Weed Management in Integrated Crop-Livestock Systems
Many livestock species are uniquely suited for weed management within cropping systems; however, some species damage crops and/or will not forage on weeds. Keys to successful integrated livestock systems include matching crops with compatible livestock and understanding and providing cost-effective infrastructure, including fencing, shelter, and water.
Integrated crop-livestock systems (ICLS) are well-recognized for their invaluable role in productive, resilient, and sustainable agriculture. However, these systems are often poorly managed due to overgrazing, soil compaction, erosion, pathogen contamination, and crop damage. Maintaining crop and soil health while also considering the wellbeing of livestock can be challenging without appropriate knowledge and tools. When well-managed, ICLS can feed the soil food web, boost crop production, and increase both water retention and carbon sequestration. Consider the two meter-thick, rich black soils of historic American grasslands, built up through the grazing and trampling of massive, predator-driven bison herds (Knapp, 1999). In contrast, the precarious condition of soils in the present-day American West was largely caused by a century of continually-grazed sheep and cattle and worsened by fire suppression, habitat fragmentation, and introduced species (Ceballos, 2010).
Integrated Livestock Effects on Crop Systems
- With Good Management:
- Reduce weed pressure on crops
- Reduce need for labor, fuel, and agrochemicals to manage weeds
- Improve soil through added nitrogen, phosphorus, potassium, and organic matter
- Diversified farm revenue streams
- With Poor Management:
- Crop damage
- Soil compaction, reduced water retention, and more run-off
- Pressure on palatable forage species reduces competition for the most problematic weed species like cheatgrass, thistle, red stem filaree, etc.
- Increased labor and infrastructure costs for managing stock
The primary conclusion of our research project is that weed management varies drastically depending on livestock species, breed, and age. Livestock must be rotated intensively to significantly impact weed pressure within a cropping system, replacing hand-weeding or herbicide use. This rotation often requires more labor than it saves; therefore, in smaller scale integrated systems, livestock are rarely the most cost-effective way to manage weeds. However, if livestock provide other valuable benefits to justify their expense, weed management can be a positive side effect.
When grazing poultry, we found it difficult to predict which types of birds would forage aggressively on weeds and which species or breeds would be ineffective. We recommend viewing any poultry-induced weed reduction as an added benefit, without depending on them as the primary weed management strategy. In our experiments, runner ducks - universally considered to be excellent grass weeders - showed little interest in consuming any weeds in our vineyard, even when grain-based feed was drastically limited to encourage more foraging. The young birds consumed some grape leaves but lost interest in foraging on vegetation (including weeds) after 8 weeks of age, for unknown reasons. For three years in a row, turkeys minimally foraged on clover and tender grasses in the orchard, and they ignored windfall apples. Red ranger chickens showed brief interest in weed foraging, but only between 7 and 9 weeks of age. Cornish cross broilers demonstrated no interest, reducing weeds slightly - not by eating them - but by sitting on them. As expected, laying hens proved better weeders than all three types of broilers, but they also did significantly more damage to young trees by girdling and attempting to roost in them. Geese took a clear first place amongst the poultry types for weeding prowess. They consistently ate all weeds (with the exception of thistles) in their study plots - often right down to the dirt. Geese were also easy to fence and were resistant to predators (due to their size and aggressiveness).
Ruminants are more reliable weed foragers than poultry, and the sheep in our study consistently consumed a large quantity of orchard weeds. They also browsed heavily on lower apple branches and grape vines up to about 4.5 feet. With standard and semi-standard fruit trees, a single round of browsing did not appear to significantly impact harvest. However, weeds in a spray-irrigated orchard such as this one require cutting or grazing multiple times per season, so this assault on the lower branches could easily add up to costly dents in production.
Additionally, if not grazed rotationally in small pens, sheep and other ruminants are unlikely to eat weeds evenly and will focus on their preferred food sources while letting more problematic weeds flourish. If left to continually graze in a large area, grazers will return to certain sections repeatedly, focusing on the high-nutrient new growth while neglecting other sections that will mature and become too fibrousand unpalatable and will ultimately go to seed. For maintaining a living ground cover, a balance of grazing and rest will optimize productivity, grow resilient roots, and continue to compete against weeds in the ecosystem. Continual grazing stresses the desirable plants while giving a competitive advantage to the more noxious weed species.
When rotationally grazed in an orchard, sheep (or other ruminants) will thrive on most grass and forb species but may need some encouragement to eat the less palatable weeds (like mature knapweed) without losing weight. After their preferred forage is grazed, offering supplemental protein through a tub or block can encourage more even weed removal. While prolonging grazing in a section can increase consumption of unpalatable weeds, paddocks should be sized so that animals are moved before the desirable forage plants produce new shoots (usually every 7 days in the growing season), as grazing regrowth depletes vital root resources.
Toxic and Unpalatable Weeds:
It is essential to know your local weeds to best strategize how to manage them. It often seems to be the case that the most problematic or noxious weeds are the ones our livestock are least willing to graze! And whatever they tell you about “goats eating anything,” the worst weeds are usually the very last thing to get grazed, only after all the more desirable species have been removed. Fortunately, some unpalatable weeds are palatable during certain life phases, while others are palatable to some livestock species and not others. Sheep can be encouraged to graze knapweed, especially early in the season. The window for grazing cheatgrass is incredibly short in the early spring, but because it is one of the first plants to sprout, many grazers will consume it when contained in the area. There are also methods to make less preferable plants more palatable. For example, spraying thistles with salt water can encourage sheep and goats to forage. Mixing target weed species with animal feed for several days to a week before introducing animals to a weedy pasture can also instill some enthusiasm for clearing the problem plants. Weeds like leafy spurge, spotted knapweed, dalmatian toadflax, mustard, and thistle have high in protein and overall nutrition if grazers can be taught to tolerate the higher tannins these plants contain.
Some weeds cannot be safely or effectively managed by livestock, and other strategies are recommended (such as burning, solarizing, spraying, tillage, or ecosystem approaches). In some cases, livestock can be trained to avoid crops or poisonous plants, generally by using a nauseating compound like lithium chloride to give them a negative association. These methods can be effective, but they may not be reliable. If one animal in a flock or herd starts eating the non-target species again and receives positive nutritional signals, the entire flock can quickly return to dangerous grazing behavior. Training may need to be repeated at intervals depending on how inquisitive individual flocks and animals are with eating risky foods. Utah State University has more information on aversion training.
This NRCS publication lists toxic weeds in Montana and Wyoming, starting on page 21. Some toxic weeds of particular concern in the Bitterroot Valley include:
- Hoary Alyssum
- Field Pennycress
* If you are unsure if a plant on your property is poisonous, contact your local County Extension or submit a sample to the Montana State University Schutter Diagnostic Laboratory for analysis.
Understanding Grazing Behavior
Some universal basics of grazing behavior will affect how livestock perform:
- Grazers and browsers eat the most palatable plant species before moving on to the
less palatable ones. This often means that animals consume desireable grasses and
forbs while ignoring the target weeds, ultimately giving the weeds an advantage while
stressing valuable forage plants.
- The primary solution is high-intensity rotational grazing, which forces livestock to graze all available plant species while preventing them from re-grazing plants during regrowth
- Grazers will eat short, young, high-protein plants and leaves before moving on to
the more mature, fibrous options like stems and tall grass. They will not graze pasture
evenly if they have enough space to choose. This often leads to a patchwork of overgrazed
short sections and untouched long sections, both resulting in poor forage production.
The plants in the short sections become highly stressed and vulnerable to increased
weeds while long sections go to waste and suffocate the following year’s growth.
- Solutions include rotating stock in small paddocks, timing paddock use so the unwanted plant species are young and tender, grazing in specific parts of the season when desirable forage plants are dormant, or mowing the mature weed species shortly before grazing to provide more palatable regrowth
- Forage that is near other resources (such as shelter, feed, water, shade, minerals)
will get more grazing pressure than forage that is further away, more exposed, or
harder to access. For example, chickens avoid potential danger by staying close to
overhead cover.. Ruminantstend to conserve calories by using the most convenient
feed options. Other reasons that motivate animals to loiter in or to avoid certain
spots include: an increase or decrease in pests (like flies), soil quality and resulting
forage nutrition, and proximity to companions or potential breeding partners.
- Ideally, these motivators can be used to manage grazing pressure. Whenever possible, place shelters, waterers, minerals, scratchers, and feeders in weedy areas to target grazing and trampling. In the winter, hay can be fed in weedy or overgrown areas.
- Areas like riparian zones that naturally get heavy livestock pressure may need extra protection with fencing to keep grazing periods short
Species- and breed-specific traits need to be matched with weed management needs:
Aggressive browsers (e.g., goats) can manage brushy weeds, whereas grazers (e.g., poultry) will consume immature grasses and forbs. Hogs can be useful for ripping out the roots of undesirable plants, while donkeys have an unusual willingness to eat thistles and cattails. Ducks and geese can be remarkably aggressive with quackgrass, while broiler chickens will probably just sit on it. These different types of livestock require very different care and fencing.
Other things to consider when choosing a species and breed are:
- Is there a local and/or accessible market for the product this animal creates at the volume your operation creates it (meat, fiber, eggs, lambs/calves, dairy, etc.)?
- Can your fencing contain this type of animal? The 2-strand hotwire or 600V electric
net that easily contains an experienced ewe is no match for troublesome 3 month-old
- Electric fences need to maintain 800-1000 V of charge to keep most livestock in and serious predators out, yet very few energizers (especially solar ones) can reliably manage this voltage in the face of challenges like wet grass or dry ground. Investing in a very powerful charger (2+ joules) and/or exterior fencing saves lives and many grey hairs!
- Electric fence can do most of the heavy lifting, but certain situations require something sturdier. In addition to weaning and breeding, activities like castrating, vaccinating, trimming, and medicating animals become much safer and more efficient with the proper facilities. Conditions like deep snow or flooding also make a sturdy pen or dry lot essential.
- Hogs may bury the bottom wire and uprooting fence posts
- If needed, can the enterprise cover the expense of upgrading?
- Exceptions include equines and experienced cows or ewes
- Are the necessary services and processing available? This may include a USDA certified processing plant, shipping, feed supplier, mobile sheep shearer, or veterinarian that has the capacity for your herd/flock
- Do you have adequate and food-safe product storage and transport for your products, and does it meet safety standards if you are selling retail or wholesale? See the current USDA Guidelines.
- Do you have winter housing, water, and feed options that won’t break the bank or require
more labor than is available?
- If not, can you raise animals seasonally by growing out or finishing young animals for market, and is there an affordable source for these animals at the right time of the year?
Lockard, E.C. (2008). Effects of Foraging Sequence on the Ability of Lambs to Consume Endophyte-Infected Tall Fescue (Alkaloids), Birdsfoot Trefoil (Tannins), and Alfalfa (Saponins).