With spring in sight, this is a good time to ask: Have you completed your planning and preparation for the spring planting season? Specifically for those who intend to plant soybeans, what is your plan to control marestail?
Yield reduction can be severe if it is not controlled and the window to control this weed is narrow. This has been a topic in our private pesticide recertification meetings this winter. Here are some key concepts to keep in mind.
Control of marestail begins with an understanding of the life-cycle and biology of this weed. It has two primary periods of emergence; the first is late summer into fall and the second is late March through June. Marestail begins growth as a rosette followed by stem elongation (bolting) and growth to a mature height from 3 to 6 feet. Seed production is prodigious. Each plant can produce up to two-hundred thousand seeds. To make matters worse, this is a small light seed that is easily distributed by the wind. If you have not already encountered this weed in your field, you will. The goal should be to control marestail when it is 4 inches or less in height. One more piece of bad news: many marestail populations have developed resistance to several classes of chemical herbicides, glyphosate among them.
The current recommendation from Extension weed specialists is that a field must start free of marestail at the time of soybean planting. In order to do this there are several options. The most common option for minimum and no-till fields is an herbicide program that includes burndown herbicides plus a residual herbicide.
Remember, once a marestail plant begins to bolt and elongate, you have lost the battle. It is impossible to control marestail at that growth stage with any current herbicide. You will have to decide how practical or possible hand pulling and/or cultivation is in that case. For most growers it will be all about how much yield will be lost. Last fall did not allow growers to implement a fall marestail control program, so this spring is going to be a critical time period. Do you have a plan, are you prepared?