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Spotty Rains mean Preemergence Herbicides did not get Activated and there are Weed Escapes (05/24/18)

Many growers used preemergence herbicides but have not received sufficient precipitation to activate herbicides. Don’t worry about the PREs, they will get activated when it rains. The question is what to do about the emerged weeds. Control them as soon as possible since small weeds are easier to control than large weeds.

Spotty Rains mean Preemergence Herbicides did not get Activated and there are Weed Escapes

Many growers used preemergence herbicides but have not received sufficient precipitation to activate herbicides. Don’t worry about the PREs, they will get activated when it rains. The question is what to do about the emerged weeds. Control them as soon as possible since small weeds are easier to control than large weeds.

Emphasis should especially be on herbicide resistant weeds like kochia, common ragweed and waterhemp. Small weeds or weeds less than 3-inches are more susceptible to herbicide than large weeds. Even weeds with low level herbicide resistance are more susceptible at 1-inch than at larger growth stages.

Use full herbicide rates and adjuvants, when appropriate. Full rates will kill weeds with low level resistance. Reduced rates allow plants with low-level resistance to survive, hybridize and produce progeny with elevated resistance.

A caution for dry soils or fields that have not achieved full stands: select herbicides rate that are a compromise between weed efficacy and crop safety. For sugarbeet growers, apply Betamix at between 10 and 12 fluid ounces per acre for sugarbeet up to 2-leaves. Add ethofumesate at four fluid ounces per acre. A second option is UpBeet at 0.5 to 0.75 ounces per acre. However, a grower needs to be aware of areas where there are ALS (SOA 2) resistant weed biotypes.

Tom Peters

Extension Sugarbeet Agronomist

NDSU & U of MN

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