Smooth and Downy Brome Identification and Control

In the early spring before Kentucky bluegrass breaks dormancy and after Kentucky bluegrass shut down for the season in the fall, smooth brome stands out as a course textured patch in your lawn, sod farm, golf course rough, or sports field. During the growing season, its color and texture are comparable to Kentucky bluegrass and is not as much of a nuisance.  

Both brome species (Smooth and Downy) can act as weeds in high quality turf areas. Smooth brome has many desirable characteristics to function as a useful turfgrass species; however, its poor density limits the use to low-maintenance areas. 

There are several identification traits distinguishing brome grass from many other weeds. The sheath is nearly closed, giving it a V-neck sweater appearance. Brome has a rolled vernation, hairy sheaths and blades as well as a distinctive “watermark” (or W-shaped) on its leaves as seen below in Photo 1.  Its spindly-natured leaves, small membranous ligule, and winter annual growth habit can usually identify Downy brome. Brome spreads rapidly by its extension rhizome system and its seeds are often carried by wind/birds from low maintenance areas to well-maintained turf. 

There is no guaranteed selective control for Smooth brome in Kentucky bluegrass, creeping bentgrass, or perennial ryegrass turf. Early research from Zac Reicher and Matt Sousek at the University of Nebraska has shown earlier year application (June) rather than (July) will aid in Tenacity control of smooth brome in Kentucky bluegrass. This study will be replicated in 2014 and further data will be passed along as available. Downy brome can be controlled with the preemergence herbicide Siduron and post-emergent Sethoxydim (only for use in established fine fescue stands; tall fescue slightly tolerant).

In most cases, a nonselective, systemic herbicide should be used and multiple applications may be needed to effectively control brome grass. 

Photo 1: Smooth bromegrass’s v-neck sheath and “w-shaped” watermark at midway point of leaf blade. Photo courtesy of Stephen K. Barnhart, Iowa State Press (1997).

 

Photo 2. Picture of Downy brome taken this week at the ISU research station. You can see the v-neck sheath as well as fine hairs.

When do I apply my Crabgrass Preventer?

A key to the successful control of annual grasses (such as crabgrass) in established turf is the correct application timing of preemergence herbicides. Preemergence herbicides should be applied by May 1^st in central Iowa. Dr. Christians has noticed that this date does not vary much from year to year, after monitoring germination dates for the last 34 years.

 

In addition to timing: application uniformity, using recommended product rates, and the requirement of (1/2 inch) irrigation within 3-5 days of application can play a vital role in crabgrass control. 

Several products are available for effective annual grass emergence control. These products vary slightly in mode of action, length of control, specific weed efficacy, desired turfgrass seed inhibition, and early postemergence control. Benefin, benefin + trifluralin, bensulide, oxadiazon, siduron, pendimethalin, mesotrione, prodiamine, isoxaben, and dithiopyr are preemergence products available in the market today. 

Please note that some products are not labeled for certain turfgrass species. For example, oxadiazon is not recommended for use in fine fescue; however, oxadiazon provides   excellent goosegrass control in Kentucky bluegrass. Always read thoroughly and follow the label directions. Remember, the label is the law.

Dithiopyr and prodiamine have the longest window of effectiveness and can control weeds for up to 16 weeks. Dithiopyr and mesotrione offer early postemergence control when applications are made following weed emergence. Siduron and mesotrione have a unique property that allows herbicide application to seeded areas. Siduron selectively controls weedy annual grasses such as crabgrass, foxtail, and barnyardgrass, while allowing the desired turfgrasses to grow.  Mesotrione is only labeled for preemergent use on newly seeded Kentucky bluegrass lawns. All of the other preemergent herbicides kill the seeds of the cool-season grasses and cannot be used at the time of seeding.

Fertilizer-herbicide combinations are sold at most retail stores. This allows homeowners to combine the two operations into one application. A disadvantage of the combination is that the proper time for weed control often does not coincide with the optimum time to fertilize. Combinations with preemergence herbicides are generally effective in controlling annual grass weeds as long as applications are made at the appropriate time and recommended amount.

In addition to annual grassy weeds, a spring application of a preemergence herbicide will control annual broadleaf weeds, such as prostrate knotweed and spurge. A second application at a reduced rate may be necessary for season-long control. 

Paying attention to herbicide timing, application uniformity, product and rate, and ensuring (1/2 inch) irrigation within 3-5 days of application will help prevent annual grass (crabgrass) invasion. Below you will see two pictures of crabgrass in an early leaf-stages.

The last picture is a general guide of preemergence application dates via Quali-Pro's Prodiamine label: