Clean seedbed essential for weed control in winter wheat
WEST LAFAYETTE, Ind. —The most important thing farmers can do to control weeds in the 2011 wheat crop is to provide a clean, weed-free seedbed before planting, Purdue Extension weed scientist Bill Johnson says.
Few herbicides are available for wheat, so getting rid of weeds before the seed hits the ground will help eliminate crop injury and problems with yields.
"If wheat seedlings are emerging and they are competing with standing, live weeds in the fall, we run the risk of wheat not tillering," Johnson said. "If wheat doesn't tiller as well in the fall, we will have fewer plants in the spring to crowd out other weeds and ultimately fewer grain heads for production."
Minimizing or eliminating the competition from weeds in the fall will give wheat the chance to take up moisture and soil nutrients and to absorb as much sunlight as possible, Johnson said.
In addition to a clean seedbed, Johnson said wheat farmers should wait to plant wheat until after the average Hessian fly-free date for their area.
"Planting after the Hessian fly-free date is a good rule of thumb for planting wheat because it also minimizes weed interference," Johnson said. "If farmers can have a weed-free seedbed by that date, or a little bit later, they've probably done a pretty good job of controlling all of the weeds that are going to emerge in that season, and weed emergence after that time will be fairly minimal."
A map of Indiana's Hessian fly-free dates by region is available on the Purdue Field Crops Integrated Pest Management page at https://extension.entm.purdue.edu/fieldcropsipm/insects/hessianfly.php
Should farmers encounter weed problems after planting, Johnson said there are some post-emergence herbicides safe for use in wheat. Glyphosate and gramoxone will control most of the winter annuals, including henbit, chickweed and purple dead nettle.
One common herbicide not recommended for wheat in the fall is 2, 4-D because it can injure crops and create problems with stand establishment and seed head formation.
Another weed commonly found in Indiana wheat fields is wild garlic, which can create a special problem if not controlled properly.
"Our threshold for wild garlic is very low — one plant per field — because the garlic can be harvested with the wheat in the spring and it will leave a flavor with the wheat," Johnson said. "Consumers don't want garlic bread unless they actually are buying garlic bread."
Farmers can try to control garlic by starting with a clean seedbed, and then scouting the wheat fields very soon after the crop emerges in the fall, Johnson said. There are herbicide treatments to control small garlic plants.
Controlling weeds in wheat is essential because waiting until spring means weeds are better established and, because of colder temperatures, less susceptible to herbicides.
A more extensive list of weeds affecting wheat crops in Indiana and Ohio, and herbicides approved to control them, is available in the 2010 Weed Control Guide for Indiana and Ohio at https://www.btny.purdue.edu/Pubs/ws/ws-16/
Writer: Jennifer Stewart, 765-494-6682, firstname.lastname@example.org
Source: Bill Johnson, 765-494-4656, email@example.com