Crops
by Dr. Paul Tracy

Walking wheat

Evaluating wheat stands is especially important this year

In March, my mind always drifts toward wheat management. Wheat provides the first opportunity for agronomists to get our feet wet (or muddy) as we jump into a new growing season.

Wheat in our region entered the winter in marginal to poor condition. This was primarily a result of late planting associated with delayed soybean and corn harvests. In some environments when wheat was planted at the optimum time, post-planting conditions caused uneven stands, delayed emergence and poor growing conditions. For these reasons, I expect to see thin, uneven stands as wheat breaks dormancy across our region.

One universal observation was that wheat did not have time for optimum fall growth and development. Most plants initiated few, if any, fall tillers (secondary stems). In our region, there is limited time for tiller development in the spring. Temperature plays the dominant role. When it gets too warm too fast, the window for viable tiller formation is very narrow.

Four major growth factors determine wheat yield. They are number of plants per acre, number of seed heads per plant, number of grains per seed head and weight of individual grains. The number of plants per acre was set last fall. The number of grain per head and grain weight will be set later this spring. The number of viable stems per acre started being set last fall and continues for a few weeks after the crop breaks dormancy. By the jointing stage, new tillers will generally not have enough time to produce viable grain.

Like all annuals, wheat lives solely to produce viable seed. If the environment coming out of winter offers good yield potential, the crop will initiate more spring growth, including new tillers. Conversely, if the plant is experiencing a poor potential production environment, it will conserve its energy for the yield potential it currently possesses.

One way to initiate more spring tillers is to add nitrogen to the system. This will indicate to the wheat plant that nitrogen nutrition is not limiting. In response, wheat will attempt to produce more seed by producing more tillers. Under ideal conditions, especially when fall tiller production is robust, I usually recommend waiting until full green-up for the first spring nitrogen application. By waiting, you can avoid unnecessary nitrogen use on fields that did not survive the winter. Also, nitrogen lying on top of the soil surface, especially under frozen conditions, could be subject to surface run-off loss if excessive rainfall events occur. If you are confident the stand will survive the winter, then applying nitrogen a week or so before green-up is ideal.

Stimulating tillers through early season nitrogen application is especially important this year as so many fields were planted late and did not have time to initiate an optimum number of fall tillers. Nitrogen needed for tiller stimulation must be available as soon as the plant breaks dormancy. Therefore, if you haven’t applied nitrogen yet, now is the time to make that application.

A rule of thumb for making an early spring nitrogen application on wheat is to count viable tillers in the late winter. Stem counts below 100 per square foot indicate a need for nitrogen now. Going into the winter, I observed few, if any wheat fields that would maintain an average 100 stems per square foot. If your stand contains greater than this number, hold off a few weeks before applying nitrogen.

Many producers, especially in the southern parts of our region, prefer to split spring wheat nitrogen applications, using half now and half after jointing. This is a good option for those set up on tramlines, use airplanes, have a planned fungicide/insecticide/herbicide application or who consistently produce wheat yields greater than 80 bushels per acre.

Thin stands this year should provide an ideal environment for weed germination and growth. The key to spring weed control in wheat is to eradicate winter annual weeds early. By the time these weeds flower, it will be too late, and the herbicide application will simply be an act of vengeance.

Dr. Paul Tracy is Director of Agronomy for MFA Incorporated.

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