AE-78 Sept. 1970
Bruce A. McKenzie and Clarence B. Richey Extension Agricultural Engineers, Purdue University
GENERAL SITUATION AND RECOMMENDATIONS
Stalk rot and cob rot in heavily blighted corn is generally severe, and the stalk and cob rot develop exceptionally fast. In addition,lodging is potentially very severe.
It seems likely that heavy foliage from rain or snow, accompanied by wind could lay some fields almost flat. Stalk rot appears so severe in some fields that it seems likely that many stalks may break off before or during harvesting, causing excessive loss and clogging.
The stalk and cob rots are also present in the ear shank, so ears in some fields will ^op readily before or during harvest. The cob rots also destroy the central core of the c°b. In advanced cases cobs are spongy or rubbery when twisted or flexed, and can be easily crushed by squeezing. The rotted cob simply has no crushing strength, and will not withstand the pressures necessary lor shelling. It will shatter and go through toe cylinder without complete shelling.
A number of secondary ear molds are Present on the corn kernels and exposed cob surfaces in the field in addition to the fungus
Helminthosporium maydis, that causes the original disease. These molds will tend to stabilize and stop growing when kernel moisture content reaches 25 percent to 21 percent in the field accompanied by lower fall temperatures. Bear in mind that cob moisture contents can still be higher when the kernels have dried to this level.
At regular intervals farmers should observe their fields closely to gain a good estimate of the rate of development of these factors. Observations should be made within the field away from the outside rows. Outside rows develop and dry differently because of their increased access to light and air. To gain an estimate of percent stalk rot present pinch stalks near the ground and up toward the ear for a distance down the row.
A hollow shell that collapses easily indicates advanced rot. Rill ears that are representative of the different field conditions and flex, twist, and break cobs to look for rot. Squeeze the ears to test crushing strength which will help indicate when to start the harvest to minimize losses. Note dropped ears and shake stalks to estimate shank rot/ear drop.
Cooperative Extension Service, PURDUE UNIVERSITY, Lafayette, Indiana