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Wheat Management Decisions

Posted Apr. 1, 1998

This year reminds me a lot of last year. Plant development is ahead of schedule. For those of you who plan to harvest grain from your wheat crop it could be boom (high yield) or bust (freeze damage).

Wheat yield is affected by three yield components: the number of heads per acre, the number of seeds per head, and seed weights within the head. Each develops at a different time period. The number of heads (tiller number) is pretty well set by now. In the Southern Plains, wheat yields are usually highly correlated to that yield component.

If you have a good thick stand, you have the potential for a reasonable grain yield in any year. The second yield component, seeds per head, is set in a short few-week time period after jointing. It is somewhat genetically controlled, but good environmental conditions like we now have can increase the number of seeds per head. Probably the most important yield component in bumper crop years comes from the increase in seed size and test weight resulting from cool, moist environmental conditions during the grain filling period.

Since plant development is so far advanced, the chances that wheat will flower and begin grain fill earlier than normal are high. In the really high yield (100-200 bu/acre) regions of the world - the Pacific Northwest or northern Europe - grain filling usually lasts from six to eight weeks resulting in much larger seeds than we normally see. In the Southern Plains grain filling usually lasts about one month under normal heading dates.

Years like this present a real dilemma for wheat producers. With early heading like we encountered last year, the danger lies in the potential for a freeze to badly damage the wheat crop. For those of you whose wheat had just headed when the hard freeze occurred last year, you were probably very disappointed with your yields or were wiped out completely. For those whose wheat escaped because it was protected "in the boot," you saw cool, moist conditions during May and early June giving an extra one to two weeks for grain fill. Your yields were probably much higher than you expected as a result.

We're set up for that same possibility again. On the down side, the likelihood that a late freeze could damage the wheat crop increases. If you're really concerned about that, consider grazeout as an option. If you've already made your plans for grain, observe plant development carefully so you can take advantage of what could be a bumper crop.

Because the winter has been so mild, the potential for serious foliar diseases also rises. However, wheat experts in the Southern Plains have not found much leaf rust or Septoria leaf blotch as of this writing.

Wheat is currently pretty cheap, so you may be thinking, "Let's not waste any fungicide on a crop that isn't worth much anyway." Look to those situations where you would get the best return. That would be on susceptible varieties like Karl, Karl 92, Chisholm, Cimarron and TAM110 and in situations where you have a higher market value.

Seed production would fall into the latter category. If you save your own seed, consider a fungicide application for the fields from which you plan to keep your seed. If we get past heading without freeze damage, fields protected with fungicide might respond very well. Tilt, the logical fungicide of choice, must be applied as the flag leaf emerges (Feekes growth stage 8). That will occur very soon, so scout your fields to determine if diseases are present at treatable levels.

Keep in mind, this is written in early March on a subject that's four to six weeks in the future. Begin thinking about your yield potential and go to the field to observe plant and disease development. While it's too early to tell whether this year will be "boom" or "bust," these management considerations might help preserve your yield potential if it turns into a bumper crop.

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