By Roger Don Gribble
`Wheat producers are evaluating their stands and determining future plans for the 2013 harvested wheat crop.
It is dry in most locations, and in a few areas, wheat has yet to emerge. What also is emerging are some annual grassy weeds in the crop. Cheat, ryegrass, rescuegrass, downy brome, rye and jointed goatgrass have emerged and are off and running ahead of wheat.
Depending on where you are standing in northwest and north central Oklahoma, the weed species will be different. There seems to be more jointed goatgrass west and north of Enid and more rescuegrass to the west and south of Enid. For everyone else, by far and away, downy brome seems to be the species of highest density.
Over time, herbicides such as Olympus, Olympus Flex, PowerFlex, Finesse Grass and Broadleaf, Maverick and Beyond have done an excellent job of controlling cheat, but have been weak on downy brome control. Most of herbicides have been applied in the spring with a topdress application of nitrogen.
In the spring, we have limited success with trying to control downy brome, so producers have allowed downy brome to become a much more populated weed in wheat. Downy brome matures much earlier than our other weedy grasses and will shatter more seed onto the ground, so rarely would producers receive a dockage figure at harvest.
There are a couple of suggestions that could be made to reduce the yield loss to downy brome. The first would be the use of crop rotations. The work done at the North Central Research Station at Lahoma indicates less grassy weeds where the three-crops-in-two-years rotations have been implemented.
It seems with herbicides used in either the summer crop rotation or as the rotation moves to the double crop behind wheat, there is a reduction in the downy brome species. When the rotation moves back to wheat, we have not needed a weed control product for downy brome. These experiments are working with a no-tillage system, but tillage also is an excellent option for controlling downy brome.
A second option and more targeted to producers in continuous wheat production would be the herbicide technologies currently used. The slight adjustment would be to move that herbicide application into the fall rather than the traditional spring season. This holds true with our usual cheat control products mentioned earlier.
Not only is our cheat control better in fall applications, but our downy brome control also is greatly improved. Not always, but usually we see an improved yield from wheat when weed competition is reduced with the fall herbicide applications.
As always, weed control of grassy weeds are better when both wheat and weeds are actively growing.
At the time of this writing, our weather conditions are not very good. I am looking at an improved rainfall chance earlier next week, so there could be an opportunity to control weeds yet this fall.
Please contact your Oklahoma Cooperative Extension Service ag educator in your county for additional information on weed control in wheat.
Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.