Four bacterial strains show promise as biological controls for take-all, a fungal disease of wheat. ARS scientists and cooperators at Virginia Polytechnic Institute and State University screened large numbers of diverse bacteria present around wheat roots for their ability to suppress the fungus Gaeumannomyuces graminis var. tritici (Ggt), which causes take-all. This disease demolishes wheat harvests around the world, causing wheat roots to turn black and die, reducing yields by 50 percent or more, and costing U.S. wheat growers alone millions of dollars in years with severe infestations. The four bacterial strains that show potential as biocontrol agents will be tested separately and in combination with commonly used wheat pesticides in field trials next year.

Biocontrol of Plant Diseases Laboratory, Beltsville, MD
Daniel Roberts, (301) 504-5680, droberts@asrr.arsusda.gov

One of the mechanisms behind tobacco budworm's growing resistance to Bacillus thuringiensis (Bt) toxin may have been uncovered by an ARS scientist. Bt toxin causes the insect's mature gut cells to swell, burst, and die. Using tobacco budworm midgut cells cultured in the laboratory, the scientist found many of the cultured gut cells were killed by the toxin. But some cells responded to the injury by producing cytokines, substances that signal gut stem cells to multiply and rapidly produce new mature gut cells. When the Bt toxin was washed from the cultured gut cells, the new healthy cells quickly replaced the dying ones. This suggests that if the dose of Bt is insufficient or if the insect has developed a way to more rapidly replace its destroyed gut cells, the insect's midgut will heal and function normally. This could explain why low doses of Bt toxin don't kill insects.

Insect Biocontrol Laboratory, Beltsville, MD
Marcia Loeb, (301) 504-8103, mloeb@asrr.arsusda.gov

U.S. corn farmers now have three new products to choose from to control adult corn rootworms. The products have been evaluated by ARS researchers in several national areawide integrated pest management (IPM) projects, as part of USDA's commitment to reduce reliance on agricultural chemicals. Rootworms drive up the cost of farming in the Corn Belt and Texas, which ranks seventh in corn production. ARS researchers in Texas showed that with proper timing and application methods, these three new products can cut corn rootworm damage while having little or no harmful effect on the environment. The first product evaluated was Slam, made by MicroFlo, Inc., of Lakeland, FL. Slam was based on ARS research in Brookings, SD. The second product was CideTrak, developed under a cooperative research and development agreement between ARS and Trece Inc., in Salinas, CA. CideTrak uses an insect-feeding stimulant and low-dose toxicants. The third product, Invite, marketed by FFP AgroTech., Inc., Eustis, FL, includes Hawksberry watermelon-juice feeding stimulant concocted by ARS researchers in Beltsville, MD. Both Invite and CideTrak allow farmers to use just one-tenth of the allowed rate of toxicant for pests in corn. ARS' areawide IPM projects, which began in 1994, also include control of codling moths, leafy spurge, and stored-grain insects.

Areawide Pest Management Research, College Station, TX
Clint Hoffmann, (979) 260-9521, choffmann@tamu.edu

A new bioherbicide shows promise as an alternative to methyl bromide for controlling weeds in tomatoes. Discovered by ARS scientists, the bioherbicide, Myrothecium verrucaria, comes from the sicklepod plant found primarily in the southeastern United States. M. verrucaria controls common purslane, horse purslane, ground spurge, and spotted spurge—all serious weed pests in commercially grown tomatoes. Tomatoes account for the highest consumption of methyl bromide (23 percent) of all crops. About 3,773 tons are applied annually to tomatoes to control nematodes (tiny worms), insects, and weeds. ARS researchers treated plots with natural infestations of these weeds with Myrothecium before planting Beefsteak tomato seedlings. Applied in place of methyl bromide, Myrothecium eliminated the weeds in several field tests. After 14 days, no weeds were found and the tomatoes prospered. This research was part of an agency fast-track study to look for alternatives to methyl bromide-a widely used fumigant and ozone depletor. Methyl bromide is scheduled to be banned in the United States in 2005 and worldwide by 2015. Worldwide, 72,000 tons of methyl bromide are used in preplant and postplant applications and fumigations. The researchers are also examining several other possible, natural alternatives to methyl bromide for controlling weeds, including Fusarium solani and Colletotrichum truncatum.

Southern Weed Science Research Unit, Stoneville, MS
C. Douglas Boyette, (662) 686-5222, dboyette@ag.gov
Hamed K. Abbas, (662) 686-5222, habbas@ag.gov

ARS scientists have applied for a patent on a new insect diet that enables researchers to propagate destructive plant bugs that become lab food for beneficial insects. Scientists can raise pests such as the western tarnished plant bug, Lygus hesperus. This insect pest alone accounted for about $71 million dollars worth of cotton crop losses in 1998. Scientists want to mass-rear L. hesperus to serve as hosts for the production of parasitoids that could then be released to help reduce insect pest numbers in the wild. The key to mass-rearing these ravenous insects in sufficient numbers is developing a replacement for the plants they feed on. Without these special diets, rearing the insects is too costly. The new diet-fed insects are also used for research on sterile-release programs that had never before included Lygus bugs because they couldn't be reared in sufficient numbers. Sterilized plant bugs reared on the diet may mate and produce infertile eggs in the wild. This technology enhances the agricultural community's ability to mass-produce natural enemies of crop pests and decreases grower dependence on chemicals.

Biological Control and Mass Rearing Research Unit, Mississippi State, MS
Allen C. Cohen, (662) 320-7380, acohen@bcmrru.msstate.edu

Beneficial strains of Fusarium are being used to control Fusarium strains that cause wilt. The research is part of ongoing ARS research to use "good guy" biocontrol organisms against pathogens such as the wilt-causing Fusarium oxysporum. The successful tests are good news for tomato growers who need an alternative to the chemical fumigant methyl bromide now used to control wilt. Fusarium attacks many vegetables, melons, and other crops, such as basil, causing severe losses. Now, there is a new Fusarium strain that attacks tomatoes. The scientists tested several beneficial strains of F. oxysporum against the wilt-causing strain. They found one strain, CS-20, that reduced wilt by 49.6 percent. They also mixed beneficial strains of a fungus (Trichoderma virens strain G1-3) and a bacterium (Burkholderia vietnamiensis strain Bc-F). The fungus-bacterium treatment reduced wilt incidence by 41.6 percent. And CS-20 and the fungus-bacteria combination treatment significantly increased both the weight and number of tomatoes on the plant.

Biocontrol of Plant Diseases Laboratory, Beltsville, MD
Deborah Fravel, (301) 504-5080, fraveld@ba.ars.usda.gov