Don’t Forget To Include 2,4-D in Burndown Applications
A little over a week ago about the only weed I noted in corn stalks was dandelion. Now, I see that summer annual weeds such as giant ragweed, lambsquarters, and a few others have started to emerge in central and north-central Ohio. The emergence of these weeds increases the need for appropriate preplant (burndown) herbicide mixtures in no-till crops.
This past winter you may have been considering whether or not you need to add 2,4-D with your burndown applications. Because of the prevalence of dandelion and glyphosate-resistant weeds the addition of 2,4-D in preplant herbicide burndown applications is very important in achieving effective weed control prior to planting. Unfortunately, there are several weeds that have expressed glyphosate resistance (or tolerance, whatever you want to call it). Just a few examples of glyphosate tolerant weeds in our area include marestail, common/ giant ragweed, and lambsquarters. Of these, I am most concerned with marestail (Conyza canadensis). This weed is difficult to control in the best of situations, let alone when it gets > 8″. OSU Weed Scientist Mark Loux recommends controlling this weed when it is 4″-6″ or smaller. I completely agree, as I have observed the difficulting in controlling this weed once it bolts. And, unfortunately, postemergence control options with this weed are usually not overly successful.
We are still early enough in the season that it is more important to include 2,4-D in preplant herbicide applications rather than planting the crops and controlling weeds long after planting. For the latest updates on weed control strategies, visit the OSU C.O.R.N. newsletter at http://corn.osu.edu/.
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Edit (04/08/09): I was asked ‘What is a burndown?’ Good question, and I apologize for using the ag jargon. A burndown is a herbicide application made to an ag field several days (or even a couple of weeks) prior to planting. Burndown applications are made in no till fields.