Weed Management on Small Sheep Acreages (2012)

Bring successful Weed Control to Smaller Acreages
The majority of sheep in the Fraser Valley are raised on small areas of between 5 to 15 acres. Most of these are subdivided into smaller paddocks. This set up, and a reduced amount of specialized equipment compared to larger livestock operations, makes for a different approach to weed management.

Canada thistle, blackberries, and bog grass (a sedge) may be the weeds most likely to present persistent problems, but there are many others.

"Prevention, prevention, prevention" emphasized Dr Linda Wilson from the Ministry of Agriculture in Abbotsford, talking about weed control. "Know your weeds, and how they grow, and get on to them early. Think of the competition between your desired forage and the weeds, and suppress them without killing off the grass. With the unwanted plants removed, the surrounding grass is able to bloom up and outwards, not only giving you more forage, but allowing the grasses to be strong competitors against the weeds that are constantly wanting to gain a foothold." This reduces future weed growth by shading and the removal of other nutrients from the soil.

Vegetation Management
"Whether you are using fertilizers and herbicides, or are taking an organic approach, you want to manage your fields to the advantage of the grass or your desired forage, and to the disadvantage of the weeds," she continued. "Ongoing management of the vegetation is essential for long-term, sustainable pasture health and performance."

She explained that sheep themselves like to eat some of the broad leafed weeds and, under some circumstances, can be taught to eat weeds they previously would not touch. But not all of them.

Wilson should know - she conducted a 3 year experiment on sheep clearing land of yellowstar thistle in Idaho many years ago. In BC, sheep were used for years to feed on all green growth trying to crowd out newly planted tree seedlings.

David Ralph , Weed Technologist for BC , from the Ministry of Forests, Lands and Natural Resources Operations, in Kamloops agreed with her."

"If you are renovating your pasture, test your soil, find out its pH, and what the forage you are growing needs, and try to provide those nutrients - whether lime, major or micro nutrients," he advised.  "This will help keep the desired grasses healthy and growing well".  This in turn reduces bare patches which allow for chance germination from windblown seeds, or an opportune place for an underground root or runner to sprout.

More work with organics
The organic approach, which excludes the use of synthetic fertilizers and herbicides, works better for some weeds than others, although it nearly always involves a lot more work. Setting things up for the desired forage to grow well, preventing weed growth in the first place, and quickly getting on top of it, is even more important.

The timing of herbicide application is important. "After the first light frost, but before a killing frost, is a good time to apply herbicide on Canada thistle and blackberries," Ralph advises. "This first mild frost stimulates the plant to transfer all its nutrients down quickly to its root system, so a herbicide is translocated more effectively at this time." Other weeds are best controlled by herbicides applied when the weeds are young and actively growing, such as in the spring or early summer.

Some plants dug right up to the bottom of its tap root, could be controlled this way. Plants with a fibrous root system like bog grass, which likes wet areas that most grasses don't, if tilled every 5 to 6 weeks, throughout one summer might be controlled this way in one season, especially if combined with improved drainage - again optimizing the conditions the grass likes, and eliminating the conditions that sedges thrive in.

Organic acetic acid
Acetic acid, a component of household vinegar, is showing some promise as an organic herbicide if derived from organic sources, but not if derived from chemicals. It is more effective on mature and extremely problematic plants at higher concentrations than that found in vinegar. It kills most vegetation in a few hours by drawing moisture out of the leaf.

There are several selective herbicides available for use on weeds.

Both specialists recommended using a selective broad leafed herbicide such as Milestone, an aminopyralide based weed killer or - their one of choice for effectiveness - the often disliked, even feared, 2-4,D neither of which will affect grass growth. The ultimate objective is to optimize grass growth, give it a chance to get going, and to fill in bare patches.

If you use a non selective herbicide such as acetic acid or RoundUp you kill everything, including what you want to grow, and it seems, are soon back to square one.

Commenting on the toxicity of 2-4,D versus RoundUp, Ralph observed that while one dose of 2-4,D is the more toxic of the two, it may only have to be applied once a year for a few years to eliminate a weed, whereas RoundUp might have to be used 2 to 3 times a year, every year, depending on the weed in question. After a few years the problem should be eliminated with a broadleafed herbicide, whereas RoundUp will kill everything it touches and probably end up being used on an ongoing basis. "So the cumulative effects of the latter may be the worse of the two, and you end up with a clean pasture with 2-4,D.

"Read the label, always wear protective clothing, and follow the instructions that come with each product' advised Ralph.

Wipe-on applicator
He notes one way to reduce the quantity of a herbicide used to the bare minimum on small patches of weeds, is the use of a hand held wipe-on applicator. This would be too labour intensive for large areas, but would work for some people on smaller farms. This wand like tool, shaped like a hockey stick with a soft footed cloth soaked in herbicide, is brushed over the target weed only, reducing contact with other plants or the soil, and may be the best compromise to eliminate problem weeds while minimizing unwanted environmental side effects.

"Mowing Canada thistle regularly before flowering, say about every 5 to 6 weeks, reduces the casual germination of wind blown seed, but not an underground spreading root system." he continued. Cut up roots from tillage may also germinate on their own, multiplying the problem. Blackberries throw out runners which easily take root in receptive soils and are again difficult to control organically.

Both specialists were pessimistic about the sustainable control of Canada thistle and Brambles using an organic approach. "I have not seen tillage work successfully with thistles," observed Ralph. Digging up large areas of thistles to the extent needed is usually impractical. "Digging up the plant to at least 2 inches below the crown will give you a good chance, but not total elimination. There is a similar problem with blackberries unless the area affected is very small.

Article by Jo Sleigh, published in May 2012 edition of Country Life in BC