Marestail – Weed ID Wednesday

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Marestail, also known as horseweed, is a common occurrence across pastures, haylands, and row crop fields. It can be anywhere from 1 foot to 6 feet tall when mature, and one taller plant can produce more than 200,000 seeds alone. It is a tall, more slender plant with narrow leaves that go from a darker to a lighter green as it gets closer to the stem. Marestail is a winter and summer annual and reproduces by seed. It starts out growing as a rosette and then “bolts” and starts growing upward. The growing pattern and seed rate are important to know when considering control options.

It is important to scout your pastures and know what weeds you have growing so that you can select an appropriate control method. Marestail is a weed that you would want to control sooner rather than later, because infestations can happen quickly since it produces a high number of seeds and is adaptable to a variety of growing conditions.

If you catch the presence of marestail before it spreads, hand pulling is an effective form of control. If it is more than you can pull by hand, mowing is a good way to reduce seed production and spread. It is important to catch marestail before it goes to seed for mowing to be of any help. It would be best for the weed to be “bolted” already, as the mower may not reach it well enough if it is still in rosette.

Chemical control options of marestail are slightly more complicated and not exactly cost effective, unless you make your choices wisely. Since marestail spreads by seed, spraying the plant only provides control for that specific growing season. Research shows that seeds are viable for germination for 2-3 years, but some has been found viable for up to 20 years. If you choose to apply an herbicide for marestail, consider one with residual properties that would help reduce seed viability that are already on the ground in your pastures.

Of course, one of the best weed control methods for most pasture situations is to grow such great grass that the weeds do not have room to stick around. The easiest way to find out what your pasture needs is to take a quick soil sample. If you need assistance with learning how to take a soil sample, call your local Extension office!

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