Hardly a crop season goes by without one pest or another, sometimes one not expected to be a problem, rearing its ugly head, just in time to reduce corn stands. This year's prime candidate, at least in parts of Indiana, may be white grub. While much of the damage is likely already done, it could explain thin stands if you discover them later while walking fields.
Jeff Phillips, Tippecanoe County Extension ag educator, and Charlie Padgett of Buck Creek Crop Production Services visited fields within the last 10 days that showed definite signs of grub damage. In fact, several of the stunted plants were cut at soil surface level or just below. Many times they would find a large white grub in the soil near the plant.
The condition was most extreme on sandy soils, and less visible on soils with more loam content. That matches reports form northern Indiana soil consultants, who contend that white grubs were a real problem on sandier soils in their area this year.
These grubs will later turn into Japanese beetles. Whether or not finding them now indicates high counts of Japanese beetles later is unclear. The main damage from Japanese beetles in corn occurs if they clip silks. Corn is not the preferred pest for Japanese beetles, but they will clip silks if they have nothing else to feed on. The best advice will be to monitor fields carefully at pollination time to make sure silk clipping is not occurring, or is at least not occurring at an economic level.
Grubs weren't the only problem Phillips and Padgett found in the field. They also discovered signs of fertilizer burn and wireworms, amongst other things. The farmer applied about 11 pounds of nitrogen per acre with a split-bander attached to seed firmers. The goal was to place it on either side of the seed.
The Purdue University Corn & Soybean Field Guide notes that in dry weather, the risk for salt injury is greater. It was very dry since planting. Plants that were putting out a root, not affected by grubs, were likely affected by salt injury, the pair concluded. They also surmised that if it rained, those with roots that were already establishing themselves should grow out of the problem.
Their advice was to leave the field. Overall stand count was over 20,000 plants per acre. Replanting at such a late date, say June 5, gives you a hard hit on yield potential for late planting, even if you get a perfect stand the second time. That might not happen.