Some producers attending this year’s Milan No-Till Crop Production field day told University of Tennessee weed scientist Larry Steckel that the target date of 2013 for commercialization of dicamba-resistant soybeans just isn’t soon enough.
But Steckel, who has been studying the technology for two years, says dicamba beans and producers will benefit from a few more years of research. “There are a lot of questions yet to answer, like what tank mix partners we can use.”
The technology, developed by Monsanto, will allow for the application of Roundup and dicamba over-the-top of soybeans. Currently dicamba is used for burndown to control glyphosate-resistant horseweed in a number of Mid-South crops.
“The primary benefit of the technology is to help with weeds that farmers are currently struggling with,” Steckel said. “Those include morningglories and a lot of the glyphosate-resistant weeds that are becoming more and more of a challenge. It looks like it’s going to be a good fit for giant ragweed and it could be a fit on glyphosate-resistant Palmer pigweed.”
One concern in current research is keeping dicamba where it’s applied, Steckel says. “It’s very volatile like 2,4-D. Even if you do everything right, drift can occur.” For example, in July, Steckel sprayed dicamba-resistant soybean plots at 8:30 in the morning with zero wind. But a temperature inversion trapped the spray near the ground. Later, temperatures increased, and as the dicamba rose from the ground, a slight breeze blew it to a nearby plot of Roundup Ready soybeans, injuring them.
“The big question is will we lose yield on that. It depends on the year. If we have some rain, probably not. If it’s really dry, we could.”
Monsanto and other companies are working with different formulations of dicamba to address the drift situation, Steckel said.
Early research also indicates the sequence of application is crucial to control of resistant marestail. “We went with 8 ounces of dicamba and 22 ounces of Roundup WeatherMax followed 10 days later with Roundup at 22 ounces. With that treatment, we got complete control. But when we went out with straight Roundup at 22 ounces followed 10 days later by dicamba at 8 ounces and Roundup at 22 ounces, we got almost no control.
“In the second scenario, the marestail is resistant, but it’s not completely bulletproof to the first application of Roundup. Roundup injures it just to the point where it doesn’t take up followup herbicides.”
Currently in the Mid-South, there are five glyphosate-resistant weeds — giant ragweed, common ragweed, Palmer pigweed, horseweed (marestail) and johnsongrass. Steckel noted that dicamba has very good activity on four of them (the exception is johnsongrass). “I think it’s going to bring a lot to the table.”
Steckel added that Southeast studies indicate that dicamba on 3-inch to 4-inch tall glyphosate-resistant Palmer pigweed provided good control. But it’s not as effective when Palmer pigweed is taller.
Dicamba can also address problems with redvines in soybeans during the season, according to Steckel. “Right now, all I can tell farmers is to spray as much dicamba as you can after harvest. That’s about the only thing we can do.”
Another weed control product, from Bayer CropScience, LibertyLink soybeans, is expected to have enough seed to plant 250,000 to 300,000 acres in the Mid-South in 2009. Ignite herbicide can be sprayed over-the-top of LibertyLink soybeans at 22 ounces to 29 ounces per acre, with a season limit of 44 ounces.
“Bayer is trying to get the limit up to 66 ounces,” Steckel said, “so producers could go out with three 22-ounce applications.”
Currently, there is a very limited variety selection, but from what I’ve been told, yields look pretty good.
Steckel says Ignite is excellent on morningglories, glyphosate-resistant horseweed if it’s warm and glyphosate-resistant giant ragweed. “Ignite will do a pretty good job on Palmer pigweed that’s 3 inches tall. In general, it’s weaker on grasses, particularly johnsongrass and goosegrass. It’s not going to be a standalone treatment. It will require a pre-emergent and postemergent treatment or sequential post treatments to get the control we need in a lot of cases.”
The bottom line is that producers in the Mid-South “are going to have to rethink their weed control programs,” Steckel said. “I’ve seen a lot of glyphosate-resistant soybean fields that got pretty big before growers decided to spray glyphosate on them. If you wait too long with Ignite, you’ll have a problem. It will burn the tops of 12-inch tall Palmer pigweed, and they will come back. So timing is going to be critical.”
In the early 2000s, “weed control was as easy as it will ever be,” Steckel said. “From now on, it’s going to be much more complex. These new technologies are going to help us with glyphosate-resistant weeds, but they have issues themselves and most have to do with timing. You have to put them out early.”
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