By Blake Jackson
Managing perennial weeds in grass pastures and hayfields requires the right combination of timing, mowing, and herbicide applications, according to Penn State Extension Weed Specialist Dwight Lingenfelter.
Many producers focus on spraying weeds during the summer, late summer and fall are generally the most effective seasons for long-term control.
As temperatures begin to cool, perennial weeds naturally move sugars and nutrients from their leaves into underground roots and rhizomes to prepare for winter.
Applying systemic herbicides during this period allows the products to travel into the root system, providing better control and reducing regrowth the following season. Effective herbicides include products containing 2,4-D, dicamba, triclopyr, glyphosate, or metsulfuron.
To improve herbicide performance, producers should mow pastures or hayfields earlier in the growing season to prevent weeds from producing seeds.
After mowing, weeds should be allowed to regrow to about 12 to 15 inches tall before treatment, typically four to six weeks later.
In most areas, the ideal application window runs from early September through October, although timing may vary depending on local conditions and weed species.
Different perennial weeds respond best to specific herbicides. Canada thistle, horsenettle, hemp dogbane, milkweed, multiflora rose, quackgrass, and smooth bedstraw often require targeted products or herbicide combinations for effective control.
Permanent pastures may also benefit from products such as GrazonNext HL or GrazonPD3, while glyphosate spot treatments can help manage weeds like Johnsongrass and quackgrass.
Lingenfelter also advises combining herbicides with liquid nitrogen fertilizer during hot, dry weather because the mixture can severely burn forage crops and reduce productivity. Applying fertilizer and herbicides separately is the safer approach.
Weed wiper applicators can be useful when broadcast spraying is not practical, although they generally provide less effective control than broadcast or spot applications and may require repeated treatments.
Before using any herbicide, producers should carefully read the product label and follow all grazing and haying restrictions, as waiting periods vary by product, livestock type, and whether forage will be grazed or harvested for hay.
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Categories: Pennsylvania, General