Opinion

Marestail control

Tuesday, July 1, 2014

Marestail, sometimes called horse weed, is one weed that has given farmers a lot of headaches in the last few years.

This annual weed can follow either a winter or summer lifecycle, making it incredibly difficult to control. In the fall, Marestail can form a basal rosette to survive the winter. In the spring the rosette bolts can grow up to six-feet tall.

Marestail seed is ready to germinate when I falls off the plant and can germinate and can contribute to a summer life cycle. The Marestail that has germinated in the fall and enters in the basal form have up to 84 percent survival rate to bolt the next spring.

Marestail begins to bolt in mid Aprils and will flower at the end of July. Marestail is self-compatible and self-pollinate however is can also cross with other Marestail populations which can spread the Glyphosate resistant in the plant population. Marestail can produced up to 200,000 seeds per plant and be 80 percent viability.

Maretail also tolerates drought conditions well. Marestail also can harbor diseases and insects. It is known to be a host for the tarnish plant bug, a pest in alfalfa, it is also a host for aster yellows, a viral disease that can be transmitted by leaf hoppers.

Marestail have increased in populations for several factors. Surprisingly crop rotation is not a factor to do with its prevalence. It can be just a prevalent in corn-soybean rotations as it is in double-crop soybeans. Decrease tillage was found to be a factor in Marestail prevalence.

A study found about eight Marestail of conveniently tilled fields as compared to 61 percent of no-till in a study done at Purdue. Herbicide resistance is another reason that Marestail has become more prevalent it is able to build resistance to many herbicide modes of actions.

In 2000 it was documented that Marestail had developed a resistance to glyphosate Marestail also been found to be resistant to Paraquat. Marestail had also become resist to atrazine. It was only a matter of time until we find a population of Marestail that was resistant to ALS inhibitor herbicides.

Control of marestail is very difficult. For control of Marestail no-till soybeans, there must have effect control of prior to planting soybeans. Soybeans planted early to mid-May will also require a residual herbicide to control later emerging plants. This should reduce post-emergence treatments.

A couple of principles to follow when formulating your control program: Always include a 2,4 D ester in herbicide treatments when it possible, Herbicides should be applied when the plant are 4-6 inches tall, Applied herbicide in the fall will help control emerged Marestail but may not adequately control spring emergent plants and will require spring applications of herbicides.

Prior to May, there should have a residual herbicide. Controlling Marestail in the seedling or rosette state in April can be extremely effective because small plant are easier to control. When Marestail gets taller than six inches it is very difficult to control and will take some intensive management to get it back under control.

Liberty link soybeans may be the most effective control of Marestail. Only time will tell if liberty link soybean technology will help over time. Marestail is not a new problem but is become more of a problem in most no-till fields. It will take a lot of vigilance and consistence to control Marestail. Scouting your fields is the most effective way to time this treatment for effective control.

If you would like more information, contact the Purdue extension office at 653-8411 or email Ann Delchambre at adelchambre@purdue.edu .