Burndown Considerations With Cold Temperatures

JACKSON, TENN.

   The growing season last year seemed to run about 3 weeks ahead of “normal”. This season seems to be running, if anything, about 2 weeks later than normal. It looks like this upcoming week will at least be a little warmer than last week with lows in the high 30s (which beats below freezing) and highs in the high 50s to low 60s. There have been a lot of questions about applying burndowns during cold weather. The main question is should we be applying burndown applications now or wait for warmer weather.

   In general most herbicides do not work well with the temperatures we saw this last week 3/24 to 3/31 and will perform only a little better with the weather forcasted for this upcoming weeek 4/1 to 4/7. Translocating type herbicides like glyphosate that have no soil activity will likely work very slowly and provide inconsistent control. Other herbicides like dicamba or 2,4-D should provide better activity as they will provide some soil activity later as the winter annual weeds begin to grow. The light activated herbicides like atrazine, Gramoxone and Sharpen should still work though again the consistency will not be as good as if temperatures were 20 degrees warmer. In other words with everything being equal it would be best to wait for warmer temperatures.

   Unfortunately, time is not a luxury this spring. Planting will commence as soon as it warms up. Therefore many burndown applications will begin shortly regardless of temperature. The cold temperatures can at least be partially overcome by utilizing higher rates of the herbicides mentioned. For example I would not use anything less than a pound of glyphosate (32 oz/A of Roundup Powermax) with the temperatures forecasted for this week. Moreover in corn a quart of atrazine or simazine tankmixed in with any of the standard burndown mixtures should greatly improve the consistency of the winter annual weed control. Δ

DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee