General Weed Management Information

Serious weed management issues in pastures are a symptom of a problem with the crop or site. These problems can include grazing methods, fertilization programs, forage species selection, and irrigation or water management.

Land used for grazing livestock will not warrant the major expense required for herbicide use or other methods to control weeds, in many scenarios. It is usually more appropriate to look for ways to manage the forage and the site to prevent or reduce weed problems. Changing the grazing methods, fertilization, forage species, and water management will change the competitive balance in favor of the forage rather than the weeds, in many cases.

Healthy and well-established forage plants are more likely to resist weed invasions. Therefore, manage desirable forage species to make them as competitive as possible with weeds. The areas around gates, water troughs, feed bunks, bedding grounds, roadways, and fence lines should be the first to receive attention, because forage plants are sparse there and the soil is disturbed frequently. Weeds often first become established in these spots; then, it is much easier for them to spread out to grazing land. It is not practical to completely stop disturbing the soil, but reseeding a competitive grass can make the sites much less inviting to weed invasion. If it is not practical or economical to overseed an entire pasture, consider seeding livestock trails and reseeding both sides of roadways, since this is where weeds are likely to show up first.

Pastures can be made more competitive against weeds by taking reasonable measures to promote the forage. This is crop management, not weed management. Controlling weeds does not necessarily mean an increase in forage yield. As a general rule, every unit of weeds produced reduces forage by an equivalent amount. If available resources are used to make the crop grow better, a yield increase can be expected, and the impact of weeds should be reduced. It is important to carefully select the forage species and variety for the site and the objectives. Then fertility, soil pH, irrigation or drainage, grazing management, mowing, and periodic overseeding all have potential to influence crop growth and the ability of the forage to compete with weeds.

When forage deteriorates to the point that corrective measures must be taken, the question is how to best correct the situation. If tillage is feasible, it is tempting to start over by plowing or disking, to prepare a new seedbed for a pasture. This may be the best alternative, but more often it exposes many new weed seeds to an environment that favors their germination. The land is out of forage production for several months, and nothing has been done to prevent further deterioration under this management scenario. Increased soil erosion and the relatively high cost are additional disadvantages of complete pasture renovation.

It may be better to simply overseed the pasture by the most suitable method. Several types of no-till planters and techniques may be appropriate. If the seed is simply broadcast on the soil surface it will help to irrigate, run livestock over the field for a few days, or harrow and then pack or roll the field to move the seed into contact with the soil. Broadcast seeding spreads the forage seed over the entire pasture area, which should be more competitive with the weeds than drilling in rows. However, no-till planting in rows offers the obvious advantages of not taking the field out of production for a long period, and creating little soil disturbance that would expose new weed seeds to conditions that favor their germination. Increasing the seeding rate of the forage by approximately 30% is recommended when using the broadcast method.

In areas inaccessible to machinery, it may be appropriate to feed seeds of desirable species to the livestock so the seed will be planted after passing through the animals. Certain grasses and most small-seeded legumes remain viable after going through an animal’s digestive system.

There are times when direct action to manage weeds is advisable. Some examples of these situations are provided below.

  1. Weeds that are new to a farm or property and few in number should be controlled with a shovel, herbicide, or other appropriate method, before populations become well-established.
  2. Poisonous plants can cause unacceptable livestock losses. Implement control programs in grazing areas that are small enough and accessible. Fencing might be appropriate in serious cases, but herbicides or shovels are good tools if plants are widespread and relatively few. Poisonous plants frequently are the first to appear in spring. Delay introducing livestock into these areas until adequate forage is available, then do not overgraze. For more information on pasture management and poisonous plants, access the Oregon State University Small Farms website:
  3. Certain perennial weeds—such as Himalayan blackberry, Canada thistle, leafy spurge, field bindweed, and quackgrass—cannot be discouraged by competition from vigorous forage plants. Herbicides, physical removal, or tillage are common control methods for these species, but consider grazing different livestock, such as goats or sheep, which may provide effective control.
  4. If weeds have become so dense and the forage species so thin that the site is unprofitable, using herbicides or tillage may be the best management option. This should be done only when necessary.

When attempting to reduce weeds in small pastures, direct management and resources to promote growth of forage species so they will be better able to compete with the weeds. This concept is helpful in correcting certain weed problems and in slowing or preventing invasion of new weed species. Careful use of herbicides can be a useful tool for forage management. In terms of overall importance, livestock management follows closely behind management of the forage sites. The best chemical for forage production is probably fertilizer.

When herbicide use is justified, being able to buy products in the small quantities needed can be a problem. Do not buy more product than needed for the current year, when possible, because secure storage of the extra herbicide will be needed.

Below is a partial listing of some of the herbicide products available to effectively manage weeds in small pastures. This list changes continuously and herbicide brand names come and go; always refer to the active ingredients in this list when purchasing a product to apply to your pasture.