Over the past several months, the price of glyphosate has increased dramatically. Brand name glyphosate now costs about twice as much per gallon as it did at this same time a year ago. Many have speculated that the increased price is due to reduced glyphosate supplies and increased demand. The high commodity prices are likely playing a role in these new prices as well. Regardless, for those who have not purchased their glyphosate for the year, or for those who will have to re-fill their bulk containers in mid-season, there may be some "sticker shock" when you get the glyphosate bill this year.
With this increase in price, there are several things that come to mind. First and foremost, this price increase now makes most preemergence soybean herbicides economically feasible. In the past, the cost of two applications of glyphosate in Roundup Ready soybeans has been "unbeatable" from an economic standpoint. Now, at a chemical cost of about $11 or $12 per acre for a brand name glyphosate treatment, most preemergence soybean herbicides like Authority First, Boundary, Canopy, Dual II Magnum, Envive, IntRRo, Prefix, Prowl H2O, Sonic, Valor and Valor XLT will cost about the same or less than a glyphosate treatment. Although generic glyphosate products will likely remain slightly lower in cost than many of these preemergence treatments, I still think there is a strong case to be made for the use of preemergence herbicides in soybean.
One reason to consider preemergence herbicides is to achieve maximum crop yield. Results from a survey we conducted last year in Missouri revealed that the majority of first-pass glyphosate applications in soybeans are made when weeds are 7 to 10 inches tall. At this point, yield loss will probably have already occurred in most fields. A preemergence herbicide will eliminate much of the weed competition and yield loss that can occur in these situations and still allow growers to make a timely glyphosate application for any weed escapes or species that emerge later in the season. Another reason to consider a preemergence herbicide in soybeans is to rotate herbicides and prevent or manage glyphosate-resistant weed species. Results from the survey we conducted last year also indicated that glyphosate-resistant waterhemp now occurs on at least four percent of the soybean acres in Missouri. Many of the preemergence herbicides mentioned previously will provide good control of this species in soybeans. Continuing with a glyphosate-only program in an area where you know you have glyphosate-resistant weeds will allow these weeds to proliferate and be that much more of a problem next year.
Another thing that some may be tempted to do in response to the increased price of glyphosate is to reduce the glyphosate rate. This is a practice that we should avoid at all costs, and one that I certainly would not recommend. Reduced rates usually translate into reduced weed control and increased yield loss, and with current commodity prices the last thing we need to do is to cut rates in order to try to save a few cents. It is likely that what will actually occur is that the money you were trying to save on glyphosate will be lost in the form of soybean yield at the end of the season.
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REVISED: April 5, 2012