These weeds may cause producers problems by causing death or injury to livestock in extreme cases or, more commonly, by limiting our forage production by stealing the resources the grass would otherwise use.

Weeds are always referred to as any plant growing out of place. The most common types of weeds forage producers strive to control are herbaceous broadleaf weeds. In other areas, the very grasses we are trying to grow in pastures are considered weeds when they try to take over the flowerbed or grow in the cracks on the driveway.

This constant pressure of broadleaf weeds has created the field of weed science and has fascinated and occupied many weed scientists for years – and will continue to as weeds continue to evolve over time. This has also created a need for forage producers to develop a plan to manage broadleaf weeds in a way that optimizes forage production.

Controlling these noxious weeds can be accomplished by using many different methods. Weed management methods typically consist of mechanical and chemical means. In some cases, biological control can be used as a method to control weeds.

The methods you select will depend on the weed species present, size of area infested with weeds, the density of the infestation and the budget you are willing to allocate toward weed control.

Mowing has limitations

A common weed control practice is shredding or mowing a pasture. The first shredders made their way into pasture usage in the 1950s and are still commonly used as a weed control method today. While shredders do an excellent job of removing the tops of weeds, these machines come with a lot of additional negative baggage.

When compared to spraying an herbicide for weed control, shredding is the most expensive method. While many annual weeds can be controlled by removing the top and preventing development and seed release, the perennial weeds will continue to grow after being mowed.

While mowing, you also lose many pounds of forage production due to the shredders’ inability to be selective between a broadleaf weed and a desirable grass.

Another negative aspect of shredders is the many different re-sprouting brush species. When the top is removed, a single-stem brush plant comes back with vengeance, multiplying the number of stems and making it more difficult to control later. The bottom line is: Shredding or mowing as a method of weed control offers a clean-looking pasture for a small window of time but has little other value.

Multispecies grazing as control

Biological weed control is a method some forage producers make work; however, this comes with its own sets of problems as well as a few benefits. A common method of biological control is to graze sheep or goats, whose diet consists of a higher percentage of forbs and browse than cattle diets.

One of the benefits of this method is: Running another species of livestock will become another profitable enterprise and the broadleaf weeds that were a nuisance are now a desirable food source. However, there are a lot of problems that can come with this, some of them involving fences, predation, parasites and, potentially, the need for more labor.

Chemical control

The most commonly used weed control method is chemical, accomplished by using herbicides. This has been a common practice since the invention of 2,4-D that was released in the 1940s and is still a commonly used active ingredient today, either by itself or mixed with other active ingredients.

Herbicides today are applied through a variety of methods starting from the ground going up to large-scale aerial applications. Many small do-it-yourself sprayers are mounted on ATVs that may contain boom or bloomless nozzles.

On the other end of the spectrum, larger ground rigs such as TerraGators may be used which have the capacity to treat 200-plus acres with one load. Aerial application using an airplane or helicopter is also a very common method in weed control.

Some of the benefits are being able to treat large number of acres within a short period of time and being able to apply where a ground rig would not be able to access due to topography, muddy conditions or tall brush that would cause difficulty for a ground applicator to work through or around.

The type of herbicide you select to treat weeds will depend on your location to be treated, type of forage program and type of weeds you are trying to control. A common way to split up herbicides is to classify them as those with residual activity and those without.

Residual activity occurs if herbicides persist in the soil after they are sprayed, continuing to provide some level of weed control. Non-residual herbicides will control what is up and growing at the time of application but will not persist in the soil after application.

Some common active ingredients that have residual activity are aminopyralid, picloram and metsulfuron methyl. Active ingredients that do not possess residual activity are 2,4-D, triclopyr and fluroxypyr. Another factor to consider when using herbicides that contain aminopyralid or picloram is whether or not there will be any composting of the forage or using manure from livestock that has consumed forage treated with these actives.

A common problem with these ingredients is: They remain active for a long period of time as well as remaining active in the manure of a cow that has consumed forage treated with herbicides that contain these ingredients. For example, if you fertilize with cow manure from a cow that consumed forage treated with one of these actives, then the manure will have the opposite effect of the desired outcome – fertilizing.

Application points

Other things to consider when treating noxious weeds are timing of application, type of weed you are treating, gallons of spray solution per acre, surfactants and type of nozzle/droplet you are using. The timing of application will influence the outcome of your weed treatment. As a rule of thumb, treat annual weeds when small, about 4 to 6 inches in height.

Perennials weeds typically need to be treated while they are flowering, in most cases. The type of nozzle and droplet size you use also has a role in what your outcome will be. For example, a small flat fan nozzle will emit very fine droplets that will provide excellent coverage; however, these are also more likely to drift, thus increasing the likelihood of off-target damage.

A bigger droplet will be less likely to drift but will also not provide the coverage small, fine droplets will. When using a bloomless nozzle, such as a boom buster or boom jet, the droplet size will increase as you get to the end of the swath in order for the nozzle to be able to throw the solution the distance larger droplets are needed. While this is still a very effective nozzle, it will not provide the even distribution of a boom-type sprayer.

In summary, in controlling noxious weeds, whether they are harmful, poisonous or very unpleasant, there are many variables and factors forage producers need to consider before deciding what method is appropriate. When weed control is applied correctly, your returns will be weed-free pastures as well as an increase in forage production for that year. If you have questions about weed management in your area, ask the local county extension agent for assistance.  

PHOTO: Mowing is not enough. Multispecies grazing may help. And chemical use is prevalent. Controlling noxious brush and weeds, however, demands a multipronged approach. Photo by Lynn Jaynes.

James Jackson is the extension program specialist at Texas A&M AgriLife. Email James Jackson.