Getting an Early Jump on the Soybean Aphid

WOOSTER, Ohio — Crop growers may still be waiting for their fields to thaw, but Ohio State University research entomologists are already putting the bug in their ear regarding the soybean aphid — the soybean plant’s new and most mysterious pest. Ron Hammond, an Ohio State research entomologist with the Ohio Agricultural Research and Development Center, is hoping that early reminders will get growers thinking ahead to scouting and managing for the pest, which took upwards of 15 bushels of soybeans per acre away from growers in some fields last year. “This insect has been around in Ohio for four years now and there are still many things about it we don’t know,” said Hammond. “We are still learning and will be learning more about the insect in the years ahead.” The soybean aphid is a sapsucker, feeding on the soybean plant and causing stunting, yellowing of the plant and leaf distortion. If enough aphids attack a plant, they reduce the vigor of the plant, eventually leading to yield losses. Since the aphid was discovered in the United States in 2000, it has been found as far north as Canada and as far west as Nebraska and the Dakotas. Hammond said that he and colleagues from other soybean aphid-infested states meet regularly to compare research findings, management techniques and the differences in crop performance, all with the intention of laying a control groundwork for producers. One aspect that researchers have come to a consensus on that could aid soybean growers in effectively managing the soybean aphid is the establishment of insect population thresholds. “We believe that the threshold is 250 to 300 aphids per plant before there is an impact on the plant,” said Hammond. “It’s the threshold we used last year and we are going to stick with that this year.” Hammond encourages growers to keep this threshold in mind when they begin scouting their fields in early July during the soybean plant’s flowering stage through the pod development stage. “We want growers to be scouting on a regular basis so if and when aphids reach that threshold, growers will be able to determine if populations continue to rise throughout the season, and what action they need to take to control the insect,” said Hammond. One thing researchers have discovered is that the insect behaves differently in different states. That is, populations may be waning in August in Minnesota or Wisconsin when things are just starting to get active during that time in Ohio. “When it comes to recommendations, we have to make sure that we what we say holds true for Ohio and other eastern Corn Belt states. Management practices in western Corn Belt states may not be suitable for Ohio,” said Hammond. Researchers are curious to see what 2004 will bring in terms of soybean aphid populations to determine whether current theories about the insect will be upheld. “In 2001 we had high populations, 2002, low populations, 2003, high populations — what’s going to happen in 2004? Current thinking is that we may not have a problem this year with the soybean aphid,” said Hammond. One speculation is that soybean aphid populations are tied to the multicolored Asian lady beetle, a predator that feeds on the aphid. Observations from other states suggest that the Asian ladybeetle may be feeding on overwintering soybean aphids, thus reducing their populations when the next growing season approaches. “Whatever this new season has in store for us, growers should not shirk scouting their fields,” he said. Hammond said that there is also some speculation that most of Ohio’s soybean aphid populations don’t overwinter in the state, but are carried south on wind currents. “If we can establish this hypothesis, and if reports from more northern areas indicates soybean aphid populations are high, then we have a bit of warning and can prepare in advance for potentially high populations in Ohio,” said Hammond. “Aphid populations from northern states seem to build up quicker and show up earlier in the season than populations do here.” For more information on the soybean aphid, log on to Ohio State Extension’s Integrated Pest Management Web site at http://www.ag.ohio-state.edu/~ipm/.