by Sally Colby
Hay is an important crop for livestock producers, and should be treated the same as any other crop when it comes to weed control. Weedy hay results in decreased yields, short-lived stands and potential harmful effects to livestock.
Weeds in forages compete for nutrients, light moisture and space. They reduce the quality of forage, and intake may be influenced. In a pasture setting, cattle often eat both desirable and undesirable species, and can possibly ingest harmful or injurious portions of plants. Some weeds are toxic when dried with hay, and although cattle can usually sort out weeds in straight dry hay, weeds contained in large bales that are chopped and mixed with a ration are nearly impossible to sort.
Penn State weed scientist Dwight Lingenfelter says forage weed management is critical to a good hay crop, and listed several reasons that weeds in hay fields aren’t adequately controlled.
“One problem is that weeds are often misidentified,” said Lingenfelter. “They have to be identified properly, especially in a forage setting. The species and life cycle of the weed impact how we manage it.”
When weeds aren’t properly identified, producers tend to use the wrong product to treat fields or apply the product at the wrong time. For example herbicides should not be applied when plants are stressed from drought or heat. Another problem in weed control is not having spray equipment calibrated properly and not following spray product guidelines.
Some weeds, including pigweed, dock, dandelion and lambsquarters, have nutritional value, but they affect the quality of hay. “They dry down differently,” said Lingenfelter. “They reduce the quality of the forage — we don’t want them in the mix.”
Weeds can greatly impact the overall carrying capacity of a hayfield. “Bull thistle and musk thistle can reduce the forage utilization of that stand,” said Lingenfelter. “For a beef operation, the reduction can be between 42 and 72 percent. Animals don’t like to put their nose into that sward.”
One of the challenges in weed control is that life cycles and growth patterns vary. This causes problems both during establishment and throughout the life of the stand. Understanding the growth habits of summer annuals, winter annuals and biennials is important to weed control.
Winter annuals include purple deadnettle, henbit and yellow rocket. Chickweed is a common problem in alfalfa, while marestail is resistant to glyphosate and some of the ALS herbicides.
Summer annuals include eastern black nightshade (which can also act as a short-lived perennial), cocklebur, the pigweeds, common ragweed, jimsonweed and some grasses such as crabgrass.
Biennials, which have a two-year life cycle include bull thistle, burdock, poison hemlock. Simple perennials have a taproot and a crown, similar to the structure of alfalfa. “Broadleaf plantain, buckhorn plantain, dandelion, dock (curly, broadleaf).
Creeping or woody perennials include common milkweed, which Lingenfelter says can be very challenging to manage, especially in pastures and hayfields that have had a history of poor management or overgrazing. Weeds in this category include quackgrass, Canada thistle, horse nettle, buttercup and multiflora rose.
For weed identification and an understanding of growth habits, Lingenfelter recommends a book titled ‘Weeds of the Northeast’, which includes weed species found from Virginia to New England and west to Wisconsin. Another resource, especially for unusual weeds and wildflowers, is ‘Newcomb’s Wildflower Guide’. Lingenfelter also advises farmers to take advantage of university websites that provide information about weed identification and control.
When it comes to poisonous plants, Lingenfelter cautions farmers to be aware that the information in some books and other sources can be incorrect. “Sometimes they take an alarmist attitude,” said Lingenfelter. “The university or science-based resources are best.” Lingenfelter says the University of Pennsylvania maintains an excellent reference for poisonous plants, which is available on line at http://cal.vet.upenn.edu/projects/poison/index.html .
A combination of measures ensures the best weed control in a forage stand. For establishing hay or pasture, producers should select the species that are appropriate for the region, take soil tests prior to planting and throughout the life of the stand, fertilize according to soil tests, manage harvest and watch for signs of overgrazing. It’s also important to keep fencerows clean — messy fencerows can mean more weeds in pastures. Weeds can be controlled mechanically, with routine mowing at the appropriate time. “We suggest around flowering time, or seed head formation,” said Lingenfelter. “If necessary, treat weeds by hand.”
Weed control during the year of establishment is critical, and it’s the time to get rid of hard-to-control weeds such as perennials. “Make sure you get the bush and brush species under control,” said Lingenfelter. “The herbaceous perennials should be removed the fall before planting.” Lingenfelter advises growers to purchase certified seed and be aware of the potential for manure to contain weed seeds. Fertility and a well-prepared, firm seedbed are important in establishing hay. Consider companion crops such as triticale or oats to help the stand get started. “It’s the first 60 days that are the most important to give the crop a competitive advantage,” said Lingenfelter.
Another important aspect of weed management includes the use of appropriate herbicides. Most forage herbicides are applied to existing foliage during the post-emergent stage. However, herbicide options for hay and pasture are limited, especially for controlling broadleaf weeds in a legume/grass mix.
“The number one reason people don’t control weeds in pastures is that they don’t want to kill the clover,” said Lingenfelter, adding that some white clovers tolerate 2,4-D. “Is the clover something that you planted, or a short, wild type that isn’t providing much forage clover? Decide which is more important — getting rid of weeds or saving the clover.”
When is it time to rotate out of a pasture or hayfield? “If weeds or bare areas comprise less than 30 percent of the field, good agronomic practices will improve the field,” said Lingenfelter. “Use of the appropriate herbicide and mowing can provide improvement. If weeds and bare ground are between 30 percent and 50 percent, a combination of herbicide and overseeding for an improved stand should be considered. If weeds and bare ground are more than 50 percent, evaluate how that happened. Renovation might improve the stand in the long run, but it’s important to understand what led to the need for renovation. If the stand is too weedy, overgrazed or has poor fertility, simply renovating will not have a long-lasting effect on the stand. It’s important to understand how the stand got that way — renovate only as a last resort.”
Managing weeds in hay fields
by Sally Colby