Forage Weeds: Fall Forgotten and Spring Startups

Alyssa Essman, OSU Extension State Specialist, Weed Science
Christine Gelley, OSU Extension Educator ANR, Noble County
Kyle Verhoff, OSU Extension Educator ANR, Defiance County

Spring means rapid forage growth, but it also means rapid weed growth. Due to the variability of spring weather, there are often only a few opportunities to control emerging summer annual weeds, winter annuals missed in the fall, and biennials that are small enough to effectively control. To manage weeds before they become a problem in forages, it is important to scout and plan accordingly. Forage is a broad category, and the spring weed control plan can look very different between species and operations. The problem weeds and whether control is necessary are going to be different between permanent pasture systems and alfalfa fields, and highly dependent on the consequences of specific weeds.

In established alfalfa, the decision for weed control of some winter annuals like henbit and field pennycress will depend on the severity of the weed presence, the age of the stand, and the end purpose of the forage. If the weed pressure is high, the stand is young, or the lower forage quality of the weeds interferes with the goal of producing dairy-quality hay, the weed control treatment may be worth the associated cost. In a grazing system, it may be more pertinent to control weeds in the spring to ensure weeds that aren’t grazed don’t go to seed. Numerous weeds can be a problem in forage systems. Reference the 2024 Weed Control Guide for specific recommendations following this general overview.

Summer annuals are most effectively controlled when they are small in the spring. An example weed is common cocklebur, a summer annual that is competitive in forage stands. The seeds of common cocklebur are toxic to livestock and maintain toxicity when cut as part of hay.

In established pastures, there are many effective control options for summer annual broadleaf control, including:

  • 2,4-D
  • Crossbow
  • PastureGard
  • GrazonNext
Common Cocklebur

Image Source: Iowa State Extension – Common Cocklebur Seedling)

Winter annual weeds are most effectively controlled in the fall when they are small and have not lived through the winter, but there is a window in the spring to control anything missed. A winter annual that is always a concern come spring is cressleaf groundsel, due to its toxicity to livestock. Cressleaf groundsel should be actively managed; if an infestation builds up to where mature weeds with yellow flowers are visible, herbicide control is no longer an option, and the weed maintains its toxicity even after cut. The first cutting of an area heavily infested with common groundsel will likely have to be discarded instead of sold or fed. There are limited herbicide options for control; in pastures and grass hay fields 2,4-D is an effective choice, but will kill any desired legumes present. Weeds can commonly be seen as pretty flowers by neighbors and left to bloom, be sure to scout property edges to lower the risk of a weed infestation jumping into the field the following spring.

In alfalfa and legume hay, some of the chemical control options include:

  • 2,4-DB (Butyrac)
  • Pursuit
  • Raptor
  • Glyphosate (Roundup Ready alfalfa or spot treatment only)
Cressleaf Groundsel

(Image Source: Ohio State Weed Science – Cressleaf Groundsel)

Another group of weeds that we have a chance to control in the spring are biennials. Poison hemlock is a biennial that commonly finds its way into forages, moving in from field edges and fence rows. Poison hemlock is toxic when ingested by livestock and can also cause skin irritation. Poison hemlock is most often a problem in pasture systems that are overgrazed and where there is inadequate grass growth. Where other grazing options are available, animals tend to avoid this plant, but control of poison hemlock should still be a priority. Being biennial, it is most effective to control poison hemlock while it is in the rosette stage.

For the control of poison hemlock in pasture systems, herbicide options include:

  • Remedy Ultra
  • Crossbow
  • Dicamba

Poison Hemlock

All the previous examples given were broadleaf weeds, but there is also the opportunity to control grass weeds in alfalfa and legume fields in early spring. Roundup Ready alfalfa makes glyphosate and products such as Extreme an option. In conventional alfalfa fields, products containing clethodim (Arrow, Select Max, etc.) and Poast are effective at controlling grass weeds.  Weed control in forages is highly situational; it is important to read the herbicide label to ensure effective weed control, limit potential damage to desired forages, and to be aware of any potential grazing or harvest restrictions.

Extra Resources:

Managing Cressleaf Groundsel OSU Video

Poison Hemlock OSU Video