Triangle pest control7/20/2023 ![]() ![]() Drought stress, along with heat, led to problems with spider mites, which love hot, dry weather. ![]() In some fields, cooler temperatures in August helped aphids build beyond economic thresholds and required treatment, Hodgson adds. Insecticide seed treatments and host-plant resistance also helped slow aphid development and spread during the spring and early summer." In 2011, temperatures above 90☏ in July kept populations from building up. "But population growth during the summer is determined by temperature. "Being cold-hardy, soybean aphids can overwinter almost anywhere," Hodgson explains. But whether the other insects reach problem levels depends on local weather conditions-the third link in the pest triangle. The presence of black cutworms in any field is governed by weather patterns as the moths migrate northward (along with weedy habitat in those fields). A few Iowa growers had to make late-season applications to control bean leaf beetles attacking soybean pods. Some Iowa growers had to replant fields because black cutworms reduced their soybean stands, Hodgson con-tinues, and some growers had to spray for spider mites. But not every field needed to be treated-although I hope every field was scouted." "They showed up first in Minnesota, and then were found in most north-central states. "In Iowa, soybean aphids were the most prominent soybean insect in 2011," explains Iowa State University Extension entomologist Erin Hodgson. In the Midwest, most soybean insect and disease problems in 2011 were found to be localized. But they are not considering the potential negative long-term consequences of unneeded pesticide applications: the reduction of natural predators and the development of resistance by the pests." "Many believe just a few more bushels per acre will at least cover the cost of the treatment. ![]() "Farmers have more acres to take care of and they are looking at high commodity prices," Gray says. "But we feel there should be a demonstrated need, based on threshold levels of a pest." "At current crop price levels, you can understand farmers’ thinking," Baer says. Prevention without evidence of a threat is not a sound basis for treating, agree Baer and Gray. "With current soybean prices, some growers are inclined to spray preventively, rather than basing their decision on scouting and economic return," says Mark Baer of Sun Ag Supply in Tremont, Ill.īasis for treatment. "Conversations with my colleagues, and the number of aerial applicators I see spraying fields, convince me the frequency of fungicide applications is increasing," says University of Illinois Extension entomologist Mike Gray. The pest must be present and the environment must allow it to reach a damaging level before treatment is justified.Īnecdotal evidence suggests that a lot of farmers could have saved a lot of money if they had considered the triangle in 2011. The answer, of course, is (c), and the triangle consists of the host, the pest and the environment. Quick quiz: The pest triangle is (a) an alarm you ring when you spot bugs in your soybeans (b) a romantic conflict involving three Japanese beetles or (c) a set of factors that helps farmers determine whether an insect or disease is reaching problem levels. Spray only the fields where diseases, insects are present
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