Del Voight – Penn State Extension
Coming into work this morning I saw a grower heading out to apply spring burn down on one of their fields. I no sooner got into the office and I received a call on spray or not to spray. The dialogue is whether to go ahead and spray today temp 45 night time 30. The growers want to apply glyphosate and 2,4-D and not switch to glufosinate or paraquat. SO focusing on the glyphosate and 2,4-D. Bottom line the rye and other weeds have to be actively growing for the products to work. They can be applied and decent control might result but one might find themselves treating again for missed spots in the field. Here are some rules of thumb, if night time temperatures are 50 or above 2 days before and 2 days after application the application should work just fine but expect a slow process. However if night time temps are 32 or below 2 days before or 2 days after application then poor results will likely result( WITH THESE PRODUCTS). In this case doubling the rate would be beneficial to ensure the concentration of salt int the plant stays high so it gets absorbed when growth returns.
In Illinois, back in 2003 research was funded by the Illinois Soybean Program Operating Board to look at systemic (glyphosate and paraquat)–Christy Sprague and Aaron Hager . There were three herbicide treatments, glyphosate (Roundup UltraMax), paraquat (Gramoxone Max), and paraquat (Gramoxone Max) plus metribuzin (Sencor), were applied at six different application timings based on daytime high air temperatures ranging from 47° to 87°F. The herbicides included one herbicide that was systemic in nature (glyphosate), one that was contact in nature (paraquat), and a contact herbicide combined with a herbicide that had soil residual activity (paraquat + metribuzin). Weeds evaluated included common chickweed and henbit. Overall what they found was that increases in temperature significantly enhanced weed control and reduced weed biomass. The treatment least affected by temperature was paraquat plus metribuzin. This may be attributed to the soil residual activity of metribuzin. Some weed control provided by this treatment at lower temperatures may have come from this residual activity. Differences also appear to exist in how application temperature affects control of these two species. Temperature had little affect on common chickweed control with glyphosate; however, application temperature significantly affected glyphosate activity on henbit. When deciding whether it is too cold to spray, make sure to consider what weeds are out there and what type of herbicide you will be using. Armed with some information I would advise not to be spraying today wait until warmer temperatures come back or consider another herbicide choice.
