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Extension agent: Healthy pastures require diligent weed control

By DOROTHY NOBLE
AFP Correspondent

GRANTVILLE, Pa. (March 28, 2017) — Dwight Lingenfelter, Penn State Extension associate, presented data on how weeds impact pastures and measures to cope with weed pressure at the recent Pennsylvania Forage Conference.
For every pound of weeds present, Lingenfelter said, available desirable forage is reduced by a pound. What’s more, weeds reduce forage quality, carrying/stocking capacity and forage intake.
Dairy/beef and horses/recreation preferences differ, and animals do not graze close to thistle and spiny plants. Unpalatable plant species tend to build over time.
Effective control begins with establishing healthy pastures, Lingenfelter said.
Weeds obviously compete for light, nutrients, moisture, and growing space. Lower quality affects feed value. Also, some weeds have proven injurious to livestock, particularly to their mouths, hides and hooves. Weeds also often serve as insect and pathogen hosts.
However, some weeds—lambsquarters, pigweed, dandelion and dock—can be high quality forages depending on their growth stage.
Lingenfelter explained several reasons for poor weed control. He listed historically weedy fields and poor ‘agronomics’ with overall stand management. Plus, he named numerous factors including incorrect weed identification, wrong product usage, faulty sprayer calibration, bad timing for the particular species, excessive wind speed for accuracy and not following label guidelines.
Integrated weed management employs a variety of cultural, mechanical and chemical control methods. Cultural controls involve using competitive species mixtures such as legumes-grasses, maintaining optimum soil fertility and pH, properly timing hay harvest plus avoiding too-frequent harvesting, managing grazing to avoid either continuous or rotational overgrazing, keeping fence rows clean and managing insects and disease pests.
Mechanical techniques of IWM include routinely and properly mowing pastures, and hand removing weeds when necessary.
The IWM chemical method includes usage of herbicides when appropriate.
Lingenfelter measured the affects of weeds with two examples:
The average annual total growth of cool season perennial pasture is 6,000 pounds dry matter per acre. Using a typical measure of 20 percent weeds, it means that 1,200 pounds of weeds is produced. That results in reduced animal gains and a decrease in pasture carrying capacity. The remaining 4,800 pounds forage dry matter per acre, with 2.5 percent body weight consumed, equals 0.5 animal unit per acre stocking rate. Lingenfelter pointed out that 20 percent weeds indicates that a 100 acre farm will carry 39 mature cows.
In the second example, Lingenfelter calculated that if the pasture composition is reduced to 5 per cent weeds, only 300 pounds of weeds will be produced per acre. In this example, the remaining 5,700 pounds forage dry matter per acre, at 2.5 percent body weight consumed would equal 0.65 animal unit per acre stocking rate. Consequently, the 100 acre farm will now carry 50 mature cows.
Grazing practices, too, affect weed management. When pastures are overgrazed and forages are eliminated, weeds fill in bare spots and thrive.
Lingenfelter pointed to a study by forage extension specialist Jessica Williamson at Penn State. The preliminary results showed that overall, the continuous grazing system resulted in more weeds than a rotational system. The weeds involved included milkweed, plantain, Canada and bull thistle and wild carrot. Orchard grass and tall fescue measured higher in rotational systems, while Kentucky bluegrass, red and white clover produced greater amounts in a continuous grazing system.