By Lori EhdeThe Minnesota Department of Agriculture is warning soybean growers to scout their fields and be prepared to take action to control soybean aphids, which are reaching near-record levels in local fields.Wednesday night last week, Bruce Potter of the University of Minnesota, spoke to Rock County soybean producers on the Jeff Thorson farm about the aphid threat.Some local fields have seen infestations of more than 1,000 per plant, while others are at a less-threatening 200 to 300 per plant.In most cases, however, producers are opting to spray their fields, because infestations can multiply rapidly. One Rock County producer reportedly noted 50 aphids per plant on Aug. 8, and four days later, there were 250 per plant.Rock County soybean producer Steve Tofteland attended Wednesday’s meeting on the Thorson farm and said many farmers are opting to spray their fields."We’re seeing bean leaf beetles, too, so you can get them both if you spray," Tofteland said. "Plus, it’ll get the grasshoppers, too."Depending on the level of infestation, farmers can see five to eight bushels per acre yield loss if the soybean aphids are left untreated."Some have seen a 14-bushel loss, compared to treated plants in the same field," Tofteland said.That, he said, makes it worthwhile to consider the cost of chemical application. It costs roughly $9.50 to $13 per acre, respectively, for ground and air applications.By mid-week last week, many local ag chemical businesses were getting behind on ground applications, and local residents are noticing low-flying planes applying from the air.Harlan Solma, who applies chemicals for Farmers Union Co-op Oil customers, said he’s sprayed 20,000 acres in Rock County last week, he anticipated another 10,000 this week. He said there are roughly 90,000 acres of soybeans planted in Rock County this year.Over the last few weeks, MDA Plant Pest Survey staff reported dramatic increases in soybean aphid levels in southeast Minnesota.Recent data shows dramatic increases in soybean aphid levels in southeast Minnesota over the past few weeks, and they’re on the rise in western and northern Minnesota. In many areas, this year’s population levels now rival — and in some areas surpass — those of 2001, when the aphids caused considerable damage to crops.Most Minnesota soybean fields are now blooming and setting pods. At these stages of growth, it is critical to protect plants from heavy aphid pressure.Producers urged to monitor soybean plantsMDA Pest Survey Coordinator Mark Abrahamson recommends growers monitor and evaluate numbers of soybean aphids in their fields at least once a week in areas where aphids are not abundant.He suggests they monitor more frequently in areas with greater aphid numbers."One of the toughest parts of dealing with soybean aphids is that infestations can be unpredictable," Abrahamson said. "Regular monitoring is crucial because aphid levels can vary drastically from field to field. Last week we found two fields near East Grand Forks with thousands of aphids per plant while nearby fields were barely infested."Depending on weather and other factors, heavy aphid infestations can cause up to 20 percent yield loss. When populations rise above certain thresholds, it is considered economical to conduct treatments. The following thresholds are suggested by University of Wisconsin and the University of Illinois experts: 200 aphids per plant during bloom, 1,000 aphids per plant during early pod set, and 1,500 aphids per plant during late pod set.Abrahamson notes that before taking any action against a soybean aphid infestation, farmers should closely examine a number of aphids to determine if they are developing wings. Crowded conditions will cause aphids to begin having offspring that grow wings and disperse from the field. Treatments are generally not recommended if aphids are winged as they will likely be leaving the field soon anyway.Growers can find out more about soybean aphids and their management through the following Web site: www.soybeans.umn.edu. Weekly updates on major Minnesota crop pests are also available from the Minnesota Pest Report, a free weekly publication published by the MDA Plant Pest Survey Program that is available electronically or in hard copy.To subscribe, contact Mark Abrahamson at 651-296-6509 or via e-mail at mark.abrahamson@state.mn.us
