Pasture Weed Management.

 By Glenn Detweiler Area Agent. Agriculture - Livestock N.C. Cooperative Extension. Catawba County Center

 Why control weeds? First, a weed is a plant growing in a place where you do not want it to grow. In pastures and hayfields, it is impossible to have a “pure” stand of grass; there will always be plants that volunteer from the seed bank or from neighboring fields. Therefore, it is important to control weeds to an acceptable level because (1) they can reduce yield and quality of desired plant species and (2) interfere with hay drying. Weeds also (3) have the potential to cause injury or death to livestock if the weed plants are toxic.

What are the steps to consider in controlling them?
Step 1 is to always ID the weeds. This is the most important step, in weed control. This will allow you to determine if they need to be controlled. Take time to walk through your fields and scout at least 10 to 15 sites in a field. Identify the plants and seedlings at each site. It is usually easier to do this between seasons and about a week or two after cutting or grazing. Be sure to keep a record of what weeds you have in each field and when you start seeing them. This will help you determine whether your control program is working. Some weeds may take several years to get under control.      
Step 2 is the preventing the spread of weeds. Many weeds are easily spread. Prevention is any action you take to keep weeds from getting established in your pasture. Many weeds are spread by seeds that are dispersed by hay bales, plants that reach maturity (don’t let that happen), livestock movements, equipment (particularly mowing equipment), wind, water, and wildlife. Another way of introducing weed seed is through planting grass seed contaminated with other seeds; therefore, use certified seed!
Step 3 is cultural control.  Remember to manage for your specific grass. TAKE SOIL TESTS for the ENTIRE PASTURE. Cultural control increases the competitiveness of forage. Provide for proper fertilization by using soil test to determine pH, fertility, and recommended fertility needs for the species of grass you are growing. Then you can take advantage of additional cultural methods to help manage weeds.  One sample is usually good for up to 5 acres if the entire area has the same soil types, same crop, and has had the same practices done to it (fertilizing/liming/etc.). A single sample will consist of at least 12 cores or sub-samples combined together (composite sample). Collect the cores in a plastic bucket, mix, and fill your sample box with this composite sample.   Make the recommended corrections based on soil test results. Grazing management in pastures can help control weeds.
Rotational grazing helps to control weeds by giving desired plants the opportunity to rest and grow undisturbed before being grazed again. In rotational grazing systems, animals will often consume weeds they would avoid in continuous grazing systems.
Mechanical control, primarily mowing, will help control some weeds especially broadleaf weeds. Negative aspects are cost of mowing (fuel and time), it may not help with larger weeds, and it can spread weed seeds and encourage greater infestation. If there is no chemical control labeled for a particular weed or if weeds are too mature, mowing may be your only choice. Always mow at the proper height! In some cases burning, when safe and permitted, may control some weeds in forages.
Weed wiping is another relatively new concept of non-selective weed control for use late in the growing season. It is based on the principle of wiping (or brushing) a nonselective herbicide directly onto unwanted tall weed plants that stand above crops and pastures. Wick wipers, as they were then called, first became available in the 1980s, but never sold in marketable quantities.
They had poor chemical regulation systems that in many cases restricted the chemical application to target plants. Chemical delivery to the wick was by gravity feed and because of the lack of feed regulation or control, the wicks suffered problems of chemical starvation in heavy infestation work when chemical replenishment to the wick was not quick enough or sufficient.  Generally speaking, early "wick wipers" were considered to have limited working widths to hold appeal for broadacre application.
 But since those early units, their design has changed dramatically. Now called weed wipers, most provide accurate regulation of the herbicide placement and application rate, and are available in working widths that make them suitable for broadacre crop and pasture work. The weed wipers available today can generally be divided into about five categories:
• Sponge wipers
• Rotary/roller
• Rope wipers
• Brush
• PVC piping and canvas
Step 4 is Biological control is the use of natural systems to suppress weeds. As a newer approach to weed management, there is much still to be learned. This is generally a longer term approach. It includes the use of natural agents such as plants, herbivores, or insects to suppress weeds. Biological control is usually not complete and may take several years to become sufficiently effective
Step 5 is Chemical Control. Considerations for choosing an herbicide include: (1) Correct identification of weed. (2) Type of pasture/forage. (3) Animal species. (4) Post-application restrictions. (5) Carryover. There are many decisions involved with the use of herbicides, beginning with the correct ID of the weeds present, familiarity with the weed type (grass or broadleaf, annual or biennial or perennial, cool season or warm season), followed by choice of herbicide and determining the correct timing and rate of application. Spot-spraying specific weeds may be the most effective and least costly. For some herbicides there are restrictions for grazing animals. There may also be haying restrictions. Always read and follow label directions and pay attention to any grazing and haying restrictions. The label is the law!
Many farmers and home gardeners have reported damage to vegetable and flower crops after applying horse or livestock manure, compost, hay, or grass clippings to the soil. The damage was caused by residues from herbicide products that belonging to the class of herbicides known as pyridine carboxylic acids. These herbicides can remain active for extended periods of time even after passing through an animal’s digestive tract, to be found in urine, manure, and composting! The label on each of these herbicides contains detailed instructions, including animal feeding restrictions and safe use of manure or crop residues. When used as directed, these herbicides should not cause problems on non-target plants. Follow label directions listed under Carryover Injury to vegetable and flower crops. Proper timing of herbicide application cannot be overemphasized.
The best way to control weeds post-emergence with herbicides is when the weeds have germinated, are young, and are actively growing. This time varies according to whether the weeds are cool season or warm season. As the name implies, warm-season weeds are those that grow during the summer months. The best time to control warm-season weeds with herbicides, therefore, is from April to mid-July for most species. Cool-season weeds grow best in late fall through early spring. The best time to control cool season weeds with herbicides is from October through December.
Weed management takes a focused commitment that includes education, research and implementation of a well thought out strategy.  Farmers and Ranchers who commit to an overall managed pasture and grazing plan will see financial benefit.