As we tackle the issues of weed resistance management, weeds like marestail have been very problematic this season. One of the factors that made marestail harder to control in burndown applications this spring was that winter 2022-23 was mild, allowing the marestail to develop to a more advanced growth stage by the time of application. As we approach next season, we should consider things that can improve our control of this troublesome weed.

Marestail (or horseweed) typically has two primary periods of emergence—one in the late summer/fall and the other in the spring. Managing both flushes can be challenging; however, there can be good opportunities for effective marestail management with various tactics in the fall.

• Cover Crops

Cover crops can be very beneficial in managing winter annuals and overall minimizing weed pressure. However, specific cover crops are vital to target marestail control. Cover crop blends that include clovers, radishes, peas, etc., will make it impossible to use any herbicide control late in the fall or early spring. Consider a cereal cover crop like rye or wheat on acres where you need to aggressively target marestail because, in cereal crops, you have herbicide options in both the fall and spring. Products like 2,4-D and dicamba can be sprayed in the small grain cover crop this fall (or early spring) to check smaller marestail seedlings.

• Winter Wheat and Barley Fields

In production fields of winter wheat or barley, it is often necessary to manage marestail. Fall applications of products like 2,4-D, dicamba, MCPA, Huskie, or Quelex are helpful when controlling marestail and other types of broadleaf weeds.

• Fall Burndown Herbicide Applications

In fields that will be fallow (i.e., no cover crop) this winter, fall, and even late fall, herbicide applications, including some residual activity, can be beneficial in controlling marestail. Killing the marestail that germinates in the fall, especially when the seedlings and rosettes are tiny and more easily controlled with herbicides, dramatically improves your control for the following season. Once the marestail gets beyond the rosette stage and starts to bolt and grow vertically, it becomes much harder to control. In most cases, a basic tank mixture of 2,4-D ester (1 pint/A) plus glyphosate (1 quart) plus metribuzin (3-5 oz DF) tends to provide adequate control of marestail and other weed species. It is relatively economical when sprayed in the fall. Other products such as dicamba (8 fl. oz.), Gramoxone, Liberty, Valor, Canopy/Cloak (if planting soybeans next season), or simazine (corn) are helpful as well, but watch out for restrictions. Also, try to keep the fall burndown herbicide costs at a minimum since you will need to account for other herbicide costs next spring to control marestail in the crop.

• Tillage 

While tillage is not an option for every grower or every acre, it’s an excellent management tool for marestail. Marestail is a surface germinating weed, so tillage that buries the seed stops it from germinating. Tillage doesn’t need to be deep tillage; even aggressive vertical tillage reduces marestail significantly.

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Start planning in the fall for next season, and you will successfully manage this tough-to-control weed. If you have more questions about weed control, call us; we will gladly help!

Co-authors:

Dervin Druist, PowerAG Agronomist

Dwight Lingenfelter, PSU Weed Science