Lodged Soybeans? Threecornered Alfalfa Hopper May Be the Culprit

Reports have been coming in across the Coastal Plains and Blacklands concerning lodged soybeans.  Most of these can be traced to threecornered alfalfa hopper injury that occurred in the weeks prior.  Threecornered alfalfa hopper injury is not often visible until later in the season, as plants get some size and people begin to notice some lodging.  With the strong summer windstorms, plants have been given a push and this lodging has been apparent earlier than usual.

Threecornered alfalfa hopper injury. Note the calloused tissue, a plant response to the piercing sucking feeding of this insect. Image from David Adams, University of Georgia, Bugwood.org.

Threecornered alfalfa hopper injury typically occurs as a girdle around the stem above the soil line.  This likely occurred when the plant was small (under 10 inches).  These insects will continue to feed as the plants grow, but will feed on and injure petioles on the main stem.  This can block the vascular tissue of the beans, causing indirect yield loss.  More often, loss is direct when plants lodge during harvest.  The breaking point from the lodge is often a distinct and clean break that occur at the feeding site (a few inches above the soil line).

Because the lodged plants we are seeing now resulted from earlier injury, scouting is really important.  If the plants are too big or the insects are no longer present, you’ll be wasting a revenge spray. Plant growth stage is also important since vegetative soybeans can compensate for injury.  For example, if 10% of the stand has lodged and the beans are early in the vegetative stages, it is likely that adjacent plants will compensate for yield.  To see if the insect is still present, use a sweep net and treat only if you find at least one threecornered alfalfa hopper per sweep (swoosh of the net).  Pyrethroids work well, with bifenthrin and pyrethroid/neonicotinoid mixes working a bit better.

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