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Herbicide Activity in Cold Weather (05/04/17)

This may not apply now that temperatures have warmed but the answer should be a good refresher.

Herbicide Activity in Cold Weather

This may not apply now that temperatures have warmed but the answer should be a good refresher.

Question: I’ve had a couple calls this morning asking about spraying burndown herbicides in cold temps, specifically Sharpen. What are you advising for your products?

Answer: Herbicide application should be postponed until consistent warm temperatures. Contact herbicides used for burndown, such as Sharpen, Verdict, and systemic herbicides, such as glyphosate, and phenoxys (2,4-D) are much less active at low temperatures. Sunlight can be as important as temperature for contact herbicides. Daytime temperatures of 50 degrees or above is ideal and nighttime lows above freezing. Adjuvants can increase the activity of these herbicides in adverse conditions such as these. Use 1 to 1.5 pt/A of MSO or 1 pt/A of an HSMOC (MSO based) and 8.5 lbs/100 equivalent of AMS or at least 1.25 gal/100 gal of UAN.

Cold temperatures may also plug nozzles with some mixtures.

Rich Zollinger

Extension Weed Specialist

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