Hartzler on 2015 weed control
OKOBOJI – Weed resistance is not a new issue in agriculture, but it has become a much larger problem with the evolved, widespread and increasing issues of resistance to glyphosate in waterhemp, giant ragweed, marestail and horseweed.
Bob Hartzler, an Iowa State University Extension weed specialist, told producers at the Jan. 7 Crop Advantage meeting in Okoboji that they need to be vigilant in knowing how to protect yields, manage weed seedbanks and preserve the effectiveness of the tools they have to control weeds.
Hartzler said that while he disagrees with the notion that, “one year’s seed is seven years weeds,” he did say there are a small handful of seeds that might last seven years, but most are there only a year or two.
“The larger the seed bank size, the lower the herbicide effectiveness,” he said. “And with that, resistance risk goes up.
“If you maintain a complacent attitude about weed control, it will create a lot of problems.”
Hartzler said one of the most effective weed control options available to producers is getting that crop to canopy as soon as possible. If weed seeds can’t be easily fed through water and sunlight, photosynthesis cannot take place effectively and weed seeds are less likely to grow.
Hartzler said the new herbicide-resistant crops are not the next silver bullet, saying their advantages include application timing and crop safety, but the concerns include off-target injury and resistance complacency.
He said identifying resistances existing in specific fields is an important first step in determining what weed control measures to take, along with knowing the history of weed control attempts in each field.
Hartzler said producers should work to have an understanding of herbicide group numbers and how to use them to their best advantage-both financially and effectively.
Hartzler recommended using multiple effective herbicide groups for each application and said that combinations are more effective than the rotation of herbicide groups.
Producers should also recognize the need to use the highest herbicide rate available for the crop and soil type, he said.
Understanding herbicide group numbers is important, he said, in determining if a multiple-component mixture includes herbicides that are both effective on specific weeds and not just for one of the weeds targeted.
“In many cases, one or more of the component herbicides are no longer effective for the target weed due to pre-existing resistances,” Hartzler said.
Hartzler said if glyphosate is a component of a herbicide pre-mixture, there is a high likelihood that it will not be effective on waterhemp.
Under those circumstances, he said there is no herbicide diversity since only one of the herbicides is effective on the waterhemp, which can result in selection for an additional resistance to that herbicide.”
Hartzler said another concern for herbicide pre-mixtures is that the rate is often reduced since it’s placed with another herbicide, rather than if the herbicide was applied alone.
He said effective weed management calls for full rate application of herbicides.
Hartzler said biological weed control measures such as cultivation and cover crops can help reduce weeds, but it’s not the best plan for weed management.
The more diverse the tactics used for weed management, the more positive impact it will have on herbicide-resistant weeds, and economic success will be greater, he said.
Problems relating to herbicide resistant weeds has prompted the need for new weed management tools.
Hartzler said the industry has looked to altering crops to offer new herbicide options, though he said they should be viewed as short-term fixes and that they need to be managed in ways to minimize the risk of continued resistance.
Briefly, he said the Enlist trait provides resistance to 2,4-D and has been placed into corn, soybeans and cotton. Enlist corn will be resistant to 2,4-D, glyphosate and the FOP chemical family (which blocks an enzyme that help form lipids in the roots of plants).
Enlist soybeans will be resistant to 2,4-D, glyphosate and glufosinate. He said the U.S. Department of Agriculture has deregulated the trait, but Dow-AgroSciences is intending to wait until the trait receives approval in foreign markets before launching the product.
Hartzler said although the trait provides some cross-resistance to certain Group 4 herbicides, there is little effect on soybean sensitivity to dicamba.
Producers should be sure to read the label to know the restrictions associated with it, including wind speeds, buffer zones and the use of specific sprayer nozzles.
Hartzler said Monsanto’s approval of Roundup Ready Extend soybeans is still under evaluation by USDA. Soybeans with this trait will be resistant to glyphosate and dicamba. Both Monsanto and BASF are developing dicamba formulations that will have lower volatility than current dicamba products.
He said Monsanto will introduce Roundup Xtend, a combination of dicamba and glyphosate.
He said Balance GT soybeans were deregulated by the USDA in 2013, but commercial release will not occur until 2016. Balance GT soybeans are resistant to isoxaflutole and glyphosate.
MGI soybeans will have resistance to mesotrione (Callisto), glufosinate (Liberty) and isoxaflutole (Balance).
Earliest availability will most likely happen in 2016, Hartzler said, since applications for its approval have been submitted to USDA.
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