Scrutiny of root-nibbling pathogens, plucked from strawberry roots in one of the nation's leading strawberry-producing regions, will provide new clues about how to foil these destructive crop pests. Scientists are determining the abundance and virulence of soil-dwelling pathogens Pythium and Rhizoctonia. This should help them develop new tactics for killing these and other microbes. New weapons are urgently needed because strawberry growers' most effective tool—methyl bromide fumigant—is being phased out. The researchers are sampling microbes from commercial strawberry fields along the central coast of California—the nation's No. 1 producer of strawberries. Pythium and Rhizoctonia microbes that scientists are examining cause a strawberry disease known as black root rot and can also infect lettuce, tomatoes, cauliflower and many other plants. Severity of strawberry plant symptoms varied greatly when researchers used field samples of the microbes to infect greenhouse strawberry plants. Pythium ultimum—the most prevalent Pythium at field sites—and P. irregulare were among the Pythiums causing the most damage to greenhouse plants. But several other Pythium species that were brought in from the strawberry fields caused few if any symptoms. In contrast, nearly every Rhizoctonia form recovered from the field significantly reduced growth of the greenhouse-grown strawberry plants.

Crop Improvement and Protection Research Unit, Salinas, CA
Frank N. Martin, (831) 755-2873, fmartin@asrr.arsusda.gov

Genetically engineered peanuts may offer a new defense against one of the legume crop's most costly foes: the larvae of lesser cornstalk borers. Unchecked by soil insecticides, the pests eat pods that house the peanut plant's seeds, rendering them inedible. To deter such attacks, ARS and university researchers genetically engineered peanut plants to make a protein from Bacillus thuringiensis (Bt) bacteria. Borers that ingest the plants' Bt proteins generally stop attacking or starve. In 1998 field tests, 90 percent of the Bt peanuts escaped serious pod damage from borer attack compared to an unaltered control group. Scientists are now analyzing data from a second round of tests from last summer. Commercial peanuts bred from such plants could help cut insecticide use, prevent aflatoxin contamination by Aspergillus fungi, and slow the cornstalk borer's ability to overcome resistant cultivars that are now available.

Insect Biology and Population Management Research Laboratory, Tifton, GA
Robert Lynch, (912) 387-2375, rlynch@tifton.cpes.peachnet.edu

Sugarbeet growers may soon get a new tool for identifying six major types of fungi that can seriously damage their crop. Using polymerase chain reaction (PCR) technology, ARS scientists have developed a way to quickly identify six kinds of fungi that can cause multimillion-dollar losses in U.S. sugarbeets. The whole diagnostic process can be completed within 8 hours. PCR reproduces millions of copies of the unique segments of fungal DNA that occur in a plant tissue sample. With this amplified DNA, the researchers can quickly distinguish the pathogens according to their DNA "fingerprints," generated when the DNA is cut into pieces with an enzyme. By using PCR, scientists don't have to isolate fungi from diseased roots or leaves and spend days culturing them before they're identified. Rapid DNA identification of offending microbes would tip growers off to the need for control measures before fungal diseases seriously curtail yields. Now, ARS scientists are narrowing down DNA identification even further, to identify species as well as genera. Already the scientists can distinguish Aphanomyces cochlioides, which causes black root disease of sugarbeet from A. euteiches, which causes root rot in peas and other legumes. Other fungi that attack sugarbeets include Pythium ultimum, Cercospora beticola, Phoma betae, Fusarium oxysporum and Rhizoctonia solani.

Sugarbeet and Potato Research, Fargo, ND
John J. Weiland, (701) 239-1373, weilandj@fargo.ars.usda.gov

ARS scientists have begun a 3- to 4-year project to find ways to combat the tarnished plant bug, Lygus lineolaris, a major cotton pest that cost growers $75 million last year. The study covers a 36-square-mile area in the Mississippi Delta region, consisting of four 9-square-mile areas, with a possibility of future expansion. In 1993, an ARS researcher discovered tarnished plant bugs had become resistant to pyrethroids, a class of insecticides commonly used to control them. There are more than 100 different weed species on which tarnished plant bugs can feed and reproduce. In the winter, they lie dormant in weeds surrounding cotton fields and emerge from February or mid- to late March and begin laying eggs in the weeds. In late spring, they move into cotton crops when the weeds mature. ARS scientist are investigating several different approaches to controlling plant bug populations, including controlling weeds, using biological controls, and developing a chemical lure called a pheromone. It has been know for several years that the female produces a pheromone that attracts mostly males. However, in field tests last summer, ARS scientists discovered that the males may produce a pheromone that attracts both sexes—probably to signal food sources—but they are repeating the test this summer to make sure. Tarnished plant bugs are the only major pest in cotton for which scientists don't have a sex pheromone. Once they develop one, they'll be much closer to banishing the pest from cotton fields.

Southern Insect Management Research Unit, Stoneville, MS
Gordon L. Snodgrass, (601) 686-5231, gsnodgra@ag.gov