Delaware County Cooperative Extension

Fall Weed Control Considerations

Fall Weed Control Considerations
Brian C. Pugh, NE Area Agronomy Specialist

Its time to consider fall weed control on pastures that may have become infested with cool season species such as musk thistle, buttercup, red sorrel and curly dock. Every spring and summer, Extension offices receive calls from livestock producers asking us how to get rid of these weeds. Usually when we receive the call, the cool season plants are already at the flowering stage and are expensive and difficult to control. Our best advice at that time is to mow or spray these plants to keep them from going to seed and then treat those pastures the following fall or spring with an herbicide when they are easier to control.

Buttercup
Buttercups are a problem in cool-season grass pastures and easily recognized in early spring by their bright yellow flowers. There are several species of buttercups but all of them tend to emerge in the fall and overwinter as low growing plants (rosettes) that send up stems and then flower in late spring. They are more difficult to control when they are in the flowering stage and producers who have observed them growing in their fields this past spring should consider a late fall herbicide application or a February or March herbicide application. These plants are a lot easier to control during these time periods.
Herbicide applications that work well on buttercups in the rosette stage include; 2,4-D or 2,4-D + Dicamba. After stem growth begins in spring, applications of Grazon, Cimarron max, or Cimarron maybe required.

Dock
Red sorrel, smooth dock and curly dock are three cool season plants that are in the same family and are collectively called sour dock by many producers. These plants tend to be problems in moist pasture situations and are extremely difficult to control when they send up their stems in the spring and begin to produce seeds. They tend to go un-noticed until seed head formation begins but by then, it is usually too late for chemical control. The best times to spray these plants are in November or early March on a day when daytime temperatures are expected to be above 60 degrees. Herbicides that work well during these
two time periods include; 2,4-D, 2,4-D + Dicamba, Grazon next, Grazon P+D, and Cimarron Max. Red sorrel will require a selection of the latter three, stronger herbicides.

Thistles
Thistles are also a cool season weed that can become problematic in spring pastures. There are several species of cool season thistles that inhabit Oklahoma pasture with two of the worst being musk thistle and scotch thistle. These two thistles are considered noxious weeds and should be controlled when identified growing in a pasture. Most of the thistles that grow in Oklahoma pastures will emerge in the fall and overwinter in the rosette stage until late spring when they send up a stalk and initiate flower and seed production. These weeds are easy to control prior to the formation of these stalks but become harder
to control the closer they get to flowering.
Herbicides that work well on thistles when they are in the rosette stage include 2,4-D, Grazon next, Grazon P+D, Cimarron Max, and 2,4-D + Dicamba. The best times to spray these plants are in November or early March on a day when daytime temperatures are expected to be above 60 degrees.

Cool season broadleaf weeds by their nature all tend to be easier to control when they are young and prior to their seed head development. It is easy for these weeds to go un-noticed during the winter and spring only to become a problem in late spring when they send up there reproductive stems and flowers.
Producers, who have had problems with these weeds in their pastures in the past, should consider checking pastures for these winter weeds in Late October and Early November. If large populations are observed, plans should be made to spray these weeds in November or March when the plants are easy to kill. You local county extension office will be able to help you with plant identification and recommend the chemical control option and application rate that will work best for your management system.

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