Duane Dailey Senior Writer 573-882-9181 DaileyD@missouri.edu July 19, 2005 Colony of soybean aphids provide new teaching aid at MU Pest Day; no Asian soybean rust for viewing COLUMBIA, Mo. - Soybean aphids: yes. Asian soybean rust: no, not yet. Farmers heard crop pest updates during field day tours at the University of Missouri Bradford Research and Extension Center, July 14. Tom Clark, MU entomologist, showed visitors a soybean plot infested with an estimated 6,000 aphids per plant, far above the economic threshold for spraying an insecticide for control. At the next tour stop—on Asian soybean rust—Laura Sweets, MU Extension plant pathologist, said, "No news is good news." However, she said the passage of the remnants of Hurricane Dennis has lead a network of MU Extension agronomists across the state to increase the frequency of monitoring soybean fields for signs of the fungus, spread by windblown spores. Sweets showed a map of counties where soybean rust has been confirmed in the southeastern United States. All are in Florida, Georgia, and Alabama. Next, she showed a map with the track of Hurricane Dennis. The storm's path took in those southeastern states, and ended in southeast Missouri. While the potential is high that rust spores were moved by hurricane winds, known infestations have not been prolific spore producers. "The surprise has been how slowly rust has spread," Sweets said. Infestations in Florida, which were detected early in the year, have been mainly on kudzu and spread to only one soybean field in that state. Of more immediate concern are soybean aphids, Clark said. The pests, accidentally imported from Asia into the northern United States several years ago, are being found in Missouri fields, and had heavily infested a small area of plants in a soybean plot behind Clark's tour stop. The aphids appeared since the field was inspected a week earlier. Aphid counts on the plot at the MU farm east of Columbia were far above the threshold of 250 aphids per plant recommended for applications of controls. Several insecticides are approved to control soybean aphids. Northern winds carry aphids, small light-green to almost colorless insects, from Iowa, Minnesota and Canada. There, overwintering populations were higher than normal this year. Wayne Bailey, MU Extension entomologist, said, "It is highly likely that we will have large infestations of aphids this year." Aphids give birth to live young, instead of laying eggs, and can start reproducing within a day of birth. As it happened, the aphids landed on Bradford plots to be monitored to study the economic threshold under Missouri conditions. "We've adapted the thresholds from research in northern states and Canada," Bailey said. "Since we haven't had widespread populations of aphids, we've not had research on the threshold in Missouri." Aphid infestations requiring treatment have occurred only twice in Missouri. "We expect the problem to be more widespread this year, maybe statewide," Bailey said. At the tour, Clark said, "Anyone who has not seen soybean aphids can come look." Everyone piled off the tour wagon. While the aphids are difficult to see, Clark advised visitors to look for ants and ladybugs first. "They are easier to see. The ants eat the honeydew produced by the aphids. Ladybugs eat the aphids." Clark then turned over soybean leaves to reveal thick colonies of aphids. The insects live on the underside of the leaves. Natural predators keep most Missouri aphid infestations in check. "The ladybugs probably can't keep up with an infestation this big," Clark said. MU researchers plan to start spraying the infested plot. In the past, the annual Bradford field day concentrated on weed research, said Kevin Bradley, MU Extension weed specialist. However, the event now covers all crop pests, including diseases and insects. The Bradford farm is part of the MU Agricultural Experiment Station network of research centers located across the state. Source: Tom Clark (573) 884-5125; Laura Sweets (573) 884-7307; Wayne Bailey, (573) 882-2838 Return to Current News Releases College of Agriculture Food and Natural Resources AgEBB