Submitted by Wayne Flanary
This year, I have been scouting area corn and soybean fields for the University of Missouri weekly and providing reports of what I find. The sites are in Andrew, Buchanan, Holt, and Atchison Counties. The Holt County site also has an irrigated site.
Area corn crops are proceeding with corn in various stages of ear development. It is obvious when looking at corn fields that some producers are using resistant hybrids to manage gray leaf spot. For example, in one field where corn is continuous, little to no gray leaf spot and another hybrid in no-till corn and soybean rotation has lower leaves infected.
Gray leaf spot is only on lower leaves three of scouted corn fields and on only one field with less than one percent infection on third leaf below ear leaf. Disease progress is slow. All other fields have no infection as of July 22.
Japanese beetle is not at economic threshold and corn is pollinated in fields that have been scouted. One field had severe silk clipping, but this was after pollination. Unfertilized silks will remain attached to the embryos and test pollination by dangling the ear from the butt and determine which silks remain and those which fall off.
When scouting for corn diseases, look at the ear leaf for disease and the three leaves above and three leaves below the ear leaf for disease. Watch if any disease is progressing. Gray leaf spot moves upward on corn and common rust will be on upper leaves.
As far as soybeans, soybeans are progressing rapidly, and most fields are in reproductive stage. In the fields scouted, one can confuse herbicide injury to leaves to lower leaves so examine plants carefully. Septoria leaf blight has been found on two fields, but this was on lower leaves which senesce as plants grow so no impact on yield.
Fields scouted so far do not have any foliar disease present. Hot temperatures are not conducive to disease development.
Japanese beetle populations have peaked and will start declining. Defoliation by this pest will leave leaf veins and consume area between the veins. Economic threshold is 20% defoliation for soybeans in the reproductive stage. When considering defoliation, examine all leaves of the plant, not just the top.
For more information, contact Wayne Flanary, Field Specialist in Agronomy, University of Missouri Extension, cell phone 913-220-2670 or Buchanan County Extension at 816-279-1691.
