Evaluate winter wheat stands after green up for yield potential based on a stand count and assessment of weed pressure. Laura Lindsay, OSU Extension small grain and soybean production specialist, recommends doing the stand count evaluation after wheat fields are completely green from 10-14 days of warmer temperature. Typically, winter wheat is said to break dormancy once soil temperature has warmed to 39 F or higher. Stand evaluations tend to be more accurate when they are made during weather conditions that are promoting wheat growth.
Small grains can compensate for reduced stands. A 100% stand is not needed to achieve maximum yield potential. Some reduction in plant population is acceptable. While 30-35 plants per square foot is considered ideal, yield potential does not drop below 100% until there are less than 25 plants per square foot. From an economic standpoint, 15 plants per square foot, representing a potential yield of 75%, is the threshold number typically used to make a stand decision. Keep the stand at 15 and more plants per square foot and replant to another crop if it is below that number. In order to get a reliable average upon which to base a decision, check 10 to 15 random areas within the field for every 25-30 acres. The number of tillers in a square foot is equal to the number of tillers in 19.2 inches of row in wheat planted in 7.5-inch rows or 9.6 inches of row for wheat planted in 15-inch rows.
One factor that can modify the decision regarding a marginal stand is straw as a secondary crop. Some farms will keep a lower yield potential wheat crop because they need the straw for livestock bedding. In other cases, wheat straw prices have been very high the past couple of years and can supplement income from a lower grain yield, resulting in a positive economic return. However, any time that yield potential is lower as a result of fewer plants per square foot, the grower should also consider the potential for weed issues.
Once the grower has decided to keep a wheat stand, the next management decision is to determine if some form of weed control is needed. Weeds of concern include winter annual weeds such as purple deadnettle, henbit, and chickweed, plus other problem weeds like wild garlic/onion, dandelion and Canada thistle. Scout at least 10 random spots per 30 acres. In each spot, evaluate a 10 foot by 10-foot area. If weeds cover more than 5% of areas scouted, an herbicide application is probably justified. Another way to evaluate weed pressure is to use a 1-foot square. Pick random locations across the field, toss the square and count the weeds in the square. If the field averages at least 1 broadleaf and/or 3 grass weeds per square foot, consider an herbicide application. In some fields there may be patches of weeds that need to be controlled while the rest of the field does not need an herbicide application. This is another benefit of scouting. The Ohio, Indiana and Illinois Weed Control Guide has a good section on weed management strategies in small grains, including specific herbicides. Herbicides are rated by their effectiveness in controlling either winter annual, summer annual or perennial weeds. That weed control guide bulletin is available to purchase at your local extension office.
Nitrogen fertilizer is an important component to wheat yield. After wheat has greened up, apply nitrogen any time the field is fit for application equipment. Nitrogen can be applied up until growth stage Feekes 7, which is two visible nodes on the wheat plant. The Tri-State Fertilizer Recommendation bulletin provides nitrogen recommendations based on wheat yield goal using the formula 40 + (1.75 x (yield goal-50)). For a 65-bushel yield goal, 66 pounds of N/acre is recommended. Yield goals of 75, 85 and 95 bushels/acre recommend 84, 100 and 115 pounds of N per acre. Any nitrogen that was applied in the fall at planting are subtracted from these total nitrogen recommendations.
There has been quite a bit of research done in Ohio using livestock manure as a spring top-dress fertilizer on wheat. Specifically, the research has been done with liquid manure. The key to using manure is to know the nutrient analysis of the manure. Nitrogen in manure is generally in two forms: a readily available ammonia portion and a mineralizable, organic portion. For wheat nitrogen needs, only that readily available ammonia portion is counted on.
When using manure, account for the phosphorus that will be applied along with the nitrogen. Do not apply more phosphorus than the wheat crop is expected to use. The OSU research work showed that manure nitrogen efficiency was increased when the manure was incorporated with a toolbar that shallowly opened the soil. Even though there was some disruption to the growing wheat, by harvest there was no difference between the manured and commercial fertilizer plots.
Frank Becker is an OSU Extension Agriculture and Natural Resources Program Assistant and IPM Program Coordinator. He may be reached at 330-264-8722.
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