For Release August 8, 2000

Summer Crop Stress Problems

by Chuck Otte, Geary County Extension Agent

This is Kansas, and sometimes the weather turns off hot and dry. Regardless of what rain we have or havenít had of late and what the rest of the year hands us, there has already been enough heat and drought stress that we are looking at some major problems this fall. Drought stress usually is accompanied by high temperatures, for some reason. So as we talk about drought stress, it will be a combination of below normal rainfall and average or above average temperatures.

In its initial stages, drought stress impacts plants by reducing the amount of water available for the plant. As the moisture runs out, the plant starts to shut down growth in various stages. For a while, it will try to just go dormant and carry on very little photosynthesis or growth. Without some moisture, the plant will eventually use up its existing internal moisture and die.

Short term stress is most damaging to corn. It basically has one shot at producing an ear and a tassel to pollinate it with. Milo can generate new tillers with new heads and soybeans can produce new flowers to set pods when adequate moisture returns. If the moisture arrives early enough in the growing season then the crop will produce near normal production levels. If it comes too late in the summer, the crop is likely to be killed prematurely by frost and the grain will be shrunken and shriveled.

Even with short term stress, though, other problems can start appearing. There are some very common, but rather weak, fungus organisms in the soil. A healthy plant will not be bothered by these fungi. But place the plant under stress for a period of several weeks and problems will start to appear.

The most common fungal disease is called charcoal rot. Charcoal rot is very common and rather undiscriminating. It will attack corn, grain sorghum or soybeans. The pathogen moves into the plant, through the roots, during times of stress. If the stress continues, it attacks the plant in the stalk, right at, and just above, ground level. The time from when the disease starts and you see anything, can be weeks.

The first thing that you might notice is premature death or ripening. Since this shows up most often in dry weather, you may think that the crop has simply run out of water. But a check of the soil may very well show that there is still some moisture present. The disease organism has killed the stalk at the base of the plant. Once the stalk is killed, the grain will dry down regardless of what stage of growth it was in because the roots can no longer get moisture up to the plant.

If you grab one of these plants, they will often fall over at the base. The stem is often easily crushed between your fingers. If you split it open itíll be hollow with just a few fibers left inside and lots of black powdery masses. These plants will lodge very easily as the year progresses making harvest difficult.

We are already finding charcoal rot in all three crops. I strongly recommend you start checking your fields and getting ready to harvest just as soon as the crop is dry enough. For more information, stop by the Extension Office and pick up our bulletins on stalk rots and charcoal rot.


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