Managing Signalgrass Begins With Proper Identification October 28, 2014 By Todd Lowe

Patches of signalgrass and crabgrass can closely resemble each other in bermudagrass turf but can be properly identified by their seedhead. The seedhead on the left is from tropical signalgrass. The seedhead on the right is from crabgrass.

Weed control, or lack thereof, has been a common topic discussed during many Course Consulting Service visits. It stands to reason that weed control would be an important issue following the rainfall patterns that have occurred in many areas throughout Florida. Scheduling herbicide treatments is difficult during rainy periods and, with some golf facilities recording more than 15 inches of rainfall in September, it is understandable that weeds are prominent on golf courses at this time.

A variety of grassy weeds, sedges and broadleaves have been observed during recent Course Consulting Service visits, but tropical signalgrass has been the most commonly observed weed. Florida golf courses recently lost a valuable tool for managing tropical signalgrass: MSMA. MSMA was an inexpensive herbicide that selectively controlled many weeds in bermudagrass turf. Furthermore, it was the only effective herbicide for controlling tropical signalgrass. It has taken several years to find a replacement for MSMA, but weed scientists at Clemson University recently identified several herbicide programs for successfully controlling tropical signalgrass in bermudagrass turf (see Tropical Signalgrass Control). While these new programs are impressive, so too are their costs and golf course superintendents must plan accordingly.

Another factor that has led to poor signalgrass control has been misidentification, as patches of tropical signalgrass closely resemble crabgrass. Crabgrass is easily controlled with a variety of herbicides whereas signalgrass is not. A misdiagnosis can lead to poor weed control. To properly identify signalgrass, you must locate its seedhead. Crabgrass has a seedhead that has several stalks emanating from a single point and appears much like a hand. Signalgrass, however, derives its name from the fact that its seed stalks occur at 90-degree angles and resemble signal flags.

Source: Todd Lowe,

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