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What’s new in cereal-crop, forage-grass weed control

In February’s issue, Penn State University Extension weed specialists Bill Curran and Dwight Lingenfelter teamed up with Cornell University’s Russ Hahn for an update on corn and soybean weed control. They noted that common chickweed seemed to be developing resistance to Harmony SG, Harmony Extra and products containing thifensulfuron’s mode of control in small grains.

Key Points

Two products hold promise for chickweed control in wheat.

Paramount is the only labeled grass controller for grass forages.

Weed size, additives and spraying conditions affect control.

Following is a Curran-Lingenfelter-Hahn update on new products and labels for small grains and herbicides.

Products not expected to be labeled in 2011 for New York are noted with an asterisk (*).

Weed killers for small grains

Huskie 29.6L* (Bayer) contains pyrasulfotole (an HPPD-inhibitor) plus bromoxynil (Buctril). It controls common chickweed, wild buckwheat, mustards, prickly lettuce, lambsquarters, pigweed, smartweed, ragweed and velvetleaf in wheat, barley and triticale.

Apply it plus an ammonium sulfate solution or a urea-ammonium nitrate solution to small grains up to flag-leaf emergence, and to actively growing weeds with one to four leaves. You can also tank-mix it with other approved pesticides, using liquid nitrogen as a carrier in wheat.

Do not apply Huskie to crops undersown with legumes. Soybeans can be planted 4 months after application; alfalfa, corn, and potatoes after 9 months.

PowerFlex 7.5WDG* (Dow) is a new ALS-inhibitor herbicide containing pyroxsulam. It controls annual ryegrass, downy brome and cheat plus a few annual broadleaves such as non-ALS-resistant chickweed, mustards, henbit, wild buckwheat and hairy vetch.

Fall applications seem to provide the best control of grassy weeds. Apply once wheat reaches the three-leaf stage.

PowerFlex has a favorable crop rotation time frame. Soybeans can be planted after 3 months; other crops can be planted after 9 months.

New for grass forages

Paramount 75WG* (BASF) contains quinclorac as an active ingredient, and can be applied in cool-season grass pastures or hay. It’s currently the only herbicide labeled that controls some annual grasses in grass forages — foxtails, large crabgrass and barnyardgrass. It also has activity on broadleaves such as lambsquarters, ragweed, velvetleaf, annual morningglory, dandelion and field/hedge bindweed.

It can be applied in bromegrass, tall fescue, Kentucky bluegrass, orchardgrass and ryegrass. It’s also labeled for several warm-season grasses.

A seven-day waiting period is required before cutting. Paramount will severely injure or kill clovers, alfalfa and other legumes. Be cautious of crop rotation restrictions.

For more specific product details, rate recommendations and more about weed management, visit

Chickweed weapons are few

Chickweed herbicide resistance wasn’t totally unexpected. Some parts of Delaware, Maryland, Pennsylvania and Virginia have a long history of using Harmony products and other ALS herbicides in wheat.

The populations in Virginia and Maryland are resistant to at least a 32X application rate of Harmony Extra. They’re also cross-resistant to herbicides like Pursuit and Raptor.

Harmony Extra (thifensulfuron plus tribenuron) typically provides better control of common chickweed than Harmony (thifensulfuron).

If resistant populations are indeed evident, alternatives are quite limited. Herbicides such as 2,4-D and Banvel/Clarity generally provide only 60% to 70% chickweed control.

The same is true for other herbicides typically used in small grains. Starane Ultra (Dow) has been suggested as an option. This product is being used in the mid-Atlantic area to control ALS-resistant chickweed. It appears to have good crop safety.

Also, Huskie (Bayer) lists control of common chickweed, including ALS-biotypes. But data are limited.

Other control options such as Prowl H2O, Sencor, Valor, Axiom and Sharpen have been examined. But application timing and other restrictions are critical with these products.

Other reasons for poor weed control also need to be considered, such as adequate spray volume, inclusion of proper spray additives, weed size at application time, and temperature and other environmental conditions.

— Bill Curran and Dwight Lingenfelter

Corn products in the works

Two herbicides with pending labels were inadvertently left out of February’s article. Here are the details:

Zidua 85WG* (BASF) is a pyroxasulfone-contaning herbicide that’s expected to be labeled in early to mid-2011 for all types of corn, soybeans and wheat. The active ingredient will be premixed with other products.

Pyroxasulfone has annual grass activity similar to metolachlor (Dual) and acetochlor (Harness), and provides good control of several annual broadleaves. Use rates are up to eight times lower than Dual or Harness with comparable weed control.

Fierce 76WG* (Valent) contains pyroxasulfone plus flumioxazin (Valor SX), and will initially be labeled for burndown/residual use in field corn and soybeans. FMC will also have a pyroxasulfone premix.

Realm Q* (DuPont) will contain rimsulfuron (Resolve, ALS-inhibitor), mesotrione (Callisto, HPPD-inhibitor) and isoxadifen corn safener. The safener doesn’t totally eliminate potential crop injury, but lessens the impact.

Realm Q will likely be tank-mixed and applied post with glyphosate or, Ignite, or included in other postemergence herbicides to improve weed control spectrum.

This article published in the March, 2011 edition of AMERICAN AGRICULTURIST.

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