Larry Steckel, Extension Weed Specialist
Good News: With a few exceptions, horseweed (marestail) control with burndown applications this spring has been much better than the last couple of years. The main reason for this is the horseweed has been much smaller than last year when herbicide applications were made.
According to NOAA statistics this has been the 2nd coldest spring in recorded history. Only the spring of 1975 was colder. The cold conditions this winter and spring have kept the growth of horseweed in check. Small horseweed is simply much easier to control.
Bad News: Cover crops have been very difficult to control. I have had a number of calls from folks who are frustrated by poor control of wheat, rye, vetch and crimson clover this spring. We have had similar results in research as well. Again the cold temperatures had an effect. This time it was negative as the cold conditions made control of cover crops less consistent. Most have had to resort to some kind of two pass program to control their cover crops. A number of folks have added clethodim into the burndown to take out rye and wheat.
It is no news to anyone that this has been a very wet spring. In Jackson we have had 25" of rain as of April 30. The long term average here is 17" at this point in the year. Last year was the opposite flip of the coin with only 12" of rain by April 30. The very wet spring has slowed down herbicide applications to the point that many have yet to go out. Horseweed is getting large and Palmer is emerging. The horseweed is beginning to bolt. I was hoping that the very small Palmer would have frozen out with the frost we had last week but no such luck! On the positive side it has not grown though and is still just ¼ to ½" tall.
There have been a number of calls this week from folks who are planning last minute burndown strategies in these fields that have yet to be touched. Typically they want to apply the herbicide and start planting hopefully by next week.
In soybeans the best burndown option on the very small Palmer amaranth and large horseweed this spring has been Verdict. In a couple tests we just rated that were sprayed last week Verdict plus MSO plus glyphosate had provided 99% control of small Palmer and 6" tall horseweed. Soybeans may be planted anytime after a Verdict application. We only got about 80% control of horseweed with a pint of 2,4-D with glyphosate. The Palmer looked to be going down as well with the 2,4-D treatment. Soybeans may be planted 7 days after a pint of 2,4-D. Dicamba is another option but the plant back is 14 days to soybeans with 8 ozs/A and 30 days for anything over 8 ozs.
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