Pasture & Range: March 2003 Soils: March 2003

Have you ever needed to spray your pasture, but it was too windy? Or have you ever needed to spray but didn't want to damage your clovers and other legumes? Do you want to save money, cut down on herbicide rates and help the environment? Then consider a weed wiper as your herbicide application method. If you can graze desirable forages so that weeds are 6 inches taller than the forages, a weed wiper will work for you.

Speidel-brand weed wiper. A: Spigot to control flow. B: Height adjustment.

Many people are unfamiliar with wiper or wick applicators. However, they have been used for years to control volunteer corn in Midwestern soybean fields. The concept is simple. Herbicide solution, usually Roundup (glyphosate), is supplied to an absorbent surface. The herbicide soaked surface only contacts weeds taller than the crop. Chemical is transferred to the surface of the weeds as the applicator "wipes" over them. There are many variations, but the principle is the same.

Key elements include a surface that will hold solution without dripping, a way to prime the surface, a way to mount the unit so the height can be adjusted, and weeds that are taller than desirable plants.

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

In the most basic unit, the pipe is used as the reservoir for the herbicide. Flow is regulated with a throttling valve that controls the amount and rate of air that gets inside the pipe, thus regulating the amount and rate of solution that can leave the pipe. Other models connect the pipe to a tank with a pump. The pump is 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 about 8 inches long and overlap.

Rotowiper-brand weed wiper. A: Counter-rotating drum. B: Hooded spray boom to wet drum surface.

Many times it is necessary to wipe weeds from opposite directions to get thorough coverage. However, better models with hooded booms use a counter-rotating drum, which improves coverage and eliminates the need for this. Some units are mounted on the front of a 4-wheeler and 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 the height on the go.

There are many benefits to wiper applicators. First is the use of Roundup (glyphosate) herbicide. This allows control of almost any weed in any crop, as long as the weed is taller than the crop. An excellent example is johnsongrass control in bermudagrass hay. With the low cost of generic glyphosate, weed control can be done very economically (less than $1 per acre for medium weed density). Glyphosate is also more environmentally friendly than other herbicides.

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. Wipers can be used regardless of wind speed — a big advantage. They can also be used with herbicides containing 2,4-D, pichloram, dicamba and triclopyr. This can provide increased 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.