Global warming advocates aren’t saying much about the weather these days because cold weather has pushed well into spring. I heard someone on a morning show comment that “Punxsutawney Phil, aka The Groundhog had missed the target this year and might be in danger of being replaced, or worse.
A cold spring is not an enjoyable experience for farmers who pride themselves on being first to plant wheat in the fall and corn in the spring. During the past few years these courageous planters have been fortunate to get warmer than normal spring weather, but this year it seems that the tables may have turned.
The odds are still in favor of those who plant early, even though the temperatures have been falling into the thirties and rising only into the fifties each day. Both wheat and corn have amazing abilities to tolerate cold, but both of them have their limits. We may need a little refresher course on cold tolerance, so let’s look at some of the information that is out there on the subject.
We suggest to corn producers that the minimum soil temperature at 8AM and at a 2 inch depth in the row should be 55 degrees (F) or higher. Some of our northern neighbors are a little more aggressive in saying that 50 degrees is OK. Corn seed germination can begin at temperatures this low or maybe a little lower, but we are getting onto thin ice here so avoid those conditions if at all possible.
Temperature is not the only issue. When the soil becomes saturated, or worse, flooded, all bets are off since soil oxygen is depleted quickly. Oxygen is not available for the respiration process that releases stored energy in the seed that is needed for germination. When this happens, seed may rot, or as we Southerners say, they “sour.” The effect of soil saturation can only be judged by its actual effect on the seed, combined with the quality of the seed. Seed treatment fungicides may help in some cases, but the worst problem is lack of oxygen. The only way to decide about stands in these situations is to wait and see. Even then it’s not easy.
The other situation that many growers are facing is that of cold injury to wheat. This crop is fairly tough, but its cold tolerance is reduced by a few warm days. This has already been seen in fields that experienced a few warm days followed by frost. Leaf tips have been damaged, but so far I have not seen any situations where significant damage has been done. Some who planted in mid-October may now be regretting that decision.
We are however, getting to the point when damage can occur since most fields have already reached or passed the stage we call “internode elongation”, more commonly referred to as “jointing.” After the plants reach the reproductive stage which is indicated by elongation of the top internode and formation of the embryonic head plants are more susceptible to cold injury. At internode elongation wheat can tolerate temperatures of around 25 degrees for short periods like just before dawn on cold mornings. But when it reaches the boot stage 30 degrees is pushing the envelope, especially if the wind is blowing pretty strong and the cold period follows several days of warm weather. There is a little safety factor here, but not much.
Wind is important since it quickly removes any heat being radiated from the ground that might protect wheat in calm air. So, if temperature falls below 30 and the wind is blowing hard you had better go look after a few days, or call one of us to help you since this is a tough call. Hopefully we won’t have to deal with this issue, but this year has been full of tricks so far and it is probably not finished yet.
The worst frosted wheat I have ever seen still produced about 30 percent of its potential yield on secondary heads that pollinated after the freeze. Nature has a way of surviving, but sometimes it’s not pretty and seldom if ever pays the bills.