Livestock and other beneficial organisms for weed management

B. Frick, E. Johnson - Scott Research Farm

Problem
Many plants considered weeds in agricultural crops are actually highly nutritious and palatable plants. Can livestock use weeds? Can we integrate livestock and other weed eating animals into a weed control strategy?

Background
On mixed farms, livestock may be used directly to graze weeds, or consume mown weeds, chaff, and screenings. Goats are browsers, and are especially good at controlling woody plants, such as aspen or rose. Goats also eat thistles. Sheep can effectively control leafy spurge. Once they acquire a taste for it, sheep consume large quantities of spurge, which gives them nutritious forage. Sheep are especially good for weed control, as they graze close to the ground, and will readily eat thistles. In legume crops, sheep will graze out grassy weeds. Geese have been used in garden plots to control grassy weeds. Weeder geese can be used (at five to six geese/hectare) after crops grow too large for birds to eat. Hogs, at 24 animals/hectare, can control perennial weeds between cropping seasons in fenced fields. Cattle and sheep can be used for early grazing to prevent weed growth. Weed regrowth faces strong competition from legumes and grasses in pasture. If livestock are used to graze mature weeds, or to dispose of screenings or chaff, digestion will destroy many, but not all, weed seeds.

Livestock also have indirect benefits in a weed management system. Livestock reclaim otherwise-useless things like screenings, chaff, patches mown for weed control, and these practices become more viable for the producer.

Long-term rotations that include a perennial offer distinct benefits to soil quality and weed management. Currently, the usual way to get alfalfa or another perennial legume back into the rotation is to include livestock as part of the production system. Options that generate the ‘livestock advantage’ without livestock might also be pursued. For instance, dehy and seed alfalfa producers might develop partnerships with livestock producers.Beneficial creatures other than livestock may also be important in weed management. They can be encouraged by maintaining habitat for them. This might include reducing tillage, maintaining shelterbelts and wooded refuges, sloughs, or borders, and leaving unbroken native land. Blind use of refuge habitats is risky, because it is difficult to determine, at first, if creatures harbored this way are beneficial or harmful. However, careful observation should help make that decision. Our usual habit of viewing all non-domesticated creatures as pests may be cautious, but it is unwarranted.

Biological agents in the soil can also affect competitive relationships among crops and weeds. Some biological agents are available to improve crop growth, such as the rhizobial inoculants used with legumes to support nodulation or the fungal organism of Penicllium billai to solubilize inorganic phosphorus in the soil. Arbuscular mycorrhizae (AM) can benefit plants by facilitating nutrient uptake and improve growth and yield. These mycorrhizae benefit some species such as cereals and legumes over species that do not associate with them, such as wild mustard, lamb’s quarters, wild buckwheat, tame mustard, canola and quinoa.

Other soil organisms can be directly detrimental to weeds. Seed-borne bacteria may effectively reduce dormant weed seed populations. Rhizobacteria have potential to reduce the vigor of grass weeds in cereal crops. Applying microbial agents to control weeds may prove useful in the future. Reducing tillage might foster growth of these bacteria, which actively grow on crop residues, and are favored by the cooler, moister environment the residues generate.

Helpful insects can be encouraged by providing habitat, such as shelterbelts and ground cover. Increased weed seed predation has been observed with cover crops. Reader reported that groundcover restricted seedling emergence by providing a habitat for seed predators. High numbers of insects, snails, slugs, and voles were reported in heavy residues of rye and hairy vetch and it was felt that these organisms’ feeding decreased the number of weed seedlings. Some carabid insects show a preference for species of foxtail.

Conclusions
Livestock can be useful in weed management both as direct consumers of weeds, and because livestock provide cost recovery for some weed management practices such as chaff collection or mowing. Other beneficial organisms can be encouraged by leaving natural environments within the farm ecosystem, by reducing tillage, and by using chemicals judiciously.


Funding
Provided by the Canada-Saskatchewan Agri-Food Innovation Fund


Contact information
Brenda Frick, Ph.D., P.Ag.
Prairie Coordinator
Organic Agriculture Centre of Canada
c/o Department of Plant Sciences
University of Saskatchewan
51 Campus Drive, Saskatoon
Saskatchewan, Canada S7N 5A8
Tel: (306) 966-4975
Fax: (306) 966-5015
Email: brenda.frick@usask.ca


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