A look at your alternative herbicide options
Common chickweed that is resistant to the ALS-inhibitor herbicides is increasing in prevalence in PA and the Northeast. The “Harmony-like ” herbicides are no longer effective for control of this resistant biotype. Other ALS or “Group 2” herbicides used in wheat including Osprey and Powerflex are also ineffective on the resistant biotype. Fortunately, there are some other options that can provide good control of ALS-resistant common chickweed in wheat. Here are some options.
Dow AgroSciences markets Starane Ultra which contains fluroxypyr. Starane Ultra is a plant growth regular herbicide labeled for wheat, barley, and oats. It is applied at 0.3 to 0.4 pints per acre from the 2-leaf crop growth stage up to flag leaf emergence. Fluroxypyr will also suppress horseweed/marestail, and several mustard species, but is not the product of choice for other common winter annuals such as henbit, red deadnettle, etc. Also, Starane Ultra currently has a 120 day recrop restriction to soybeans, so that may also be a consideration. Pulsar is a premixed product from Syngenta that contains the active ingredient in Starane (fluroxypyr) plus dicamba (Clarity). The 12.5 fl oz per acre rate provides the equivalent of 0.26 pt Starane Ultra.
Glory Herbicide (Makhteshim Agan of North America, Inc.) contains 75% metribuzin and has received a “Special Local Need” 24 (c) label for control of ALS-resistant chickweed in winter wheat and winter barely in Pennsylvania. Other brands of metribuzin do not have this special use in Pennsylvania. Specifically, Glory should be applied to winter wheat or barley at 2 to 4 oz/acre after the crop is beyond the 3-tiller stage but before jointing. This is a relatively low rate of metribuzin that is specifically targeting chickweed but it will also suppress other winter annual broadleaves. Some wheat and barley varieties are known to be sensitive to metribuzin and a list of known tolerant varieties is provided on the Glory label. You can find the Glory 24 (c) label at CDMS.net.
Both Starane and Glory may need to be tank-mixed with Harmony Extra or a similar product to broaden the spectrum of control. Finally, two other products worth mentioning are Prowl H2O and Zidua, both from BASF. Both will help control common chickweed and should be applied after wheat shoots are visible (row and go). Emerged weeds are not controlled. For additional information see the Field Crop News article from September 9.
We conducted trials in 2011, 2012, and 2013 in barley or wheat focused on ALS-resistant chickweed control. Here are some of the take home points from our chickweed work:
- Metribuzin and fluroxypyr provided the most effective control of ALS-resistant common chickweed in small grains.
- Fall-applied herbicides generally provided more consistent control of common chickweed than spring, but control can be achieved at both application times.
- Treatments containing fluroxypyr provided 92-98% chickweed control when applied in the fall and 84-99% control when applied in the spring
- In general, metribuzin alone or in combination provided at least 85% chickweed control, regardless of application timing.
- Thifensulfuron plus tribenuron premix (Harmony Extra) provided no more than 70% control when applied in the fall and as low as 37% when applied during the spring.
- Pyroxsulam (Powerflex), another Group 2 herbicide, provided 77% or less control. We would expect similar results from mesosulfuron (Osprey) or other ALS-inhibitors.
- Crop rotation and the use of other weed control tactics including different herbicide programs and modes of action provides the most reliable means of controlling ALS-resistant common chickweed.
Source : psu.edu