AgWatch


Specialist Offers Ways To Curb Resistant Chickweed In Wheat

BETTY VALLE GEGG-NAEGER
MidAmerica Farmer Grower

PRINCETON, KY.
   Problems with controlling common chickweed, are showing up in some Kentucky wheat fields, according to Dr. Jim Martin, extension weed scientist with the University of Kentucky.
   “Common chickweed is not necessarily a new weed in itself, but ALS resistant common chickweed is becoming a problem in wheat fields in Kentucky,” he said. “This type of resistance is not new, it was first reported in 2006 in Virginia; then within a year or two it appeared in Delaware and Maryland. Now it’s in Pennsylvania and possibly in North Carolina. I guess we can put Kentucky in that list as well. We have some fields especially along the southern tier counties of Kentucky where we grow a lot of our wheat where this resistance is showing up.”
   Concerning ALS resistance, herbicides like Harmony or Harmony Extra, Finesse, and Express are products used for managing common chickweed. That group of chemistry is very prone to developing resistance and it showed up soon after the Sulfonylureas were developed in the early 1980s. It took about two to four years out in the Great Plains where they grow wheat after wheat and there’s little or no rotation for resistance to show up in those environments.
   “So circumstances in the Great Plains were ideal for developing resistance to this unbelievably good chemistry for weed control,” Martin said.
   “I feel crop rotation has played a key role in limiting the spread of ALS resistance in wheat in Kentucky. We often plant wheat in the fall after corn harvest and then follow up with soybeans after wheat harvest the next season. This system of three crops over a period of two years allows growers to use different herbicide chemistries. Also, the use of a burndown herbicide program in early spring prior to planting no-till corn often limits production of chickweed seed by killing plants before most of them flower.










   Common chickweed is not a new weed in
   itself but Dr. Jim Martin, extension weed
   scientist with the University of Kentucky,
   says problems with controlling it are
   showing up in some Kentucky wheat fields.

   Photo by John LaRose, Jr.











   “Unfortunately, ALS resistant chickweed is showing up, even in some of these situations where rotations are used. That system is not always perfect. Mother nature is in control.
   “We’re currently evaluating herbicide options for managing this weed in wheat,” he continued. “Our Kentucky Small Grain Growers Association has been supporting this project. We identified a field over in Christian county and we did some applications in the fall of last year and in the spring. I think the message that we have thus far is there are some options out there. Fall applications are probably going to be the best approach and, by all means, if we can control chickweed in the fall before it overwinters I think that’s easier. Fewer plants will overwinter and produce seed come next spring.”
   Metribuzin 75 DF applied in the fall at 2 to 4 ounces of product per acre seems to do a good job of managing common chickweed, even the ALS resistant common chickweed. Huskie and Starane Ultra are other options that have chickweed activity.
“However, I really stress, those products in particular really do better if we spray them in the fall before the chickweed overwinters,” said Martin.
   “So the key message is to be timely and spray a herbicide preferably in the fall in the wheat crop itself,” he continued. “I also might add that when we’re in an off year and in other crops, we have to do all we can to keep that chickweed from going to seed. Keep those burndown applications timely, before chickweed goes to seed in a corn rotation. I think that’s a really important asset into managing this problem weed.”
   Metribuzin is one of the key components that has worked well in the fall and in spring applications, but it takes higher rates of metribuzin once the weeds gets some size to them.
   “A concern I have with metribuzins is its potential to injure wheat,” Martin added. “There are varieties that could be susceptible to injury, but varieties change so rapidly that it’s really hard to get a handle on which ones are safe to spray. So because of that unknown we’re really reluctant to use the higher rates. We’re doing what we can, by making those applications earlier when the chickweed is small and easy to control. This also allows us to use the lower rates, which may minimize the risk of injury to the wheat. I’m not saying we won’t injure it, but hopefully, it will lessen the chance of injuring wheat.” ∆
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower
MidAmerica Farm Publications, Inc
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