The word “weed” is defined as “a valueless, troublesome plant growing wild, especially one that crowds or damages the desired crop.” It is likely that all of us have a few weeds growing in our pastures. Maybe more than a few.
But before you go killing everything that isn’t a blade of grass, J.D. Green, PhD, and James R. Martin, PhD, from the University of Kentucky’s department of agronomy and cooperative extension service, remind us that some weeds actually provide good nutrition for horses. For example, dandelions are high in beta-carotene, and many horses find them quite tasty.
Still, most weeds are invasive and some are even toxic, so controlling them is advisable. There are a variety of methods available to do so, and various factors to consider. Here we will look at how to best manage the weeds so your pastures remains lush and nutritious.
Types of Weeds
It is first a good idea to become familiar with weeds common to your area. There are many books and Internet sites full of detailed pictures and descriptions. Contacting your local extension office is also helpful. Common broadleaf weeds compete directly with forage grasses, and they reduce the nutritional value and longevity of the pasture. Perennial and biennial are the worst because they persist for many years. Perennials such as thistle, dogbane, and multi-flora rose reproduce from seeds and via underground structures, which makes them difficult to eradicate. It is best to devise a long-term plan that utilizes prevention, eradication and control.
Preventing weeds is the first line of defense. This can be done in new areas by planting high-quality grass seed and keeping any weeds that crop up from going to seed (which is the only way annuals and biannuals reproduce). Eradication involves completely removing existing weeds, but removing one weed could create space for another type. It is best to eradicate in small patches 10 to 100 feet in diameter to avoid becoming overwhelmed. Control means keeping the weeds at a manageable level, and it is the most commonly used strategy. The following are the four methods of control:
1) Cultural. This involves promoting the growth of desirable plants through proper fertilization, irrigation and soil testing. The best weed control is a strong, actively growing stand of grass, and the worst weed control is allowing pastures to be overgrazed to the point where there is mostly dirt. Perennial, sod-forming grasses compete best with weeds, and if you are putting down new grass seed, make sure that it is weed-free. Adjusting the soil pH and nutrient levels will help establish grass, but at the same time could also be beneficial to weeds. Kentucky’s cooperative extension service recommends the following for ideal pasture management:
- Maintain proper soil pH and fertility levels.
- Use controlled grazing practices.
- Mow at proper timing and stage of maturity.
- Allow new grass to become well established before use.
- Renovate pastures when needed.
2) Mechanical. This is the oldest and most common method. It consists of mowing, tilling, hoeing and hand pulling. Mowing before weeds mature will decrease or prevent seed production. Green says that the ideal height is 12 to 18 inches for most weeds, and they should be clipped as close to the ground as possible. Frequent mowing over 3 to 5 years can deplete the root stores of perennial weeds like Johnson Grass and horsenettle.
3) Biological. An insect or disease that is a weed’s natural enemy can be introduced. Livestock, particularly goats, can also be effective weed control if they are not allowed to overgraze the pastures.
4) Chemical. Herbicides will kill weeds, but they should always be used judiciously. It is important to always read and follow the label directions and safety precautions. Extension services recommend that they be used only when necessary, utilizing the proper dosage and timing. It is also important to be aware of any residue laws in your area, which can be determined by contacting your local state extension agent.
There are many different herbicides available, but the broadleaf variety are the most common, because they kill the weeds while leaving the grass. Keep in mind, however, that broadleaf herbicides will also wipe out any clover in the pasture. Stephen Hart, PhD, extension specialist in weed science at Rutgers University, lists Ally, 2,4-D, Banvel, Crossbow, Stinger, Spike and Weed Master as broadleaf herbicides that can be safely used on grass pastures. Banvel and 2,4-D are absorbed by plant leaves and transferred to roots. Thus, they need to be used when plants are growing. Ally works well on multi-flora rose, but grasses need to be well established. Ally stays in the soil and shouldn’t be used if you plan to seed pastures in the next year or two. Stinger is good for thistle and marestail, but is not effective on many other pasture weeds. Round-Up is a non-selective herbicide (meaning it will kill everything), so it is best used as a spot treatment.
The timing of herbicide application is based on the stage of weed growth, the potential risk to nearby crops, air temperature and humidity. Perennials are most susceptible during early bloom; annuals are vulnerable during the active growth stage when they are small. Green and Martin state that the ideal temperature is over 60 degrees for several days before and after application. They say that while most broadleaf herbicides do not have grazing restrictions, the general practice is to keep horses off the pasture for 7 to 14 days. The exception to this rule is Round-Up, where horses should be kept out of pastures for 14 days if used as a spot treatment and 56 days if the entire pasture is treated.
Take Home Message
Chances are if you have pastures, you have weeds, and typically you can only hope to contain them. Most extension services recommend utilizing at least two different methods for best all-around control. Regardless, it takes a constant effort to keep weeds at a minimum, but it’s an effort for which your grass (and thus your horses) will thank you.
Fortunately, most toxic plants are not very palatable to horses. Generally, they will leave the plants alone unless the pasture has become so depleted of grass that they have little else to eat. Types of poisonous plants vary depending on what part of the country you live in, so contact your extension specialist to become familiar with common, regional toxic plants. A few common toxic plants are: wild cherry, red maple, locoweed, larkspur, lupine, chokecherry, black locust, and alsike clover. The degree of poisoning depends on the quantity consumed, stage of growth, and time of year. If you even suspect your horse has eaten something poisonous, it is best to contact your veterinarian immediately. —SC