On August 1, Gary Guge, extension education director; Jeff Bradshaw, graduate student in entomology; and I visited a soybean field north of Little Sioux in Harrison County to view soybean leafminer injury. I must admit that I was skeptical of the amount and magnitude of injury that both Gary and the farmer had described to me over the telephone. When we entered the more than 60-acre field the plants were uniformly small (18-24 inches), mostly from a lack of sufficient moisture, and the entire field had an off-color, light green cast to it from the leaf injury caused by adult soybean leafminers.

Beetles seemed to be everywhere and the density ranged from 0 to 37 beetles per plant and averaged 5.4 per plant. Ten rows from the field edge, 10 sweeps with a net were taken down the row and produced six bean leaf beetles and 288 adult soybean leafminers. There was a small amount of bean leaf beetle injury (small round holes) in the leaves but a significant amount of injury was caused by soybean leafminers. The adult beetles scrape the leaf surface, causing the leaves to turn light green or white.

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Leafminer injury consists of scraping the leaves.

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Leaf injury from adult soybean leafminers (scraping) and bean leaf beetles (holes).

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A cluster of 37 soybean leafminers in the terminal of a soybean plant.

I would not expect this problem to be widespread; this is the first time that I have heard or seen significant soybean leafminer injury to soybean. Typically, some injury can be expected from the larvae during June and July, but adult injury across a field is very rare. Plants that are experiencing drought stress may have a greater probability for yield loss from this insect. Strong consideration should be given to the yield potential before a soybean field is sprayed for leafminers.