Perennial Weed Management

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Modified from Dwight Lingenfelter and Bill Curran, Penn State

Perennial broadleaf weeds are seldom controlled with soil-applied herbicides and are best targeted with postemergence application. Canada thistle, the bindweeds, horsenettle, hemp dogbane, milkweed, and pokeweed are some of the more common perennial species. One challenge for successful management is targeting herbicide application when these perennials are more susceptible to a systemic herbicide. In general, applications at bud to bloom or later in the summer are most effective, and this can be difficult to achieve, particularly in corn. Systemic herbicide application in soybean, following small grain harvest, or in grass hay or pasture can be more effective than earlier in the summer. Herbicide options in soybean are few and Roundup Ready technology with glyphosate is an important tool for perennial weed management. Glyphosate rates for perennial control are generally at the upper end of the rate range; refer to specific glyphosate labels for appropriate rate. In corn and grass hay, the plant growth regulator herbicides (Group 4) become important choices in situations where these products are appropriate. Below is a quick summary for the herbicide effectiveness on perennial broadleaf weeds.

Herbicide Effectiveness on Perennial Broadleaf Weeds

N = none; 6 = 55-65%; 7 = 65-755’ 8 = 75-85%; 9=85-95% control.