The droughty summer weather might make cornfields look dry enough to harvest for silage, but looks can be deceiving. Farmers should take time to test for whole-plant moisture levels before they begin chopping.

"The question comes up of when to harvest for silage corn that has gone through drought stress," says Herb Bucholtz, Michigan State University professor of dairy nutrition and animal science. "The answer is no different than when trying to harvest normal corn for silage."

Corn silage should be harvested when the whole-plant dry matter is between 30 and 35%. Dry matter content is important for the bacterial fermentation that takes place in the silage process.

"If it's drier than that, you will not get as good fermentation, material will not store as well and may spoil, and you may get a decrease in the digestibility," Bucholtz says.

Though a field full of curled-leaved stalks might look dry enough, the plants themselves might still harbor too much moisture, and an accurate test is needed. To test corn moisture levels, producers should select and chop 15 to 20 plants from various parts of the field. They should test those plants using either a Koster moisture tester or a scale and a microwave oven. Directions for testing are

Once the moisture content begins decreasing, farmers should monitor the fields every few days to gauge the drying rate and begin to predict when to harvest.

"That rate of drydown on corn plants will differ from field to field, farm to farm and variety to variety," Bucholtz points out. "Producers have to monitor conditions for their individual farms -- they can't even count on doing what their neighbors are doing."

High plant nitrate levels are a concern with drought-stressed corn. Normally, corn plants process nitrates into harmless proteins, but drought-stressed plants don't have enough moisture to carry out the conversion. Experts recommend waiting two weeks after rainfall before harvesting drought-stressed corn or forage crops to allow time for the recovering crops to convert the nitrates into usable proteins.

"Timing is everything," says Ken Rauscher, director of the Michigan Department of Agriculture Pesticide and Plant Pest Management Division. "Delaying the harvest of drought- stressed corn, especially if the crop has been rained on, reduces the risk of nitrate toxicity to animals."

And though farmers might be tempted to harvest corn higher off the ground than normal to lower nitrate levels, the normal 4- to 6-inch level should be maintained to avoid unnecessarily losing yield.

Nitrates are potentially toxic to cattle. Feeding green chopped corn plants, grazing them or feeding unfermented corn silage or sorghum sudan is not recommended. After the ensiled material has undergone three to four weeks fermentation, the nitrate levels will be reduced. If producers are concerned about nitrate levels in their silage, they may submit samples for testing at the MSU Plant Diagnostic Laboratory.

Producers who are concerned about nitrate levels in their silage may submit samples for testing at the MSU Plant Diagnostic Laboratory.

After the silage sits in storage following fermentation, it needs to age. Bucholtz recommends letting it sit for three to four months, if possible, to enhance

For more information about preharvest corn testing, contact your county MSU Extension office or the MSU Plant Diagnostic Laboratory Web site at www.css.msu.edu/SoilTesting.cfm.  

MSU offers a number of resources for farmers dealing with drought issues. Fact sheets related to drought and forage crops can be found on the MSU Beef Team Web page at beef.ans.msu.edu/Drought/drought.htm. Resources on corn and other crops can be found on the Crop Advisory Team Alert site at www.ipm.msu.edu/drought2007.htm.