Ragweed is easy to identify because it produces noxious pollen that causes hay fever symptoms like itchy eyes and a runny nose. If you are noticing these symptoms while grazing or haying your pasture you probably have a serious problem with ragweed.
The good news is that with timely shredding, mowing, and fertilization practices ragweed can be eliminated from your pastures.
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For the past couple of years ragweed growth has exploded in many pastures. This is due to timely spring rains encouraging germination and seedling growth. It is also aided by sunny dry falls that help seed development. This weed is not good for livestock forage and is high in allergens. The seedheads produce abundant pollen and can trigger hay fever symptoms like itchy, watery eyes, a runny nose and cough.
It can be controlled with a variety of methods. Shredding ragweed before flowering will reduce the amount of pollen produced. It will also prevent the plants from producing seeds that will contaminate other forages. In addition, grazing management practices that maintain competition with grass and a dense leaf canopy from late May through June will decrease the growth of ragweed. In areas that have been grazed or hayed heavily, a quart of 2,4-D or Grazon after grazing can help control small plants and seedlings.
Regular mowing is another preventative measure against ragweed. This will keep it from spreading by reducing its height and it is especially important to mow when the plants are in bloom. Herbicides can also provide season long control of both Common and Giant ragweed. A post-emergent spray of 2,4-D Amine Selective Weed Killer applied when the plants are 3-5 inches tall will significantly reduce their growth. Remember to always use proper personal protective equipment when handling herbicides. This includes wearing a mask, jeans and long-sleeved shirt, gloves and goggles. Also, be sure to read and follow all the label directions.
Ragweed is an annual weed that produces thousands of seeds per plant, which can result in severe allergic reactions in humans and animals. The weed can be found throughout the country and it grows in various soil types. In agricultural fields, it can quickly dominate cropland and is difficult to eradicate due to its ability to spread seed and rhizomes. It can be controlled with the use of herbicides and other cultural practices.
Like all plants, ragweed requires light to germinate and grow. It is one of the first summer annual species to emerge in spring. The temperature and moisture of the soil affects germination and growth, as does its latitude. Ecotypes found at lower latitudes are larger and flower later in the season.
The first step in controlling ragweed is to manage its seed production. This can be done by mowing regularly. A mowing schedule that includes cutting the plants when they are 4-6 inches tall will reduce the population significantly for the entire season. Depending on the weather, mowing may need to be performed twice in a season.
Tillage is another important management practice. Aggressive tillage tactics, such as moldboard plowing and inversion tillage, can bury common ragweed seeds below the surface, where they will not germinate. However, shallow tillage tactics can disturb the seedbank and unearth previously buried common ragweed seeds.
A good crop rotation plan also helps to control ragweed. Crops that are planted late in the season or during fall help suppress ragweed by blocking its access to sunlight. Practices that shade the soil, such as cover cropping and narrow row soybean planting, can also enhance ragweed suppression.
Once ragweed plants reach full size, they produce a large amount of pollen. This can irritate the noses and throats of humans, horses, cattle, sheep, dogs and domestic pets. The weed’s pollen can also cause digestive problems. Keeping ragweed at a minimum by managing its seed production is the best way to prevent allergies from this annoying plant.
There are hundreds of herbicide products on the market. Some are selective and kill only certain plants; others, such as glyphosate (Roundup), are non-selective and kill nearly any plant they come into contact with. It is important to read the label and follow all application directions when using herbicides. It is also important to wear the proper personal protective equipment any time herbicides are mixed and applied. This includes jeans and long-sleeve shirts, along with gloves and goggles.
The two most common herbicides used in pastures to control ragweed are 2,4-D and MCPP. Both have low toxicity to livestock but are very toxic to fish and invertebrates. They can deplete dissolved oxygen in water bodies, causing fish or shellfish kills.
When ragweed is young and small, it is easily controlled with good grazing management or mowing. As it grows it becomes more difficult to control. This is when it becomes a major problem for many ranchers and farmers, especially in western Nebraska.
Research and field observations show that a heavy grazing program during late May through June is critical for preventing ragweed problems. It is very effective to use a chemical herbicide after grazing or cutting hay to control seedlings and small plants. Spraying the sward with herbicides such as 2,4-D, Grazon or Curtail can give good season-long control of ragweed. Shredding in September can also help reduce ragweed seed production.
It takes time, a good management strategy and some spraying to control ragweed in pastures but it can be done. It is especially important to get control of weeds early in the spring when they are the easiest to kill, before they set seed.
In addition to preventing ragweed, pastures with healthy grasses provide forage that is high in protein and other nutrients. They also provide a habitat for wildlife, such as deer and turkeys. Western ragweed is an annual that flowers from July through October, producing greenish-yellow fruits with one seed in each “bur.” It provides forage for deer and upland game birds and can be a nuisance to cattle producers.
Whether you’re dealing with common or giant ragweed, there are preventative measures you can take to reduce the likelihood of it making a comeback. These include regular mowing (at least once per season), and improving soil fertility with fertilizer application. Both of these practices are also beneficial in controlling annual weeds like chickweed and mustard, as they tend to grow best in heavy, unfertile soil.
Fertilizers are critical in promoting the growth of cool season grasses and decreasing the competitiveness of weeds such as ragweed, annual winter weeds (like chickweed and mustard) and perennial weeds (like Canada thistle and milkweed). However, applying too much can result in reduced pasture grass production. For this reason, it’s important to use a soil test to determine the correct amount of nitrogen, phosphorus and potassium to apply. The results of the test will provide a guide for how much to apply and when.
In order to get the most out of fertilizer applications, the soil should be lightly grazed or mowed afterward. This promotes tillering and development of a strong root system, which makes it harder for weeds to compete. If you’re using herbicides to control weeds, grazing or mowing shortly after application will also help with weed control.
An ecological approach to weed management involves learning about the biology of problematic weeds and exploiting their weaknesses. This is a more labor intensive process than simply applying herbicide, but it can produce the desired outcome in a more sustainable way. In the video series Manage Weeds on Your Farm, experienced farmers from around the country talk about their success in managing weeds through ecological principles without the use of herbicides.