noctuid larvae were collected from cotton, soybean and corn in South Carolina during the summer of 2003. Noctuid larvae that were commonly found in cotton were Heliothis virescens, Helicoverpa zea, Spodoptera exigua, and Pseudoplusia includens, and in soybean were Anticarsia gemmatalis, Plathypena scabra, P. includens and H. zea. Ascovirus infections were recorded from S. exigua, H. zea, H.virescens, P. includens, and S. frugiperda. Cotesia marginiventris and Microplites croceipes populations were relatively high when ascovirus infections were observed in S. exigua and H. zea. There was a correlation between ascovirus infection and parasitoid populations. Thus, although the exact mode of transmission of the entomopathogen is not know, it is likely that the parasitoids are spreading the disease by their oviposition activity. A new isolate of a
Plutella xylostella nucleopolyhedrovirus (PxNPV) was found in the larvae of the diamondback moth. In collaboration with the Insect Biocontrol Laboratory in Beltsville, MD, the insect virus was increased in laboratory colonies of beet armyworm and a small field test was carried out in collard in Charleston, SC. The PxNPV plus the optical brightener, Blankaphor, was applied weekly from May 16 until June 13, 2003. Although the PxNPV treatment was not as good as the commercial insecticide Spintor, there was a significant reduction in numbers of diamondback moth larvae compared to the untreated control plots. Biological, chemical, and combinations of biological and chemical seed treatments were tested on snap bean. Disease pressure was high, with a mean stand of only 46 percent, due primarily to damping-off caused by Pythium. The number of plants remaining 28 days after seeding was greater with Captan plus streptomycin than in the untreated control. The systemic-acquired resistance
products Actigard and Messenger; the biofungicides Serenade, Sonata, and Milsana; and the reduced risk contact fungicide Oxidate were tested in combination or alternation with chlorothalonil to see if growers could reduce the amount of chlorothalonil used. Oxidate and Messenger were applied in combination with a reduced rate of chlorothalonil and the other four reduced-risk fungicides were applied in alternation with the full rate of chlorothalonil. Chlorothalonil applied alone at two rates was included as the controls. Downy mildew was the only disease present in these plots. All treatments reduced downy mildew compared with the nonsprayed control. All sprayed treatments increased weight of marketable fruit compared with the nonsprayed control. All sprayed treatments also increased fruit sugar contents compared with the unsprayed control.
Impacts
Results from these studies provide information for making better pest maangement decisions. This is based on a broader understanding of the mechanisms involved in the interaction between biological control agents and other alternatives to chemical pesticides and the environment. As these mechanisms are illucidated, it is expected that numbers of pesticide applications and expense to the grower will continue to decrease and environmental quality will be greatly improved.
Publications
- Abudulai, M., B. M. Shepard and P. L. Mitchell. 2003. Antifeedant and toxic effects of a Neem (Azadirachta indica A. Juss) based formulation Neemix against Nezara viridula (L.) (Hemiptera: Pentatomidae). Journal of Entomological Science. 38: 398-408.
- Keinath, A. P., and DuBose, V. B. 2003. Evaluation of fungicides for prevention and management of powdery mildew on watermelon. Crop Prot. 23:35-42.
- Keinath, A. P., Harrison, H. F., Marino, P. C., Jackson, D. M., and Pullaro, T. C. 2003. Increase in populations of Rhizoctonia solani and wirestem of collard with velvet bean cover crop mulch. Plant Dis. 86:719-725.
- Abudulai, M., B. M. Shepard and A. B. Salifu. 2003. Field evaluation of a neem (Azadrachta indica A. Juss)-based formulation Neemix against Nezara viridula (L.) Himiptera: Pentatomidae) in cowpea. International Journal of Pest Management. 49: 109-113.
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Progress 01/01/02 to 12/31/02
Outputs
Cotton aphid populations and the aphid pathogen, Neozygites fresenii, were monitored in Bt cotton to determine the impact of new insect management practices on the development of fungal epizootics in aphid populations. Data show that the new management practices in Bt cotton provide an ideal environment for the fungus to operate and reduce aphid populations. Fungal pathogens were monitored in lepidopterous pests of soybeans. Nomuraea rileyi infected all five species sampled (green cloverworm, velvetbean caterpillar, soybean looper, corn earworm, and beet armyworm). Two distinct periods of infection were noted (late July and late August-Sept.). This provides evidence that two distinct strains are operating in the same fields. Host range studies with these strains appear to confirm this hypothesis. A fungal pathogen of grasshoppers that we collected from Indonesia was identified by Richard Humber as Paecilomyces reniformis. However, our molecular characterization
studies indicate that it may be more closely related to Nomuraea than to Paecilomyces. The incidence of ascoviruses were moitored in lepidopterous pests of cotton. Infection by these viruses appeared correlated with higher populations of the parasitoid, Cotesia marginiventris. Biological, chemical, and combinations of biological and chemical seed treatments were tested on snap bean. Although disease pressure was low, Bacillus sp. strain 3086 in combination with Captan and streptomycin improved stands over the nontreated control. A field experiment was done with cabbage and broccoli to evaluate shallow planting depth as a cultural control for wirestem. With both crops, wirestem was as low with shallow planting as in the non-infested control. Plants set shallowly did not lodge more frequently than plants set deeply, despite above average rainfall during the experiment. Six bio-fungicides and reduced-risk fungicides rotated with chlorothalonil reduced downy mildew on muskmelon, although
rotated treatments were not more effective than chlorothalonil applied alone biweekly. All sprayed treatments increased yield and sugar content of fruit compared with the non-sprayed control except Actigard alternated with chlorothalonil.
Impacts
Management of insect pests in Bt-transformed plants requires a different strategy. Bt-transformed cotton provides an ideal environment for naturally-occurring insect predators, parasites and pathogens to work because of reduction of chemical pesticides. This information should be essential for field scouts or farmers who make chemical treatment decisions. Shallow planting appears to be effective as a non-chemical alternative to fungicide applications to control wirestem on broccoli and cabbage.
Publications
- Keinath, A.P. 2002. Survival of Didymella bryoniae in buried watermelon vines in South Carolina. Plant Disease 38:32-38.
- Keinath, A.P., DuBose, V.B., May, W.H. III, and Cantrell, J.P. 2002. Effect of crop rotation and cultivar on gummy stem blight epidemics in watermelon. Biol. Cult. Tests 17:V25.
- Keinath, A.P. and Harrison, H.F. 2002. Increase in populations of Rhizoctonia solani and wirestem of collard after a velvetbean cover crop. Phytopathology 92:S150.
- Hagiwara, Kyoji, Shujing Rao, Simon Scott, and Gerald Carner. 2002. nucleotide sequences of segments 1, 3, and 4 of the genome of Bombyx mori cypovirus 1 encoding putative capsid proteins VP1, VP3, and VP4, respectively. J. Gen. Virol. 83:1477-1482.
- Rao S, G. R. Carner, S. W. Scott , T. Omura, and K.Hagiwara. 2003. Comparison of the amino acid sequences of RNA-dependent RNA polymerases of cypoviruses in the family Reoviridae. Arch. Virol. 148: 209-219.
- Dufault, R. J., J. W. Rushing, R. L. Hassell, B. M. Shepard and G. McCutcheon. 2002. Influence of cultural system and fertility on feverfew biomass and marker compound content. HortScience. 37: 188.
- Dufault, R. J., J. W. Rushing, R. L. Hassell, B. M. Shepard, and G. McCutcheon. 2002. Influence of fertility on the growth and marker compound of field-gown Echinacea species and feverfew. Scientia Horticulturae. 1890: 1-9.
- Abudulai, M., and B. M. Shepard. 2002. Effects of Neem (Azadirachta indica A. Juss) on Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae), a Parasitoid of Nezara viridula (L.) (Hemiptera: Pentatomidae). Journal of Entomological Science (Accepted for Publication).
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