Need to spray pastures, but it's too windy, or you're worried about damage to clovers or other legumes? Weed wiping may be your most cost-effective answer, says Jim Johnson, Noble Foundation, Ardmore, OK.

“If you can graze desirable forages so that weeds are 6 in. taller than the forages, a weed wiper will work for you,” he says.

Wiper or wick applicators are common in the Midwest to control volunteer corn in soybean fields. It involves supplying herbicide solution to an absorbent surface that, when passed over the field, wipes herbicide on any weeds taller than the crop.

What's needed, says Johnson, is a surface that holds solution without dripping, a way to prime the surface, a way to mount the unit so height can be adjusted, and weeds taller than the desirable plants.

In one version, a pipe with small holes in the bottom is covered with an absorbent canvas. The pipe, filled with herbicide solution, is mounted horizontally on a vehicle so it rides above the crop but will contact the weeds. In use, the covering wicks the herbicide out of the pipe through the small holes and applies chemical to weeds as the unit passes over them.

In the most basic unit, the pipe is used as the reservoir for the herbicide. A throttling valve is used to regulate the amount and rate of air inside the pipe.

Other models connect the pipe to a tank with a pump that's turned on and off as needed to prime the wiper. Better models mount a hooded spray boom above the wiping surface to wet it as needed. Rather than canvas, some wick applicators use braided cotton rope plumbed into a pipe. Rope sections are 8 in. long and overlap.

“Many times it's necessary to wipe weeds from opposite directions to get thorough coverage,” Johnson says. “But, better models with hooded booms use a counter-rotating drum, which improves coverage and eliminates the need.”

Some units are mounted on the front of a four-wheeler. Others are pulled behind like a cart with wheels on the ends. Mounting the unit to the front of a loader makes it easy to adjust height on the go, Johnson adds.

He says one benefit to wiper applicators is that the use of Roundup (glyphosate) allows control of almost any weed in any crop as long as weeds are taller than the crop. An excellent example is johnsongrass control in bermudagrass hay. Using generic glyphosate, weed control can be done for less than $1/acre for medium weed density.

“With a properly adjusted wiper, herbicide is only applied to the weeds. This reduces the amount of herbicide used per acre and introduced into the environment and reduces or eliminates damage to non-target species,” Johnson says.

Plus, wipers eliminate wind as a factor. And, herbicides with 2,4-D, pichloram, dicamba or triclopyr can also be used to increase control of tougher perennials like horse nettle, briars and tree sprouts.

“You can purchase wipers or wicks fully assembled, as kits you put together or build one completely from scratch. They can be small hand-held units or as large as 45 feet,” Johnson says.
— Noble Foundation, Ardmore, OK; www.noble.org/news; 580/224-6379l