What to Do with Droughty Corn Fields?

It doesn't take a long drive around the state for one to encounter some "pineapple" corn fields. The U.S. Drought Monitor map shows that, in the last 30 days, some regions in the state have received only 25% of the amount of rain they normally get (Figure 1). Many fields have just passed the silking stage, which is when the crop is most susceptible to drought stress.

Figure 1: Precipitation received in the 30-day period between July 10 and August 9 as a percent of normal precipitation. Source: USDM, accessed on August 15, 2022. Photo Credit: U.S. Drought Monitor (droughtmonitor.unl.edu/About.aspx)

Dealing with the drought

We have published a few articles on how to deal with prolonged drought at this time of the year (see links at the end of this article). Here is a summary of the steps one can take to decide on what to do with drought stressed corn fields.

1) Assess grain yield potential

Scout the fields to estimate the impact of drought on yield. While estimating yield before the milk stage is not easy, it is possible to check for signs of a severely stressed crop. When the top leaves are rolled for many consecutive days (and do not unroll during the night) and show discolorations (grey, brown), yield will likely be very low and grain harvest may be off the equation. If conditions are not so bad, one can do the ear-shake test, as explained in this video by Dr. Bob Nielsen from Purdue University. This test can be done a few days after silking to estimate the percentage of the ear that was pollinated. It is important to consider that even if pollination was successful, fertilized ovules can be aborted in the few weeks after fertilization (blister and milk stages) due to continued drought.

2) Harvest for silage (or green chop)

If your estimated grain yield potential is not promising, an option for those droughty fields is to harvest them for silage. Drought stressed corn is often higher in crude protein and the net energy content is usually 85-100 percent of normal. Drought-stunted corn silage often contains high fiber digestibility, so when it is supplemented with additional grain, it can be an excellent forage. One concern is that nitrate concentration may be high in drought stressed corn, especially in fields that received high levels of nitrogen fertilizer or manure. Nitrate levels can increase further after a drought ending rain, which can trigger nitrogen uptake from the soil. In these situations, it is a good practice to obtain a forage nitrate level test and avoid ensiling following the rain. All of these considerations are also valid for green chopping the corn and feeding it directly to animals, with the additional note to check pesticide restrictions when direct feeding.

3) Plant a fall forage crop

The prospect of obtaining additional forage after an earlier-than-expected corn harvest depends on many factors, such as: soil moisture after corn harvest, expected maturity time in relation to fall frost date, end use goal, herbicide carryover from the corn crop and other rotation considerations. Check herbicide labels for plant-back intervals and keep in mind that dry conditions delay the breakdown of atrazine in the soil and increases the potential for crop injury. Below are some popular options for a late summer planting after corn silage harvest:

• Forage Brassicas (e.g., rape or turnip): these are a good option for grazing systems. They are fast growing and typically are ready for grazing 6-8 weeks after planting. They also have good cold tolerance which provides extended grazing time thru the late fall.
• Sorghum-sundangrass: this is a good option for ensiling and has good drought tolerance and low risk of atrazine injury. However, planting this crop in August may not be an option in colder counties as it will likely not be ready for ensiling before the fall frost.
• Spring oats: this is also a good option for ensiling and may be ready for harvest before sorghum-sudangrass. However, this may not be an option if atrazine was applied just before corn planting. Check herbicide labels for rotation restrictions.

Links to other Penn State articles on drought stressed corn and replanting options:

Managing Crops in a Severe Drought

Salvaging Drought Stressed Corn for Silage

Fall Forage Options Due to Droughty Conditions