Weed Management in Pastures

So, What's the Problem with Weeds?

Pasture diversity is good, but:

• Weeds tend to be more competitive than the desirable pasture plants
• Weeds are generally lower in feed quality, both crude protein and digestibility, particularly as they mature
• Some weeds can be very toxic to livestock. Toxicity is generally not an issue unless there is little else for the cattle to eat
• Some weeds are not palatable due to thorns, bristles, or hairs on the leaves and stems
• When weeds are not consumed by livestock, it allows the weeds the opportunity to reproduce and spread
• There are no threshold numbers for weed management. It is difficult to determine at what weed density the most economical time to control them is.

Here's a Little Education on Life Cycles of Weeds

It is essential to understand how weeds grow in order to effectively target their control. The purpose of plants is to reproduce. They can be annuals, biennials, or perennials.

• An annual completes its life cycle in one year. The seed sprouts, grows into a plant, flowers, and goes to seed, then dies. The plant will be eliminated, but it could have produced hundreds, if not thousands, of seeds in its lifetime. An example is lambsquarters. It is also considered a summer annual. A winter annual begins its life cycle in the fall, survives the winter, and flowers and produces seeds in the spring. Chickweed is a winter annual.
• Biennials complete their life cycles in 2 years. They will grow vegetatively the first year and produce flowers and seeds the following year. Common burdock is an example.
• Perennials will live longer than 2 years, flowering and producing seeds every year. Think of dandelions.

Weeds can reproduce in ways other than seeds. Some produce tubers, or bulbs, like wild garlic. Quackgrass has rhizomes, which are underground stems, as a means of reproduction. There are weeds that have above-ground stems called stolons.

Let's Take a Look at Control

The old saying, an ounce of prevention is worth a pound of cure works with weeds.

Check the Fertility and pH

Get a soil test done on your pastures. Some weeds prefer more acidic soils. Apply lime and fertilize as needed to maintain healthy and growing pasture plants. This will help them compete with the weeds.

Mowing or Clipping

This is done after the livestock graze and before the weeds produce seeds. This works well for weeds where the flower stem elongates, like wild carrot and common burdock. It may take several clippings per year for a few years to get some weeds under control.

Overseeding

This adds plants to the pasture without renovation. It can be done to fill in thin or bare spots with desirable plants before the weeds fill in. Seeding works well in late winter with legumes, especially clovers. Seeding then is called frostseeding. The freeze-thaw cycle will bring the seed into good contact with the soil, increasing the germination rate. The entire pasture can be frostseeded with legumes, which provide nitrogen from the root nodules to feed the grass.

Pasture Rotation

By giving pastures a rest period, they can recover more quickly from grazing. Rotation also reduces the likelihood of overgrazing, which can lead to bare spots or weakened plants.

Biological Control Practices

These can help with weed management. There are some host-specific insects and diseases that will slow down the growth of weeds. Alternative livestock or multispecies grazing can control some weeds as well. Goats or horses may eat weeds that cattle won't. This is not practical unless you already have other species on the farm, or you can borrow some goats!

Chemical Weed Control

Options for pasture weed control are limited. A producer must choose what type of weeds to eliminate - either broadleaf or grass weeds. Generally, most pastures are predominantly grasses, so broadleaf control is the choice. Unfortunately, chemical control will also eliminate legumes, such as clovers and alfalfa. If this is the option, overseeding or frost seeding may be done afterward. 2, 4-D products work well since they are applied, absorbed by the leaves, and translocated in the plants. Make sure to follow the label instructions and check for grazing restrictions. For specific recommendations, contact your local extension office or check out the links for your state. Timing is critical for control. Annuals are most easily controlled in the seedling stage; biennials prior to flowering; and perennials in the bud or early flowering stage. Growing conditions affect the effectiveness of herbicides. Droughty conditions toughen the cuticles on weeds, making absorption more difficult. Pay attention to weather conditions, as rainfall soon after application will dilute or wash off the herbicide.

The Best Approach to Weed Control is the Integrated Approach

Maintaining healthy pastures is the first step. Rotation is an excellent management practice to allow pastures to rest. Fertilize as needed and clip to reduce the spread of weed seeds. Use herbicides wisely. Try spot treatment with herbicides for smaller patches, before they become widespread.

Prepared by Nancy Glazier, Cornell Cooperative Extension, and John Comerford, retired Penn State Faculty. Part of a joint project with Pennsylvania and New York, funded by NESARE