Early weed control strategies for pastures and hayfields provided

Many pastures and hayfields will become overrun with weeds in late spring. 

Before they get too unruly, producers might want to consider early management options to reduce their presence. 

There have been a lot of questions about how to control weedy annual grasses such as crabgrass, foxtails, panicum, Japanese stiltgrass and others in grass forage settings. Unfortunately, these grasses start germinating at different times in spring, so there are no universal options. 

For example, Japanese stiltgrass can germinate a couple weeks or more before crabgrass and other species. Thus, an early application of pendimethalin will be necessary for initial control. 

Large crabgrass and the other mentioned grasses typically start germinating around 200 growing degree days. 

A great natural sign it is time for a residual herbicide – especially on annual grass – is when forsythia starts blooming. 

Currently, pendimethalin – Prowl H2O and Satellite HydroCap – is an option for controlling annual grasses and broadleaf weeds in cool- and warm-season forage grass settings.

Prowl H2O or Satellite HydroCap can be applied to established perennial forage grasses, including Kentucky bluegrass, bromegrass, tall fescue, orchardgrass, perennial ryegrass, timothy, switchgrass and others, which are grown for forage, greenchop, silage, hay production or livestock grazing. 

Apply at a broadcast rate of 1.1 to 4.2 quarts of product per acre in a single application or sequential applications made 30 or more days apart. 

Herbicides must be applied before weed germination in spring or in-season between cuttings. Otherwise, weeds won’t be controlled. 

These products may be tank-mixed with other labeled herbicides. 

Split applications of pendimethalin are better than a single, high-rate application early in the season. Make the first application – two to three pints an acre – in early spring, around mid-March to early April, but before weed germination. Then, make the second application right after first or second cutting at three to four pints an acre.

One thing to note about pendimethalin is it requires about an inch of rainfall within a week or so after application for it to be activated. If poor weed control is a result, other control tactics might be needed at some point during the season.

Postemergence options are limited 

There are limited postemergence herbicides which selectively control annual grassy weeds without injuring the desirable forage.

Plateau – imazapic – controls crabgrass, foxtails, fall panicum, Japanese stiltgrass and others, including postemergence, when weeds are a few inches tall. However, it can only be safely used on certain cool-season forage grasses. 

Plateau will cause temporary suppression of Kentucky bluegrass, smooth bromegrass, orchardgrass and perennial ryegrass, but it will likely kill tall fescue or timothy.

Facet and Quinstar – quinclorac – do not control Japanese stiltgrass but have some activity on other weedy grasses if they are less than two inches tall. It will kill clovers.

Milestone at five to seven fluid ounces an acre – or other aminopyralid products, GrazonNext HL or Chaparral – provides suppression of Japanese stiltgrass when small – less than six inches tall – and controls several other broadleaf weeds, but it will injure or kill forage legumes. 

When using aminopyralid-containing products, consideration must be given to issues with herbicide residues in the forage and manure which can cause subsequent problems.

Keep in mind pendimethalin products do not control established perennials like roughstalk bluegrass, which is becoming more of a problem in forage fields. Fall and early spring are the best times to apply effective herbicides to control this weed. Unfortunately, there are no effective products to control it in cool-season grass forages. 

In alfalfa settings, the use of Gramoxone/paraquat, Raptor or Select/clethodim after first cutting generally provides 85 to 90 percent control of roughstalk bluegrass.

Scout for winter annuals and biennials

Now is the time to scout grass pastures and hayfields for winter annuals and biennial weeds. 

Winter annuals include the mustard species yellow rocket and shepherdspurse, common chickweed, horseweed or marestail, deadnettle, henbit and fleabane. 

Biennials including bull, musk and plumeless thistle; burdock; poison hemlock; wild carrot and more should be treated before they begin to bolt, and the smaller the better. 

Late fall or early spring is the best time to treat biennials when they are still in the rosette growth stage. 

An effective herbicide application for both will prevent flowering and seed production. 

Perennial broadleaf weeds

Management of perennial broadleaf weeds such as dandelion, Canada thistle, horsenettle, hemp dogbane, milkweed and smooth bedstraw, as well as woody perennials like multiflora rose and autumn olive, can start a little later in early summer, after plants reach the bud-to-bloom stage. 

The most common herbicides for grass hay and pasture this time of year are the plant growth regulator herbicides such as 2,4-D, plus dicamba like Clarity; triclopyr products like Crossbow and Remedy Ultra and clopyralid like Stinger and PastureGard. 

In addition, products containing metsulfuron like Cimarron or other generic formulations can provide good control of many broadleaf weeds in spring. 

A newer herbicide to consider for grass stands which include white clover is NovaGraz from Corteva. It preserves white clover but controls many common broadleaf weeds. However, it tends to be weak on many of the problem perennials mentioned above. 

Also, be cautious if forage grasses were recently seeded and are not yet established as many of these herbicides can cause severe crop injury. 

When it comes to controlling buttercup, it’s important to remember if pastures are yellow with buttercup flowers, it’s too late to get effective control from herbicides. The best time to apply herbicides is from mid-March through April. 

Herbicides 2,4-D at two to three pints an acre; one quart of 2,4-D plus one pint dicamba; 0.2 to 0.3 ounces of metsulfuron/MSM; 24 to 48 fluid ounces of NovaGraz or two to three quarts of Crossbow are commonly used to control buttercup.

When biennials such as poison hemlock, burdock and bull thistle are flowering and a few feet tall, herbicide applications are not effective. As biennials, they form a rosette in the fall, and herbicide applications are most effective when they are sprayed in fall in the rosette stage or before bolting in spring. 

Effective herbicides for biennials include 2,4-D plus dicamba; Crossbow; 24 to 48 fluid ounces of NovaGraz or glyphosate as a spot treatment. 

Dwight Lingenfelter is an Extension associate of weed science with Pennsylvania State University Cooperative Extension. He can be reached at dwight@psu.edu. This article was originally published by American Agriculturist on March 10.