Wheat Evaluation for Winter Injury

  • Evaluating wheat for winterkill damage is important for making timely management decisions regarding the conditions of the crop.
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  • Winter wheat stands should be evaluated for plant population and individual plant health.
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  • In situations where the wheat stand is thin or weak, a more intense management strategy may be required.
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Wheat Condition

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After cold temperatures this winter, many growers are concerned about injury to winter wheat stands. Leaf injury from cold temperatures while wheat is dormant will generally not affect yield potential, as new early spring growth comes from the crown. Severe plant injury or even plant death is influenced by wide changes in soil temperature, and multiple cycles of such temperature fluctuations can further elevate the potential risk of damage. Moist soil is not as vulnerable to temperature fluctuations as dry soil. The potential for severe wheat injury is higher on dry soils, north facing slopes, and areas under ice.

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Evaluation

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Stand evaluation should focus on plant population and plant health. Winter dormancy breaks at or above a soil temperature of 39° F. Winter wheat stand evaluations can begin after about 10 to 14 days of warm weather. When evaluating the stand, plants per square foot, stand uniformity, and number of tillers should be measured.

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Optimum plant stands for maximizing yield potential is in the range of 23 to 30 plus plants/ft2 (Table 1). Plant stands of roughly 15 to 22 plants/ft2 can return yields close to full yield potential when conditions are ideal. If stands are not too low, winter wheat plants have the ability to help compensate for reductions in plant number by producing more tillers.

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Table 1. Relative Winter Wheat Yield Potential Based on Early Spring Stand Counts

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Plants/ft2 Rating % Yield Potential
> 30 Excellent 100
23 to 30 Very Good 100
15 to 22 Fair to Good 75-95
< 15 Poor <70
Source: Rankin, M. Evaluating and managing winter wheat stands in the spring. University of Wisconsin. http://www.uwex.edu
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A yard stick or tape measure should be used to count the number of plants along a three foot distance at four to five random field locations to determine plant population. Calculate the average number of plants and multiply by 4 and divide by the row width in inches to determine plants/ft2.

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Example: 44 average number of plants x 4 / 7 inches = 25.1 plants/ft2.

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Assessing plant health should be done by digging several plants and observing the roots and crown tissues for a healthy appearance. Healthy roots should be white and without any dark or soft spots while healthy dissected crowns should be white to light green. If the majority of plants appear to be non-healthy, crop destruction may be warranted.

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Management

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If plant stand counts are below 5 to 10 plants/ft2, destroying the wheat stand and planting another crop may be justifiable. Crop options for replanting may be corn, soybean, or sorghum, but always consult with your seed and herbicide consultant to understand any herbicide carryover concerns that may damage the replanted crop.

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In situations where the stand is thin or weak, a more intense management strategy may be needed. Sparse stands will be low yielding and may become weedy, therefore, weed control becomes more important. Nitrogen fertility is also important in supporting existing and encourage new tiller development coming out of winter dormancy. Depending on the amount of nitrogen applied in the fall, an early spring top-dress application near greenup to support tiller development may be considered.

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Seed cost, fuel, crop protection inputs (herbicides, insecticides, fungicides), cost to destroy, and projected wheat yield (if kept) compared to a new crop potential yield and return should be considered if replanting to a new crop. Prior to destroying a wheat crop, the crop insurance company should be contacted to determine options if needed and review your insurance policy.