Weed Eating Biomachines: How Grazing Livestock can Help Control Invasive Weeds

        In any good weed control program there are some basic steps that should be followed. In general, these steps are:

1)      Identify the weed

2)      Research and consider potential control options

3)      Choose control options and make a plan

4)      Implement weed control plan

5)      Track results and modify treatments as necessary

6)      Maintain weed population control through monitoring and continued control efforts

If one of the control options for your weed is grazing, you have to add one more step…choose the right species! Each species of livestock is unique and their individual characteristics must be considered as part of an effective targeted grazing program.

What is targeted grazing?

        Targeted grazing is defined as: “the application of a specific kind of livestock at a determined season, duration, and intensity to accomplish defined vegetation or landscape goals” (Launchbaugh and Walker, 2006). In other words, targeted grazing uses the impact of livestock grazing a plant to manage vegetation. Targeted grazing extends beyond weed control and can also include fire fuel management and habitat management. This article, however, will focus on the weed control aspect of targeted grazing.

Grazers, browsers, and everything in between

        A grazer is an animal that prefers to eat grass species. Horses and cows are generally considered grazers. Sheep are considered intermediate feeders because they tend to prefer forbs (broadleaf plants) over grasses, however, they readily eat both types of plants. Browsers are animals that prefer to eat shrubs; goats are considered browsers. While each species has definite preferences regarding the types of plants they prefer to eat if given the choice, they can all learn to eat other types of plants, especially if they are introduced to them at a young age.

Choosing the right species for your job

        The species most commonly associated with targeted grazing are cattle, sheep, and goats; cattle are the largest of the three species. When considering which species to choose it is important to consider the overall height of the animal and also mouth design. Cattle have a relatively large muzzle and they use their tongue as a foraging tool. They wrap their tongue around the plant they want to eat, draw the plant material into their mouth and then use their lower teeth pressed against their upper dental pad to pinch or tear the vegetation off of the rooted portion of the plant. Because of their larger size and greater height, cattle can reach vegetation sheep may not be able to and they can also provide greater animal impact in the form of crushing and stomping unwanted vegetation when they are held at tight enough densities. The large rumen in cattle also allows them to consume and process large amounts of low quality forage.

        Sheep and goats have smaller mouths which allow greater ability to select individual plants and plant parts. Sheep and goats can graze a plant and eat only the flowers, or strip the leaves off the stem. In one study conducted in Idaho, goats were used to control yellow starthistle. The goats were turned out late one year and the yellow starthistle had already entered the ‘spiny' stage. Researchers watched as the goats moved through the paddock and ate almost every spiny starthistle flower first. Once the bulk of the flowers had been consumed, the goats moved back through the paddock and proceeded to strip the leaves off the stem of the starthistle plants. The grazing treatment significantly reduced seedset and further, by removing the leaves, the goats reduced the ability of the plant to recover and potentially set seed a second time that season.

Viability of seeds post-digestion

        The main goal of any good weed control program should be to significantly reduce seedset. Under that premise, the viability of seeds after passing through a ruminant digestive tract is an important topic to consider. Viability of seeds after being digested is hard to predict because so many factors related to both seed characteristics and digestive function of each ruminant species must be considered. However, a general rule that less than 50% of seeds survive can be assumed with a fair amount of certainty. In the case of yellow starthistle seed viability post digestion was between 2 and 8%. If there is any concern with animals transporting viable seed via feces to uninfested areas, a holding period of 4 to 7 days is recommended.

Final thoughts

        When considering which species to choose for any weed control job, the goal should be to match site and plant characteristics to animal ability. Factors such as percent slope, palatability of target species, and growth form of target species are important and should be taken into consideration. Additionally, some weeds may be poisonous to some species of livestock. When planning a targeted grazing program there are many factors to consider and experienced targeted grazing practitioners can help match animal ability, age, pen size, and duration of treatment to individual goals and situations.

        It's important to remember that using livestock as a weed control tool also requires consideration of proper animal care and husbandry. Weed eating biomachines cannot be put on a shelf until the next job is ready. They need food and water 24/7/365. Be prepared to work with your livestock owner to meet animal needs and be flexible. Additionally, be prepared for the unexpected, animals have a way of surprising us.

        For more information contact Julie at: 661-868-6219 or via email at: jafinzel@ucanr.edu.

References:

Launchbaugh and Walker. 2006. Targeted Grazing: A natural approach to vegetation management and landscape enhancement. American Sheep Industry Assocation.

Goehring, B.J., K.L. Launchbaugh, and L.M. Wilson. 2010. Late-season targeted grazing of yellow starthistle (Centaurea solstitialis) with goats in Idaho. Invasive Plant Science and Management. 3(2): 148-154

Goehring, B.J. 2009. Effects of targeted grazing of yellow starthistle by domestic goats in northern Idaho and an examination of seed survival in the ruminant digestive tract. M.S. Thesis. University of Idaho, Moscow.