Keep fields relatively free of weeds. Weeds can make silage dangerous even though there is no nitrate in the corn itself. After a drought, plants rapidly take up nitrate following rain. So, harvest the crop before fall rains, or wait at least five days after a rain. Plants damaged by hail or frost should be harvested immediately before they take up nitrates.
Most nitrates are in the lower stalk.
However, take care to avoid possible exposure for 10 days after filling the silo, and when opening the silo for feeding. Small amounts of the gas may not be visible or easily detected by smell, but are still dangerous. Stay out of and away from the silo right after filling and during the following 10 days. If you must enter the silo. Never enter the silo alone during the danger period.