Monday, April 11, 2011
No till Beans And Resistant Marestail: A Problem That Can Be Solved
Marestail was not a problem for your Dad. Why is it a problem for you? Since you have switched from mechanical control of weeds to the advanced chemistry of glyphosate, the marestail that could not escape cultivator sweeps has found a way to survive Roundup. That means you have to find a way to outsmart marestail once and for all, and if the field of battle is no-till soybeans, the whistle has blown and its game on!
Increased production of no-till soybeans means greater challenges for controlling marestail, particularly if it is resistant to glyphosate and possible ALS inhibitors. If your goal is to eradicate marestail prior to planting, and also obtain residual control until the soybean canopy can form, Ohio State University weed specialist Mark Loux has a number of recommendations.
Starting with the burndown challenge and assuming you have a glyphosate resistance problem, Loux says don’t use glyphosate alone because it will only allow more weeds to develop resistance. And with marestail resistant to both glyphosate and ALS inhibitors there are a number of herbicides that will not provide either post-emergent control or residual control. Those include a post application of Classic, Synchrony, or FirstRate, and it also includes the burndown products Canopy, ValorXLT, or Authority First. Loux says 2,4-D alone will not control marestail beyond those that have just emerged, nor will combinations of 2,4-D work with residual herbicides Canopy, Sonic, Envive, or Authority First.
So what will work for a burndown?
1. Glyphosate with 2,4-D and AMS will have optimum effectiveness on marestail that is less than 4 in. tall, and if weather conditions are good for plant growth. Use glyphosate at a 1.1 to 1.5 lbs acid equivalent per acre, and 2,4-D at a 0.5 ae/A. Rates higher than that will delay your ability to plant from 7 days to as many as 30 days depending on the product used.
2. Safulfenacil with glyphosate and MSO and AMS can be effective on plants that have survived the winter. If 1 oz of Sharpen is used soybean planting can follow by 7 days, but that extends to 14 days if a 1.5 oz rate is used. Verdict and Optill can also be used, but Sharpen is the least expensive. This premix requires an adjuvant of at least 60% methylated seed oil. Loux says since safulfenacil is a PPO inhibitor, it cannot be used within 30 days of other PPO inhibitor herbicides, such as Spartan or Valor.
3. Ignite 280 and AMS can be used if you are planning on use of a pre-emergent herbicide that contains Valor or Authority. The Ignite 280, which contains glufosinate, can be used for a burndown before planting any type of soybean seed. Loux says the minimum application is 15 gal. per acre or 20 gal. in dense weedy vegetation. It also needs to be applied when weeds are actively growing. If weeds are larger or not actively growing, he recommends the addition of 4 to 6 oz of metribuzin 75DF.
The marestail is burned down now, but how do you get season control?
Mark Loux says do not expect good residual control of marestail with a product that is applied along with a burndown several weeks before soybeans are planted. A good residual product needs to prevent marestail emergence until the soybean canopy can take over. He suggests several points to consider:
1. Is your marestail population also resistant to ALS inhibitors, as well as glyphosate resistant? If FirstRate or Classic did not have any effect, it is probably ALS resistant, but assume that it is ALS resistant and select residual herbicides based on other choices.
2. The most effective choices include both an ALS inhibitor and a non-ALS inhibitor such as Valor, Authority, and metribuzin. Some premixes include Valor XLT, Envive, Sonic, Authority First, Authority XL, and Gangster.
3. Consider the adequacy of the glyphosate rate in premixes, which should be satisfactory if the marestail population is not ALS resistant. But Loux warns, “In ALS-resistant populations that non-ALS component of the premix is providing all of the residual marestail control, and the rate of that component becomes more important. Another way to look at this – Valor will be just as effective as Valor XLT or Envive for control of ALS-resistant marestail, although control of other tough broadleaf weeds may decrease.”
4. If the glyphosate is supplying a low rate of the non-ALS component, it should be increased or supplemented with an additional herbicide to control the ALS resistant marestail.
5. Loux says Sharpen only provides 40% to 70% residual control, and needs the help of additional herbicide. But what can be added to Sharpen, since flumioxazin or sulfentrazone cannot be part of the pre-mix? Loux says Scepter and Pursuit do not control ALS-resistant marestail, but he suggests the combination of Canopy or Cloak DF with metribuzin if the burndown was a tank mix of glyphosate and Sharpen. He says another approach is the use of Ignite for a burndown instead of glyphosate and Sharpen, and that will allow the use of any residual herbicide.
Summary:
With increased acreage of no-till soybeans in an environment where marestail is becoming more tolerant of glyphosate, there will be many challenges to control it. Many populations of marestail are not only resistant to Roundup, but also to other herbicides that are ALS inhibitors. Adequate control, both in burndown and residual control, is achievable, however care must be taken to avoid extending the planting time after an application, and to prevent the addition of herbicides that have similar chemistry.
Posted by Stu Ellis on 04/11 at 12:00 AM | Permalink