By: Sarah Sommerfeld, PAg, Regional Forage Specialist, Saskatchewan Ministry of Agriculture
Adoption of weed management strategies for forage stands can be a valuable tool. Weeds often associated with forage stands are plants that are perennial, aggressive growing and hard to control. Such plants can include Canada thistle, foxtail barley, dandelion, leafy spurge, absinthe wormwood, and common tansy. As weed infestations increase in size and severity, the cost of control increases and the production of desirable forage declines. Management and control of weeds begins with field scouting and identification.
Scouting for weeds in forage stands should occur regularly. Scouting helps determine if undesirable plants are present. Scouting also identifies conditions which favour the development of a weed infestation. Poor plant competition from desirable forages, bare soil or any other type of soil disturbance can lead to a weed problem. If any of these conditions are present, the next step is to determine the cause.
The grazing management of a pasture can point to a potential cause of a weed infestation. Overgrazing of desired forage plants leads to plants that are less vigorous and productive. Overgrazing also leads to a reduction in pasture litter carryover and an increase in bare soil. Litter is the amount and distribution of dead plant material. Litter helps to reduce surface evaporation and conserves moisture. Litter also protects the soil from erosion and maintains soil stability. A combination of less productive forage plants, a reduction in litter carryover and an increase in bare soil can make for the right situation for the invasion of hard to control weeds.
Pastures are not the only forage stands that are susceptible to weed invasion. Lack of management on hay stands can have a similar result. Depleted soil fertility and improper cut timing results in less vigorous forage plants and potential weed invasion.
A weed problem will always have a cause. Effective long term weed control requires identification of the weed itself, and the cause of the problem. To implement an effective weed management strategy, action must be taken to ensure the cause of the problem is addressed.
Scouting for new weeds is best done when they are easiest to identify, often in the month of June, prior to seed set. Correct identification of the weed is necessary to select the most effective control method. Consult with an agrologist or local weed inspector for assistance in weed identification or to discuss the best control method. When considering a control method, be aware of the environment surrounding the problem area. For example, applying the herbicide picloram which has long term residual soil activity and high water solubility, is not permitted near open water, wetlands or on soils with shallow aquifers.
Monitoring the area for effective control following treatment is important. If adequate control has not been achieved, an alternative control measures should be undertaken. Reasons for a lack of effective control should be determined and corrected for future reference.
For more information on scouting for weeds in forage stands and perennial weed control, contact your local Regional Forage Specialist or the Agriculture Knowledge Centre at 1-866-457-2377.