The straighthead dates on the DD50 printout are not necessarily drain dates. It means that sometime during the timeframe listed the field should be in a drought stressed condition. As soon as this occurs, the field can be reflooded. Be sure and reflood by half-inch internode because any drought stress after this point can be very damaging. With the dry conditions over most of the county, corn irrigation is in full swing.
Irrigation is most critical when the water needs of the corn plant are greatest.
This period is from tasseling through ear filling when the water needs can be as much as 0.3 inches per day. Moisture stress anytime after planting can reduce yield. However, the amount of yield loss is dependent on the growth stage that the corn is in when moisture stress occurs. Research has shown the following relationships between yield reduction due to moisture stress and growth stage. Moisture stress that occurs prior to the tasseling stage can cause a yield reduction of 10 to 20 percent.