David Owens, Extension Entomologist, owensd@udel.edu
Alfalfa
Potato leafhopper counts from this week were a good bit higher than two weeks ago. Scout short alfalfa now for leafhopper. In our management guide, there is a threshold table relating leafhopper count, size of alfalfa, and control cost with the justification for a treatment. Please note that if alfalfa was harvested early for its first cut, it should not be cut early again. Please also note that the table may not accurately reflect current prices received for alfalfa hay, it needs to be updated, but you can use it to get an idea of what a more applicable threshold should be. Insect_Control_in_Alfalfa_-2023.pdf
Soybean
Continue scouting for general defoliation, but remember, defoliation thresholds are very high in full season soybean. The earliest planted full season beans are flowering, thresholds on reproductive stage soybean decrease to 10% (this is still very conservative). Mites may be a concern, especially around field edges with hot, dry weather setting in. Beans that are flowering should also be scouted for stink bug, especially in the east Laurel/Gumboro/Delmar triangle area and the western Greenwood area. I’ve mentioned studying prophylactic soybean sprays before. In one field site, there was a small reduction in stink bug numbers in areas that were treated earlier with a pyrethroid, but those strips and the rest of the field still went over the traditional 5 stink bug per 15 sweep threshold. As a general rule, I do not recommend tank mixing a pyrethroid with a herbicide or fungicide unless the population of stink bugs is greater than 2 per 15 sweeps. There is also a risk to damaging pollinator activity in flowering soybean with such a tank mix. There are some studies that suggest that pollinators are responsible for a fairly sizeable portion of soybean yield.