Italian Ryegrass Moves the Burndown Bullseye
It might still be winter, but it’s not too early to be applying burndown herbicides to control Italian ryegrass.
A problem in Mississippi crops for years, glyphosate-resistant Italian ryegrass has been moving into Arkansas and West Tennessee, potentially reducing cotton and corn yields in those states by 10% to 20%.
It remains a challenge for Mississippi growers because not only is Italian ryegrass resistant to glyphosate, it’s becoming increasingly difficult to kill with other herbicides. Spraying those now can also be problematic.
“This time of year, I’m talking to farmers about killing ryegrass,” says Dr. Jason Bond, Weed Scientist with Mississippi State University’s Delta Research and Extension Center. “They need to be doing that right now. Most of the time from October to March my conversations fall around controlling ryegrass.”
What Works in Mississippi
With glyphosate resistance so prevalent, “we have two products — clethodim and paraquat — that will work on it, but not necessarily kill it, after it comes out of the ground,” notes Bond. “Both carry a lot of baggage. Clethodim is usually our first treatment, and we have clethodim resistance in Mississippi. But we also have clethodim failures not caused by resistance.”
In a perfect world, clethodim will control 90% of Italian ryegrass.
“The label says an application of clethodim should be targeted at 2- to 6-inch plants before they start tillering or producing seed heads,” he says. “This year it was so dry through the fall, but, often, we get 2- to 6-inch plants in October.
“Spraying in January and February, we’re certainly beyond the target size on the label. So, you take that hypothetical control ceiling of 90% and you’re at 80%. If the application gets made at 35o F instead of 55o F, that takes 80% control to 70%. Maybe it’s a little bit waterlogged, and that takes 70% to 60%.”
Bond says farmers have moved to paraquat-based treatments because of those problems, but “with paraquat in January and February, it has to be just right to give you the maximum that it has. Water volume, temperatures, and sunlight all factor in, and we don’t have all of that this time of year.”
For next year, growers should apply residual herbicides in the fall to keep ryegrass from emerging. “Because of the baggage these two postemergence treatments have, we’ve always stepped back and promoted the fall residual applications.”
In West Tennessee
Ryegrass was an issue in West Tennessee last spring and appears to be increasing, reports Dr. Larry Steckel, Extension Weed Specialist with the West Tennessee AgResearch and Education Center. If it can’t be controlled before corn planting begins in March, farmers have few options.
“The Roundup-dicamba tank mixes we’ve been using for burndown are not cutting it on ryegrass,” he says. “Some of it is due to the glyphosate resistance and some to the dicamba antagonizing the glyphosate. The ryegrass is allelopathic to other grasses and gets first dibs on the nitrogen. A lot of my farmers didn’t control it early in corn, and it really hurt them. They have more time on cotton, but it can still be a problem.”
Steckel said the best option is clethodim 30 to 40 days ahead of planting. “You really need a pint of a two-pound clethodim,” he suggests. “It gets confusing because there are three formulations. Closer to planting, one option is glyphosate and Verdict or Sharpen with 40 to 44 ounces of Roundup. The other is two shots of Gramoxone a week to 10 days apart.”
In cotton, growers should avoid tank-mixing glyphosate and dicamba.
“A lot of times I’ll tank mix clethodim with Roundup to enhance the ryegrass burndown,” says Steckel says. “But it’s not just ryegrass in cotton, we’re also having problems with goosegrass with that Roundup-dicamba application.”
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