Invasive weeds, like other weeds, are plants growing where they don’t belong. However invasive weeds can invade and outcompete other plants in natural landscapes. Invasive weeds are not native to our province and so lack natural enemies. They usually have unique adaptations, or characteristics, that allow them to spread. Some examples of invasive weeds in Saskatchewan are common tansy, common burdock, baby’s breath, absinthe, and leafy spurge. These weeds have advantages over native and forage plants so they can displace desirable vegetation and decrease forage production.
Once established invasive weeds can be difficult to manage. Some of the things that can complicate invasive weed management are land quality, mixed vegetation, perennial plants, and herbivore interactions. Often pastures are on lower-quality soils with challenging topography which limits the use of weed management tools like cultivation and some herbicides. In both natural and seeded landscapes, we often have a mixture of vegetation that includes grasses and forbs, so there are limited herbicide options. Herbicides may end up damaging off-target plants. These landscapes also consist of mostly perennial plants, which are expensive and time-consuming to terminate and re-establish. Domestic livestock and other animals generally avoid weeds and consume more desirable vegetation. This gives the weeds a further advantage over surrounding vegetation and facilitates their spread. Established weeds are challenging to manage and can easily spread and create even bigger problems in more places. Therefore, prevention is easier and more cost-effective than delayed management.
There are many ways to help prevent the spread of invasive weeds. Weeds can be spread in bales, on equipment, in soil or gravel, and by cattle and other animals. Weed-free feed is ideal, but bales that might have weeds can be fed in areas where weeds can be easily monitored and controlled. When moving animals from weedy areas give them a chance to clean out before moving them to a new pasture and watch for weeds like burdock that stick to their hides. Weed seeds can be spread in soil and plant biomass on equipment and vehicles so try to clean up before going to a new area.
Another aspect of weed prevention is preventing opportunities for weeds to establish. Healthy pastures are competitive and can help to prevent weed seeds from ever getting established. Although it won’t prevent all establishment, a healthy plant stand has minimal bare ground and few unclaimed resources which limits the chances that new weeds can germinate and establish themselves. Some of the keys to maintaining a healthy pasture include leaving sufficient litter cover and allowing plants sufficient rest for root growth. Preventing weed establishment is only one of many benefits of keeping a healthy pasture stand.
Even if prevention is unsuccessful, it is still best to be proactive and control weeds as soon as possible. It is easiest and cheapest to manage weeds while they are just a few plants in a small area. Once they spread, they are more expensive to control. Prevention and proactive responses can help to keep weed management costs low and keep the landscape beautiful and productive. For more info on invasive weed management contact your local Range Management Extension Specialist.