Control weeds, volunteer wheat after harvest

click image to zoomGood precipitation earlier this summer allowed weeds to get a strong start in wheat. To conserve water for the next crop and prevent weed seed production, these weeds need to be controlled within 15 to 30 days of harvest. It's essential that volunteer wheat be controlled at least two weeks prior to emergence of the next crop to break the "green bridge" to disease development. Less than perfect wheat stands this past spring and ample spring and early summer precipitation allowed weeds to get established in many winter wheat fields. These weeds have flourished after wheat harvest. Additionally, hail storms were common in western Nebraska near harvest and volunteer wheat is abundant in many stubble fields.

Volunteer wheat serves as a “green bridge” to carry wheat curl mites, which carry wheat streak mosaic, High Plains disease, and Triticum mosaic virus, to the next wheat crop. Controlling weeds and volunteer wheat is critical to having successful crops in 2012.

Controlling Grasses and Broadleaves

Weeds growing in wheat stubble after wheat harvest use water that is best saved for the 2012 crop, be it corn, sorghum, sunflower, proso millet, or wheat. If allowed to go to seed, these weeds also pose problems for subsequent crops. The general rule of thumb is to wait 15 to 30 days after harvest to spray wheat stubble as part of a three-year rotation that includes a summer crop following winter wheat.

The key is to allow the weeds to recover some from being cut off at harvest, while not allowing so much growth that weeds become difficult to control with herbicides. As with all weed control, it’s essential that you closely watch for weed development and spray at the proper time to achieve maximum control. Most herbicide labels state that weeds must be treated before they are six inches tall. If weeds are under severe drought stress, wait for rain and spray a week later.

Glyphosate is the most commonly used herbicide for weed control in wheat stubble. Some glyphosate products include sufficient surfactant while many products require more. Be sure to check the product label. For all glyphosate brands, add ammonium sulfate (spray grade) at 17 lb per 100 gallons of spray solution. Glyphosate usually provides excellent control of grass weeds, if they are actively growing, but the control of broadleaf weeds can vary widely depending on species, size, and rate of growth. Adding 2,4-D with the glyphosate will help control broadleaf weeds. If temperatures are above 80^oF, use the amine formulation of 2,4-D to reduce the risk of vapor drift to nearby crops. For additional information, treatments, and rates go to the Ecofarming Section (page 25) of the 2011 Guide for Weed Management.