Quintin Johnson, Extension Associate, Weed Science; firstname.lastname@example.org
Fall provides an excellent opportunity for perennial weed management in pasture and hay with herbicide applications. Most herbicides labeled for use in pasture are translocated, or moved, to various parts of the plant. As fall approaches, perennial weeds like curly dock, Canada thistle, horsenettle, pokeweed, and others are beginning to replenish stored carbohydrates in root structures to prepare for over-wintering and new spring growth. Translocated herbicides are able to reach the rooting structures more efficiently during this period, thus providing more effective perennial weed control. However, if weeds are drought-stressed, herbicide translocation may be slower or incomplete, resulting in less effective control. Delay herbicide applications until after you receive adequate rainfall. Fall applications should be made at least 7 to 10 days before a mowing for greatest effectiveness. In well established perennial weed populations, multiple years of good weed control will be needed to significantly reduce the rootstock of perennial weeds.
There are several things that must be considered when choosing an herbicide for pastures or hay fields including: forage species grown; weed species present; risk of herbicide contact with desirable plants through root uptake, drift, or volatility; residues in composted straw or manure; herbicide rotational, over-seeding, grazing, or harvest restrictions; and cost. Be sure to follow all precautions and restrictions on herbicide labels.
The “Pasture and Hay Weed Management Guide” for Delaware is available from the University of Delaware Cooperative Extension. Access a pdf version on-line at http://www.rec.udel.edu/weedscience/WS_ManagementGuides.html.