Considerations when using herbicides to terminate a stand

Forage Stand Composition

When planning to terminate a forage stand, consider the types of species present, as some termination strategies are more effective than others on individual species. Conventional tillage methods may not be effective at removing forage crops with large crowns or extensive root systems, such as alfalfa and smooth bromegrass, compared to termination strategies that include herbicides. When using herbicides for termination, follow label recommendations and refer to the latest version of The Ministry of Agriculture's Guide to Crop Protection to ensure products are registered for tank-mixing. Always read and follow label recommendations regarding re-cropping intervals and water volume requirements for adequate spray coverage.

For stands dominated by grasses, high rates of glyphosate can be relatively inexpensive and effective. Depending on forage type, apply glyphosate in summer or fall at a rate of 1 to 1.34 litres per acre (540 grams active ingredient per litre formulation). Hard-to-control species such as orchard grass, meadow bromegrass, smooth bromegrass, and meadow fescue may need higher rates for fall application and/or an additional 0.67-1.34 litres of glyphosate per acre in the spring for effective control.

Grass species with very fine leaves such as creeping red fescue and Kentucky bluegrass have very extensive root systems and are difficult to control with glyphosate alone. Regrowth may occur one to two months after glyphosate application and compete with the subsequent crop for light, nutrients and water. A pre-harvest (in-crop) treatment in the subsequent crop may be needed for additional control.

For effective control of stands with a high proportion of legumes, consider tank-mixing glyphosate with 2,4-D or dicamba and applying it at the bud to bloom stage. If there is a mixture of grasses (e.g. quackgrass, bromegrass) and broad-leaved weeds (e.g. Canada thistle, perennial sow-thistle, dandelions), a glyphosate mixture with dicamba or 2,4-D will improve results on broadleaf species.

Grazing or Feeding Restrictions

Grazing or feeding restrictions need to be considered when using herbicides to terminate forage stands. Glyphosate products are the only products registered as a pre-harvest treatment for the termination of forage crops when the forage is to be used for hay or grazing. Other products, such as 2,4-D, are not registered for pre-harvest application on hay forage stands.

In the Guide to Crop Protection, 2,4-D has numerous feeding and grazing restrictions. They include a restriction on harvesting the forage for hay within 30 days of application, a seven-day grazing restriction for lactating dairy animals, and a three-day withdrawal period from treated fields for meat animals before slaughter. It is important to note that the grazing restriction refers to tolerant crops such as wheat or barley when 2,4-D is being applied conventionally as an in-crop weed control in the spring. Because alfalfa and other legumes are the target species when terminating a stand, these restrictions no longer apply. Thus, stands that are terminated with 2,4-D in the tank-mix should not be fed to livestock.

Please refer to the latest version of the Guide to Crop Protection for grazing and/or feeding restrictions.

Re-Cropping Restrictions

When using herbicides to terminate a forage stand, it is important that re-cropping restrictions are considered. For example, 2,4-D has re-cropping restrictions if applied in the year of seeding; however, there are no re-cropping restrictions indicated on the label for any crop the year after treatment Thus, if applying 2,4-D in the spring prior to seeding (spring termination), re-cropping options are limited to wheat, barley and rye. If applied in the previous summer or early fall (September) to terminate a stand, there are no-cropping restrictions the following spring when applied at recommended rates. (Although 2,4-D doesn’t have any labelled re-cropping restrictions when applied in the fall, some research has shown that under dry fall conditions on coarse-textured soils, there may be impact on sensitive crops, such as broadleaf crops, especially as fall 2,4-D rates increase.)

Other herbicides may have longer re-cropping restriction periods after application. Please refer to the latest version of the Guide to Crop Protection and product labels for a complete list of re-cropping restrictions for residual herbicides. There is no registered herbicide to control volunteer perennial forage grasses in spring wheat.