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Fall — control of Italian ryegrass

If you want to control Italian ryegrass next spring, the time to attack is this fall, research on the weed in Mississippi indicates.

According to Trey Koger, Extension soybean specialist for the state, a fall application of a residual herbicide should be made prior to Italian ryegrass emergence, which typically occurs in late October and early November. Timing of application is still being refined by Koger and weed scientists, but the application certainly must begin by late September to mid-October.

A fall application can be both effective and cost-efficient, says Koger. “Dual is probably our most flexible and consistent option. It does a really good job. You can plant anything behind an application of Dual in the fall — cotton, corn or soybeans.”

Another option, Command, “does an excellent job,” Koger says. “For the money, Canopy EX prior applied in the fall is also a good option because it controls both horseweed and ryegrass. It’s fairly economical, does a good job on ryegrass and an exceptional job on horseweed. Treflan incorporated in the fall works well too. It will bring you about 80 percent control.”

Italian ryegrass has grown from an isolated problem in Mississippi to one that now infests crop fields in the northern two-thirds of the Delta region and much of the northern half of the state. “We’ve seen it on more acres than we ever have before. I wouldn’t be surprised if it is a problem on half a million acres.”

One reason for the explosion of the weed is increasing wheat acres in the state. Wheat plantings rose to as high as 520,000 acres in 2008 before declining to 230,000 acres for 2009. “Anytime you have more wheat, you have more ryegrass,” Koger said. “We also had a very wet spring in 2009 and we tend to see more ryegrass after a wet spring. Because of the wet spring, we were late on a lot of our burndown applications and ryegrass got big before we started noticing it on a lot of acres. That magnified the problem. We have a higher seed bank of ryegrass than we’ve had in a while.”

Glyphosate-resistant Italian ryegrass was first documented in Mississippi in 2005. But not all of this season’s troublesome populations are necessarily resistant, according to Koger. “We’re working on confirming the number of populations that are for sure resistant. What we can say is that ryegrass has always been difficult to control with glyphosate.”

Italian ryegrass in Mississippi also has documented resistance to ALS herbicides. However, ALS resistance has so far been documented only on roadsides.

The clumpy growth pattern of Italian ryegrass can affect crop stands and the ability of a conventional planter to cut through the residue, even if the ryegrass has been killed. “It’s imperative that fields are clean at planting,” Koger said.

Fall residuals are the most consistent treatment, but there are options for control — albeit more expensive — in the spring, Koger noted. “The most heavily used option in the spring burndown is to add Select or clethadim to Roundup, or coming back with Select if you notice that Roundup did not control the ryegrass. With soybeans and cotton, you can use that all the way into the season. But the bigger you let the ryegrass become, the more inconsistent the control. Select is decent on headed out ryegrass, but it takes a while to control and it doesn’t die completely, and there are restrictions on applying it on corn acres.

“Another option is a February application of Gramoxone. The problem is that we have a lot of other weeds come up between then and planting, which means the producer may have to come back and spray again or put a residual in with the Gramoxone to get you from there to planting.”

Italian ryegrass (Lolium multiflorum) is often confused with perennial ryegrass and was recently reclassified as a sub-species of perennial ryegrass. The most identifying characteristic is the waxy undersides of the leaves. It also has auricles (appendages) at the collar. The auricles are relatively uncommon in grass species.

Italian ryegrass is used as a cover crop on roadsides for reclamation of those areas, and is also used as a forage. It can at times escape cultivation and become established as a weed. It thrives on fertile soils and mild climates.

It has a low tolerance for hot and dry climates and harsh climates during the winter. The Mississippi Delta during the wintertime provides a nearly perfect environment for Italian ryegrass.

It begins emerging in the fall, usually when temperatures are consistently below 90 degrees. Peak emergence occurs in the fall, but you will also see emergence throughout the winter and sometimes into the spring.

It’s classified as a winter annual, but often behaves as a biennial or a short-lived perennial that grows vigorously during the fall and can also grow through the winter and early spring. If conditions are right, it will continue to grow through the summer. It cross-pollinates openly creating hybrids across species of Lolium and it propagates exclusively by seeds.


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