ISSUE 10   July 6, 2006


Rainfall has been far less than average for most of the state this growing season. In fact, for many locations the May-June precipitation is less than half the long term average for this period. Drought stress in crops is reported to be most problematic in the south central region of the state. Some farmers have already cut their small grains for hay and others are considering whether or not to do so. Before haying or grazing your small grain crop, make sure you obtain a release from your insurer, if the crop was insured. Also test the crop for nitrate levels. Cereal crops can be an excellent source of hay/forages. However, during periods of stress, they can accumulate nitrate in concentrations that can be toxic to livestock. Making hay will not reduce the nitrate level in the foliage. You might also consider the following questions before deciding whether or not to hay your drought-stricken small grain crop:

1. What is the current level of drought stress in the crop? Drought stress induces the stomata to close, increasing the temperature of the leaf and reducing the rate of photosynthesis. The first visual symptoms of stress are curling of the leaves and the darkening of leaf color and are most obvious during the hottest part of the day. As stress become more severe, the leaves begin firing, usually from the bottom first. Firing and curling of the leaves reduce the effective leaf area, further reducing the production of photosynthates that will be available for plant growth. Generally, if 50% of the normal leaf area is present, the plant has the potential to continue to grow.

2. What is the current growth stage of the crop? A given level of drought stress is most severe just prior to and just after flowering. If the crop is well into grain filling, there is a good chance that kernels will continue to fill, though they could be shrunken and have low test weight at harvest. If on the other hand, the crop has just flowered and the effective leaf area of the plant has already been reduced to less than 50%, there is a good chance that kernels will abort and there will be little or no grain production even if there is relief from drought stress.

3. What is the likelihood of relief from drought in the near future? From a quick look at the weather forecast this morning (Wednesday) it unfortunately appears that it will be several days before there will be any appreciable chance of rain. Though green and curled leaves can be revived after a good rainfall, leaf tissue that is yellowed or necrotic will not be restored to functionality. When trying to envision what your crop will look like before the next predicted rain arrives, bear in mind that the rate of drought-stress induced damage to the plant will likely increase since soil reserves of moisture are less available. Hot and dry days will be more damaging than if they are cool and humid.

Joel K. Ransom
Extension Agronomist - Cereal Crops

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