By Larry Steckel
Some folks may be tentatively planning to double crop soybean behind their corn crop this year. Several farmers did this last year and were able to plant soybeans in July after the corn was harvested. In several cases the double-crop soybeans made in the 30 bushel range. The question I get from these folks is what herbicides can they use in corn and come back with soybeans in July?
That quick a turnaround to soybeans eliminates our main corn "go to" herbicides like atrazine, Halex GT , Lexar, Capreno or even Impact. The plant back to soybean from atrazine is one year and for these other bleaching-based herbicides is 9 to 10 months. There are several good options that can provide weed control in corn where soybeans can be planted in July. Be sure if you go this route to plan to start off clean with tillage or a good burndown. Then, to acquire the most consistent control with the limitations on herbicide options, plan to utilize a herbicide program that utilizes a pre plant or pre emerge herbicide followed by something post emergence. A couple of suggestions are listed below.
Linuron is labeled in both soybeans and corn and can be used at rates of up to 0.75 lbs/A pre emergence in corn. Linuron would be a good substitute for atrazine where soybean will be planted in July. Linuron may be tankmixed with Dual Magnum and make a poor mans "Bicep" replacement in these cases. Another good option pre plant or pre emergence would be Verdict. Verdict is a premix of Sharpen and Outlook. The rate depends on the soil type but could be applied up to 15 oz/A and still be safe to plant soybeans in July.
From a post emergence perspective glyphosate or Liberty would be good possibilities in this situation. In straight RR corn where a herbicide may be needed to control emerged Palmer amaranth Status would be a good fit. In order to get good Palmer control apply the Status prior to the Palmer amaranth getting to 4 inches. For large Palmer amaranth in LL corn a tankmix of Status and Liberty will provide pretty good control of even 8- 10-inch Palmer. The plant back to soybean from a Status application is 30 days.