Case Details
Soybean Problem(s)
Submitted by Jerome R. Clark on 9/11/2009
Conventional soybean planted into corn about mid-May. Outlook and First Rate applied pre-emergence. Many lambsquarters escaped control. About 1/4 of field looks like these samples. Many aphid skins. No visible sign of BSR. Japanese beetle feeding on some leaves.
Problem a result of combination of poor weed control, dry weather, and an aphid outbreak?
Reply by Chris M. Boerboom on 9/13/2009
Jerry, without seeing a photo of the weeds in the field, it is hard to say how much of the poor growth is due to weed competition. It appears that there are at least three main stresses on the soybeans - weeds, drought, and aphids. Lambsquarters and drought can cause a lot of damage, especially on lighter soil. One question to help sort out the situation is if the soybeans with heavy damage (i.e. these 1/4 of the plants) have as many escaping lambsquarters as the remaining 3/4 of the field. I would also double check on fertility.
Chris
Reply by Eileen M. Cullen on 9/14/2009
Hello, Jerry. Soybean aphid is a contributing factor. Two of your photos show sooty mold growth on the leaves. Drought, and potentially fertility, (+Chris' comments on weeds) are combined stress factors. Good idea to double check fertility as low K can lead to increased aphid. Was this field treated for aphid earlier? In the 3/4 of this field not affected by the pictured symptoms, do you have some evidence of aphid as well? (soybean aphid does not cause leaf necrosis). If you have aphid cast skins and/or sooty mold in the other 3/4 of the field, but plants are otherwise "non-stressed", - that could help further separate main stress factors in affected 1/4 area. - Eileen
