Superintendent Magazine - March, 2011

COLUMNS

The Control Center: Taking the Quack Out of Quackgrass

Superintendents can battle this pesky weed culturally and chemically. Here's how
By John C. Fech

For grassy weeds, and quackgrass is no exception, the best timing to apply herbicide is when the weeds are first spotted.
PHOTOS BY SYNGENTA / UNIVERSITY OF NEBRASKA/LINCOLN (INSET).

Quackgrass is in a category of tough weeds to control. Until lately, the Roundup and reseed approach was the only real solution other than digging it out with a shovel.

So, what's so wrong with quackgrass? Why can't we just let it be? Unfortunately, the presence of quackgrass introduces a different color and texture to golf course turfgrass. As such, it interrupts the uniformity of the turf, which is problematic for playability and aesthetics.

A more basic reason for its classification as unwanted is that quackgrass competes for water and nutrients. As a result, it causes turf stands to be thinned. Sure, broadleaves such as prostrate knotweed, plantain and dandelions are also objectionable; quackgrass is just a little more subtle about being a pest.

Description and growth pattern


For grassy weeds, and quackgrass is no exception, the best timing to apply herbicide is when the weeds are first spotted. (Inset) In addition to the clasping auricles, the characteristic seedhead of quackgrass helps with identification.
Perennial grasses, in general, can be difficult to identify and distinguish from each other. Several perennial grassy weeds that invade golf courses appear much like each other, including orchard grass and tall fescue. In some situations and growing environments, zoysiagrass and bermudagrass can be mistaken for quackgrass.

Quackgrass can be identified through observation of the following characteristics. First, inspect the auricles that circle the stem of the grass plant. Quackgrass has "clasping" auricles - narrow pieces of tissue that come to a point - that wrap around the stem. Using a common 10x hand lens, the auricles are easy to observe and useful to note in that very few other weeds have this feature. The ligule, a small and thin piece of tissue located at the base of where the leaf attaches to the stem, is short and membranous.

Secondly, quackgrass has a strong and extensive underground spreading habit. Observation of the underground stems (rhizomes) requires excavation. To determine if an unknown weed is quackgrass, use a sod spade to dig up the roots and examine them. If they are connected together by long vining stems, the plant may be quackgrass. Rings of fibrous root hairs occur every inch or so along the rhizomes.

Third, consider the width of the leaf blades. Again, it may be difficult to separate quackgrass from other perennial species. Quackgrass usually contains leaf blades that grow to be about .25 inch wide, whereas tall fescue and orchard grass usually have leaves in the .25 to .5-inch range. The leaf blades are rough on the upper surface.

QUACKGRASS AT A GLANCE


With its origins in Europe, quackgrass (Agropyron repens) is a cool-season, perennial grass that can reach 3.5 feet high. It's naturalized throughout North America as a weed and spreads by creeping rhizomes.

Quackgrass will continue to grow until the roots and shoots have experienced many hard frosts and soil temperatures are consistently below freezing.

Because quackgrass is very aggressive and produces many rhizomes, it can quickly dominate turfgrass. Quackgrass usually contains leaf blades that grow to be about a .25 inch wide. Quackgrass is also known as: couch grass or couch-grass, quitch, twitch, witchgrass, and creeping wheat-grass.

Another useful characteristic is the season of growth, especially in the Northeast, Midwest and Pacific Northwest. Quackgrass is a cool-season perennial; it will continue to grow until the roots and shoots have experienced many hard frosts and soil temperatures are consistently below freezing, compared to zoysiagrass and bermudagrass, which will begin the onset of dormancy after a few hard frosts have been received.

Cultural control

Two main methods of cultural control can be effective. The first is to maintain a thick, dense turf through proper irrigation, fertilization, cultivation, etc. Such a turf will grow vigorously, and be able to successfully compete with quackgrass for light, nutrients and water.

Secondly, the technique of scouting can be helpful. Using a thorough, regular inspection regime, quackgrass can be spotted before it has taken a strong foothold. Isolated patches can be located and marked for removal or spray application.

Monitoring or scouting involves frequent inspections of turf to detect early signs of weed growth. Its primary goal is to detect, identify and describe pest infestations. All turf (and landscape areas) should be monitored on a regular basis during the growing season.

Chemical control

Until recently, little was available in terms of weed-control products that would help eliminate problem perennial grasses from desirable grasses. Two main methods were available, each with serious limitations. In the early days of turf management, hand removal was about the only effective method of eliminating unwanted grasses from turf stands. The process involved using a sod spade or tile spade to pop the crown of the undesired grass plant from the sod. While immediate results were realized, this proved to be inefficient because it was labor intensive and, in many cases, if all of the roots/rhizomes/crown were not removed, regrowth of the undesirable plant would occur, and the need for hand weeding would again rear its ugly head.

In the early 1970s, the glyphosate-based herbicide Roundup came on the market, creating another option for control of grassy weeds. This procedure was also a bit on the crude side, in that Roundup is nonselective and kills most green plants it's applied to. After the undesirable grass began going off-color in response to the application, reseeding of the affected areas with the desired species helped to re-establish the turf stand without the presence of grassy weeds. While this approach was generally considered to be an improvement over hand removal, the downside was that about two to three weeks were required for the process. Meanwhile, golfers were left looking at a dead tee or fairway. Again, not the most desirable of situations.

But recent developments have led to more options for golf course superintendents. Because demand for selective removal of undesirable grassy weeds remained high in the '80s and '90s, many efforts were undertaken to develop products that would kill grasses of a different texture than the common desirable turfgrass species.

Sulfosulfuron is safe on most warm-season grasses, and the cool-season grasses Kentucky bluegrass and creeping bentgrass. It's an excellent yellow nutsedge product, and will also selectively remove rough bluegrass, tall fescue and quackgrass from Kentucky bluegrass. For those wishing to maintain pure stands of Kentucky bluegrass, sulfosulfuron offers selectivity for difficult-to-control perennial grasses. It has also been tested for selective removal of rough bluegrass in creeping bentgrass fairways with acceptable results.

Timing and application technique


John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln.
For grassy weeds, and quackgrass is no exception, the best timing to apply herbicide is when they're first spotted. Postemergence applications are much more effective if the plant doesn't have a chance to develop a root mass and a mature crown. Spot spraying is a wise and judicious herbicide strategy. Strive to scout turf areas routinely, especially if they are known hot spots. Such areas include turnarounds, tee approaches, generally thin turf stands and those with compacted soils.

Whenever possible, try to maximize the amount of surface area on the leaves of grassy weeds. For example, avoid mowing the day before application. If mown three days before, sufficient time will pass to allow regrowth of the target weeds. If the weeds are drought-stressed, timing an application post rain or irrigation often increases success. Some superintendents have realized improved control when the affected area is lightly fertilized prior to herbicide application if the area was not already fertilized.