Beat the Heat: Corn and High Temps
Corn originated in the higher altitudes of central Mexico (7400 feet above sea level) so as you might assume, heat is not an ally. The question then is what happens when we have several days in a row at this growth stage that are excessively hot?
First, let’s look at how a corn plant responds to temperature. Corn development is based on a base 50 GDD calculation. That means anything below 50 or above 86 is not conducive to crop growth. For example, yesterday the high was 101 and the low was 72. Our GDD calculation would look like this: ((101+72)/2)-50 = 36.5 GDD’s. Except anything over 86 degrees isn’t counted (they actually are considered negative because of the stress) so we really have a formula that works out like this, (86+72)/2)-50= 29 degree days. You can see that we don’t accelerate growth by just having high daytime temps. However, anything above 50 is counted on the low side so temps above that at night do speed up development. Although low temps at or above 70 degrees (check your probe data to see how many nights you’ve had near 70 degrees) also allow respiration to continue at a high rate and some of the sugars made during the day are broken down at night.
Because corn is a C4 plant, it is very efficient in converting sunlight to sugar. But because of its high efficiency it is also adversely affected by high day time temperatures. High temps cause the plant to shut down early during the day and allow it continue to burn sugars during the night, a double “whammy” if you will.
Another thing to consider is our stage of growth. Much of our crop is now pollinating and heat can have some very detrimental effects here too. Today’s corn hybrids are bred with a longer ASI (anthesis-silk interval…time between mid-pollination and mid-silk) which means there are less problems today with “hitting the nick” or matching pollination with silking than there was, but it can still happen.
Stress, especially heat and drought stress together, slows down silking which if severe enough can cause the silks to not be fertilized. Temps over 95 degrees also slow down pollen-shed since there is less sugar being produced and stored by the stressed plant. You can sometimes see that in parts of the field that were sandier or compacted and have had artificial drought brought on. So certainly we want to make sure we are not stressing the crop for water. But, even when we have enough water, the heat alone can affect pollination. Under high temps the silks can desiccate and become unreceptive to pollen. Normally you see this more with low humidity not high humidity like we’ve been having. However, pollen shed is triggered by a drop in humidity. If we have continued high humidity and high temperatures, you may have little if any pollen shed as the anthers may just fall to the ground without ever opening and allowing the pollen to shed.
Unfortunately, the effects are also cumulative. With sufficient moisture, one day of temps above 95-98 degrees will probably have very little effect on yield. In fact, we can even handle a short string of days with very high temps. But for every day we have temps higher than 95 degrees we lose about 1% of our yield per day. And if we get past 6 days it could even double that.
This is why it’s so important to understand the stage of development of the crop and how much water is stored in the soil profile. Once we know that we can establish a safe zone for irrigation during pollination and prevent additional stress from too much or too little water. But, without those two pieces of information you are just guessing and you will either over or under water and either mistake could cost thousands of bushels.