The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.
QUIK STATS (last updated Jan 28, 2014 )
NOTES ABOUT THIS BIOTYPE
ALS– RESISTANT COMMON CHICKWEED IN WHEAT
James R. Martin—Extension Professor of Wheat Science
In 2012, consultants with Wheat Tech reported finding common
chickweed in several fields in Logan, Simpson, and Warren Counties that was not
controlled with ALS inhibitors such as Harmony Extra or Finesse. ALS stands for
Acetolactate Synthase which is an enzyme sys-tem that helps make certain amino
acids in plants. The following photo is an example where an ALS-inhibitor
her-bicide failed to control common chickweed in Kentucky this past season.
In 2008, ALS-resistant common chickweed was discovered in
wheat in Virginia and is now believed to be in Delaware, Maryland, North
Carolina, and Pennsylvania.
The potential impact of this resistance could be significant
to Kentucky wheat growers. ALS-inhibitor herbicides play an important role in
managing chickweed, henbit, and wild garlic in wheat in Kentucky. Harmony and
Harmony Extra (and several generics of these) are applied on about 75% of the
wheat acres in Kentucky.
Since common chickweed is fairly competitive, it is desirable
to control plants when they are small. The majority of common chickweed emerges
in the fall; therefore, fall applications tend to be preferred over spring
applications for controlling this weed in wheat. The activity of ALS inhibitors
tends to be slow, particularly during periods of cool temperatures.
Consequently, it may be several weeks after fall applications before you know
if the treatments were a success or a failure.
ALS-inhibitor herbicides tend to be prone to developing
resistant weeds. The fact Kentucky growers have avoided ALS-resistant common
chickweed in wheat for more than 25 years of widespread use of Harmony and
similar herbicides, is no accident. Our rotation system of three crops over a
two year period (i.e. Wheat / Double-Crop Soybean / Corn) has limited the
development of ALS-resistant common chickweed. Applying burn-down applications
of glyphosate, paraquat, or atrazine prior to corn planting early in the spring
can limit production of common chickweed seed, if applications are applied
before plants produce viable seed. Keep in mind, ALS-inhibitor products used in
burndown appli-cations in corn such as Basis, Basis Blend, Resolve Q, Leadoff,
or Crusher may not control populations of common chickweed that are resistant
to this chemistry.
The Kentucky Small Grain Growers Association recently funded
a the project to confirm this resistance and to evaluate alternative herbicide
CONTRIBUTING WEED SCIENTISTS