Warm-Season Weed Management in Winter Wheat
April 6, 2007
Early spring germinating weeds such as kochia, slimleaf and common lambsquarters, Russian thistle, common sunflower, etc., are tall growing weeds that are generally not affected by wheat stands. However, taller varieties have less of a problem with these weeds than medium and shorter varieties. Scattered early germinating weeds, if not controlled, will grow taller in shorter varieties and may cause problems at harvest, necessitating a harvest-aid herbicide.
Late germinating summer annual weeds can be a problem in wheat fields that have poor wheat stands. However, some weeds, like wild buckwheat, can be a problem even in good stands of wheat. Since it is a vine, it grows up the wheat plants and causes yield loss and harvest problems. Timing is important for controlling wild buckwheat and wild vetch. Apply herbicides later than optimum for winter annual weeds but before the wheat canopy covers the ground. Best results are obtained after these weeds have germinated and before the wheat in in the joint stage. With the increase in plantings of semi-dwarf wheat, we've seen an increase in the amount of wheat acres treated with herbicides. Shorter winter wheat varieties are not as competitive with weeds as taller varieties.
If a grower is going to spray wheat stubble after harvest for ecofallow, many problems can be reduced by controlling broadleaf weeds in spring with a herbicide. Kochia, slimleaf lambsquarters, Russian thistle and common sunflower are the tall weeds that may interfere with harvest and intercept the herbicide before it reaches smaller weeds after harvest. Also, if they are cut off, little leaf area is available to intercept the herbicide for control.
Growers can reduce herbicide inputs by scouting their fields and identifying areas needing treatment. Surveys taken after winter wheat harvest have shown that some fields had a poor stand of winter wheat in certain areas of the field. These areas include waterways, hilltops, or areas where the snow had blown off the fields. Wheat stands in these areas generally had fewer than 280 stems persquare yard at harvest. These areas should be sprayed with a herbicide so that competition from weeds is reduced.
Planting an adapted winter wheat at the proper time improves the wheat's ability to compete with weeds. Apply fertilizer during the prewheat-fallow period or as a starter when the wheat is planted. Delaying all the fertilizer application until spring gives the weeds an advantage. Surveys have shown that fields only receiving spring-applied fertilizer have more and bigger weeds than fields fertilized the previous summer or fall.
Sometimes, wheat fields have questionable stands that may need to be destroyed and planted to another crop. If you are unsure as to what to do, spray the field with a selective herbicide that allows flexible recropping. This lets you decide later whether to destroy the field and plant another crop. The wheat must be destroyed early enough so as not to lose the stored soil water if a spring crop is to be planted.
For more information on weed management see the latest UNL Weed Management Guide for Nebraska (EC130), available online or at your local county extension office.
Robert Klein
Extension Crops Specialist
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