Weed Management

Managing Forages and Animals to Prevent Weeds

The best way to prevent weeds in a pasture is to keep the ground covered. Invasive weed species only appear in forage systems when there are available resources and space. 

Match Stocking Rate to Available Forage

Stocking rate decisions should be made based on forage availability. Stocking rate refers to the number of animals being grazed within a given system over a defined period. Stocking too high leads to shorter rest periods and overgrazed forage thus increasing the likely of plant death and open soil. If we need to decrease the stocking rate on a farm, options will include:

1. Purchasing more land
2. Purchasing more hay and supplemental feed
3. Selling animals

There is no target or textbook value for stocking rate. Practically, stocking rates should vary throughout the year to match available forage resources with the forage demand of the grazing animals. For more information, please see UGA Extension Bulletin B1568 Understanding Stocking Rate in Pasture Systems.

Protect Your Rest Periods

Rest is critical for stand longevity and resiliency in forage systems. Forages require time between defoliation events to restore root carbohydrates that were depleted during regrowth. Defoliation events refer to grazing or harvest events. The plant will pull carbohydrates from the roots to initiate regrowth after the leaves are removed until photosynthesis begins again. Failure to allow adequate rest will result in plant death and open ground.

Protect Your Residual Forage

Residual forage is critically important to the stand’s resiliency and regrowth rate. Residual forage refers to the stubble that is left behind after the animals have grazed the pasture or the forage has been harvested for hay or baleage. This material is needed for photosynthesis after the defoliation. The more residual forage we can leave behind, the faster the canopy will regrow which limits opportunities for weeds to move in.

Keep Soil Fertility Balanced

A balanced soil fertility program is critical to stand longevity and economical sustainability of forage-based production systems. Soil fertility can affect yield, carrying capacity, forage persistence, resistance to stress, nutritive value, and many other aspects of the production system. It is important for plant health and stand longevity to keep these nutrients in balance. Otherwise, the invasive species will take advantage of these nutrient imbalances and deficiencies.

Keep Soil pH Near Neutral

Soil pH affects many soil properties including nutrient availability, soil structure, soil biological activity, and potential for aluminum toxicity. Many soils in Georgia are acidic (low pH; below 6.0), but it is possible for soils to be too basic (high pH; above 7.0). Ideally the soil pH should be between 6.0 and 7.0 to optimize forage production and give our desirable forage species a competitive advantage over invasive weeds.

Manage Insects

Although we cannot control when insects show up, we should strive to limit their impact on our forage systems. Two of the most detrimental insects to our pastures and hayfields are the fall armyworm (Spodoptera frugiperda) and the bermudagrass stem maggot (Atherigona reversura). Both pests will leave the grass stressed and more vulnerable to weed invasions.

Use Correct Species and Varieties

Recommended species and varieties are chosen based on their proven production and longevity in a specific environment. While some may temporarily grow under our climatic conditions, they may not perform reliably across multiple seasons. Furthermore, some species establish quite well in Georgia but may not provide a good return on the investment because of low production capabilities (e.g. one annual grazing event or short-lived perennials). Please check with your local county Extension agent and our website for updated recommendations prior to making planting decisions.

Tips for Identifying Weeds

Routine scouting of fields can help limit the spread of invasive weed species. Don’t assume all green grass is good! Pay attention to areas that are left ungrazed by livestock and watch for unique seedheads. Spot treatment is often the only solution to controlling invasive species, so we need to identify them as early as possible.

Resources to Help with Species Identification

Your local County Extension Agent will be an excellent resource to help with identifying plant species in your pastures and hayfields. Additional resources can be found online at state Extension service websites, Extension publications, or digital tools such as smart cell phone applications that use artificial intelligence to identify pests almost instantaneously.

While these digital tools are excellent resources and can serve as a starting place for successful species identification, they are under constant development and may require additional confirmation. Identification is only as good as the images we put into the application.

Important Plant Parts for Species Identification

Some plant species are unique and can be easily identified from a single picture of the entire plant. Unfortunately, many of the invasive species discussed in this bulletin, especially grasses, require additional pictures for identification. Possible pictures may need to include:

1.       Entire plant

2.      Leaf margin (edge)

3.      Where leaf connects to stem (critical for grass identification)

4.      Seed head or flower

5.      Roots

How to Take Better Pictures

One of the most common challenges in taking good pictures is ensuring the plant is in focus. This can be challenging in forage systems since the weed species are often similar shapes and colors as our desirable forage species. Cut or dig the plant you need to identify and place it on a solid background for the picture. Any solid color object is sufficient: side of a vehicle, tailgate or cargo area of a vehicle, or even a solid color coat or shirt.

Common Weed Species

Weed pressure is just one of the many factors impacting forage quantity or quality. Overgrazed pastures, poorly managed hayfields, and low fertility soils are extremely prone to weed invasion once the desirable species start to recede. There are three main categories that most weed species will normally fall into when discussing their impact in established forage systems.

These categories are not all-inclusive. They do not account for sedges, forbs, trees, or other functional groups that may be found in pastures and hayfields. However, these three categories cover many producer concerns in an average forage production season.

Annual Broadleaf Species

Annual broadleaf species are very common. These include species such as pigweeds, mare’s tail, and dogfennel. Fortunately, there are ample options for controlling these species in established grass pastures and hayfields.

Annual Grass Species

Annual grasses have both pros and cons. Species such as crabgrass provide good grazing potential but is considered a noxious species in hayfields because it slows dry down. Alternatively, species such as goosegrass or yellow foxtail provides little feed value under either management system. These species are best controlled with pre-emergence herbicides because there are few selective products available for post-emergence control.

Perennial Grass Species

Perennial grasses are the most problematic category of weeds that forage producers must deal with. These include species such as vaseygrass, knotroot foxtail, and smutgrass. Many of these are rhizomatous or have expansive root systems that make them difficult to control. There are virtually no selective chemical control options for these species in perennial grass forage systems. Therefore, prevention is critical!

Chemical Control Recommendations

General Herbicide Recommendations

Read the herbicide label carefully before applying the product. Always double check the rate, timing, and stage of growth of the weed and desirable plant species.

• Annual broadleaf weeds should be controlled at 2 to 4 inches tall.
• Annual grasses are most easily controlled with pre-emergent products.
• Rhizomatous weeds and plants with deep root systems are best controlled in early fall.
• Sedges are nearly impossible to control with herbicides, consider cultural control options.
• Small trees and shrubs are much easier to control than large ones.

Pesticides are listed in the Georgia Pest Control Handbook. This resource is updated annually to reflect new products and label changes. Always refer to the specific product label before applying an herbicide to your pasture or hayfield.

Links to Specific Herbicide Recommendations

• Vaseygrass
• Knotroot Foxtail
• Johnsongrass
• Smutgrass: coming soon!

Note on Pesticide Use

It is important to always read any pesticide label before use. Use the product strictly according to the label directions. It is particularly important to follow all safety precautions. Trade and brand names are used only for information. The University of Georgia does not guarantee nor warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others, which may also be suitable.