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January 26, 2010

Pasture herbicide use and control

by Doug Toburen

After all the snow, ice and cold temperatures, pasture weed control is probably the last thing on the minds of producers.

According to University of Missouri Extension Agronomist Brie Menjoulet, however, now is the time to plan a pasture weed management strategy.

She recently explained the ins and outs of pasture herbicides at the Webster County Soils and Crops Conference held in Marshfield, Mo.

“The first thing you need to know about pasture herbicides is how they work,” Menjoulet explained. “Herbicides must disrupt one or more vital plant processes in order to kill the plant.”

And in order to disrupt plant processes the herbicide is usually applied in a foliar method when the plant is actively growing.

Menjoulet did mention that there are some herbicides that can be applied into the soil but they are more often used for row crops and alfalfa.

When it comes to pasture weed control in southwest Missouri she said the most common herbicides included:

•2,4-D

•Picloram—(Tordon)

•Triclopyr—(Remedy & Garlon 4)

•Dicamba—(Banvel & Clarity)

•Aminopyralid—(Milestone)

•Metsulfuron—(Cimarron & Escort)

These products, according to Menjoulet, are effective in weed control by themselves. However, she said combining chemicals will increase the spectrum of weeds controlled.

“The important thing to remember is to read all labels and active ingredients before combining chemicals,” she explained.

When using any herbicide, reading the label is the most important thing. The second most important thing is application timing.

“Application timing is crucial,” Menjoulet said. “You have to spray these weeds when they are actively growing in order to get a good kill.”

Her recommendations for application timing are as follows:

•Summer annuals—

Control when they are young and actively growing, usually in spring.

Summer annual weeds include: Common Cocklebur, Bitter sneezeweed, Smartweed, Perilla Mint, Redroot Pigweed, Jimsonweed, Lambsquarter and Ragweed.

•Winter annuals—

Control when young and actively growing usually in fall or early spring.

Winter annual weeds include: henbit, horseweed, deadnettle, chickweed, Virginia Pepperweed and Shepherdspurse.

For biennials, the best time to control is when the plant is in the rosette stage which is in fall or early spring.

Perennials can be controlled during the pre-bloom to bloom stage.

When it comes to effective pasture weed control, according to Menjoulet, there are a few questions to ask.

“Before you can control weeds in your pastures you have to know what the weed is, therefore, identifying the weed is the first step,” she explained.

In addition to that, knowing what stage of growth the weed is in is key.

“If the weed has already gone through the growth cycle and has a seed head it is better to save your money and work on controlling it the next year,” Menjoulet explained.

In addition to identifying weeds and controlling them in their growth cycles, she recommended checking the weather forecast.

“If rain is in the forecast then it is not a good time to consider spraying,” she said.

Finally, she told producers, the better their forage growth the less problems they will have with weed encroachment.

“When you are dealing with pastures, keep your grass growing vigorously to keep weed invasion down. The weeds just can’t compete with good grass growth,” she concluded.

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