Agronomists and producers should be aware that on June 1st, Dr. Eileen Cullen discussed with University of Wisconsin Extension Agents that both soybean aphids and potato leafhoppers have been found on West Madison UW Research Farm.
Soybean growers and alfalfa growers should not be alarmed, but they should work with their agronomist to plan monitoring these pests this season. The aphid numbers reported are in the one to 13 aphids per plant range. Producers are reminded that the threshold for soybean aphids is 250 per plant and increasing. Even though this year, 2007 is an odd numbered year, there are some folks who hold the thought that aphids are at higher populations every other year. In 2005, there was significantly more aphid spraying than there was in 2006. The only way to really know if your soybeans need aphid control is to scout. The other interesting difference this season is the dramatically reduced acreage of soybeans available since growers are producing more corn this season. Does this mean that fewer acres of soybeans will have more aphid pressure? Nobody knows, so you should make arrangements for scouting.
Since potato leafhoppers have arrived it is important for alfalfa producers to realize that yield and quality losses occur from this pest prior to the visible sign of yellowing leaves and stunted plants. The only way to know if leafhoppers are at economic treatment levels is to scout using a sweep net. Growers should spray insecticide if there is one potato leafhopper in 10 sweeps per inch of alfalfa height in susceptible alfalfa varieties. Research has shown that leafhopper resistant varieties can tolerate generally three times as many potato leafhoppers. Keep in mind that new alfalfa seedlings are most susceptible to leafhopper damage.
If you have further questions about these pests, contact your local UW-Extension Agent.