Fallow wheat ground means chance to reduce ryegrass populations

LITTLE ROCK, Ark. — In October I decided to wait until our wheat research sites received some rain rather than trying to dust in our plots. The three locations where we conduct wheat weed control trials were all dry as a bone back then.

Since then it has rained too many times to count. We were able to plant one site because it is a very sandy soil; if the seed treatment holds up we may get a stand. If we do, I will brag about Delta King’s wheat seed and seed treatment program because it has been so wet.

Our Hoelon-resistant ryegrass location is still too wet to plant, and we are giving up on it.

From what I hear, wheat acres in Arkansas will be down a lot this year due to the weather, low wheat prices, high early-soybean prices and urea costs.

To take advantage of not having plots at the Hoelon-resistant site, we will apply a full rate of Hoelon to the entire site. This will help to insure our population is mostly resistant. This is the worst thing you can do on a commercial field where you are managing Hoelon-resistant ryegrass.

We also are going to spray the entire site with 2,4-D to reduce a growing population of broadleaf weeds. If you have a field that you were not able to put in wheat this year or if you are not planting wheat for some other reason, take the opportunity to reduce your ryegrass problems.

Several years ago, Dick Oliver, my research counterpart in Fayetteville, Ark., had a graduate student project that focused on the effect fallowing a field for one year had on reducing ryegrass populations. What he found was that completely controlling ryegrass with chemicals, tillage, or (best) a combination of chemicals and tillage, could reduce ryegrass populations for about three years. Reductions of ryegrass populations by as much as a 90 percent for the first two years were documented.

Fallowing was less effective at reducing ryegrass in true no-till systems, so some sort of fall or spring tillage is recommended for best results. Fallowing a wheat field gives you the opportunity to hit resistant populations of ryegrass with a herbicide like glyphosate that is in a different family of chemistry from Hoelon. And, like a former advisor used to say, nothing is resistant to cold steel. Fallowing is an excellent resistance management option for Hoelon-resistant acres.

In a fallow rotation, I prefer to control ryegrass chemically in the fall, just before cold weather sets in. Due to the low cost of Roundup and glyphosate-containing products these days, they are natural choices.

We have had good success with 1.5 to 2 pints per acre of glyphosate (4 pounds per gallon) on three- to six-tiller ryegrass in late fall — mostly from spraying alleys in plots and areas that we want to clean up a bit.

I have heard some people say they cannot kill ryegrass with Roundup. That result typically comes from trying to control ryegrass in the spring after the ryegrass has begun panicle initiation. Ryegrass is especially hard to kill after joint movement and is a problem in no-till corn and other crops planted early in the spring. Even tillage can miss some large or dense clumps and patches of ryegrass, so don’t wait too late in the spring to till for control.

We have had good success with glyphosate sprayed on small ryegrass before the reproductive stage. If ryegrass gets larger, we have to move to 1 to 2 quarts per acre.

Our wheat weed control research programs at the University of Arkansas are funded in part by the Arkansas Wheat Promotion Board. Without that support, much of our work would simply not be possible. We greatly appreciate their support.

Bob Scott is the University of Arkansas Extension weed specialist. e-mail: [email protected]