By Liz Stahl and Anthony Hanson et.al
Soybean aphids, unconventional treatments, and crop diseases were the topic of conversation on the August 12th Strategic Farming: Field Notes program. Drs. Anthony Hanson, Extension Educator – Integrated Pest Management, and Dean Malvick , Extension Plant Pathologist, joined Ryan Miller, Extension Educator-Crops to discuss these issues and more.
Soybean aphid populations have been low
Hanson reported that although soybean aphid populations have generally been low to date, he has seen numbers increase in some fields. Aphid reproduction is slow when temperatures are in the 90s and nights are warm. Although recent cooler temperatures increase the potential for populations to increase quickly, we are getting near the end of August, so aphids should be moving to buckthorn soon. As the season continues to progress and soybeans reach the R6 stage (full seed), the economic threshold bumps up beyond 250, and insecticide applications are often not needed at this time as aphids also start to migrate back to buckthorn around late-August.
Although the decision of whether or not to treat can get tougher as soybeans mature, if the economic threshold is reached just before R6 stage, one can treat for soybean aphid if populations reach threshold. The economic threshold (average of 250 aphids per plant, with 80% of the plants having aphids, and the population is increasing) is there to help protect yield and give enough time (5-7 days) to arrange an insecticide application before populations reach economically damaging levels around 670 aphids per plant. See Late-season soybean aphid scouting and management for a more detailed discussion that includes information on product selection. Pre-harvest intervals need to be taken into account as well as we get closer to the end of the growing season.
Source : umn.edu