2014 weed round up

Humorist Dave Barry once said that crabgrass has the uncanny ability to grow on a bowling ball in an airless room with no way to kill it other than nuclear weapons. It’s a funny assessment, and it might be true, but it’s no laughing matter for turf professionals.

While romantics may simply view weeds as plants with a desire to grow, superintendents see them as Public Enemy No. 1. Luckily, the experts are here with their predictions on this season’s weed pressure.
 

Southwest

Bowling balls aside, crabgrass is the real problem in the Southwest, says Kai Umeda, turfgrass extension agent for the University of Arizona. In the low-desert region, crabgrass and southwest cupgrass begin appearing between March and May. Nutsedge will start appearing as early as February in warmer, more exposed areas.

“It takes close inspection to confirm what you are dealing with,” says Umeda.

“Crabgrass and cupgrass look very similar, but cupgrass does not have any visible hairs on the stem or leaves. The seedheads are also distinctly different, but it is too late to control when they appear. Use a hand lens to observe the hairiness around the collar region of the leaf and stem,” he says. For identification, Umenda recommends using ‘Weeds of the West,’ a publication from scientists at the Western Society of Weed Science.
 

Mid-Atlantic

Poa annua and, to a lesser extent, clover continue to be challenging spring weeds in the Mid-Atlantic, says Elliott L. Dowling, agronomist with the region’s Green Section.

“For most superintendents, these two weeds in particular are the easiest to identify. Poa can be challenging if seed heads are not present, which they typically are in the spring unless preventative applications were made. If in doubt, consult a colleague or ask any Green Section agronomist. They will be happy to help,” he says.

“Additionally, weed identification apps are a valuable tool for any turf manager. I recommend downloading one on your phone. They are quick and easy to use. If you’re still unsure, reach out for help.”

Darin S. Bevard, director of the Mid-Atlantic Green Section, also stresses the importance of proper identification and diagnosis.

“The first thing to do is to ask another superintendent for help if you need immediate input.” Bevard says. “With modern technology, it is very common for a superintendent or assistant superintendent to send me a picture via text or e-mail. Sometimes I will be on a visit and someone will show me a weed and ask me what it is. It is critical to properly identify weeds so that the best course of action can be selected for control.”

Once identified, the best method to treat the weeds depends on the turf surface, says Bevard.

“The first thing that should be done is to make sure that whatever herbicide you select for control will not injure any desirable grasses or at least be certain that the extent of injury can be tolerated for a period of time.”
 

Mid-Continent

Charles “Bud” White, director of the Mid-Continent Green Section, sees crabgrass, nutsedge kyllinga, and goosegrass as the major weeds in his region.

Fortunately for superintendents, they are fairly easy to identify.

If you’re looking for a little extra help, White suggests the University of Tennessee extension website, which is “especially good with identification info.”
 

Southeast

Lambert McCarty, professor of agricultural, forest and environmental sciences at Clemson University, has a list of winter annuals that will rear their ugly heads in the spring. Included on the list are annual bluegrass, henbit, hairy bittercress, annual blueeyedgrass, wild onion/garlic, henbit/purple deadnettle and Carolina geranium. Summer annuals such as crabgrass and goosegrass also present problems for\ superintendents in the region.

For identification, McCarty recommends using the ‘Color Atlas of Turfgrass Weeds.’
 

Florida

In Florida, USGA Green Section senior agronomist Todd Lowe sees goosegrass on his radar.

“It’s a perennial problem on most Florida golf courses, but there are a variety of herbicides to manage it,” he says. “Tropical signalgrass has emerged as one of the most difficult weeds to control, due to the loss of MSMA.”

Having dealt with goosegrass before, most superintendents have no trouble with identification. But, he adds, “tropical signalgrass is a little more difficult to identify because it looks similar to crabgrass. It forms thick mats, unlike most crabgrass, but the distinctive difference between tropical signalgrass and crabgrass is in their seedhead morphology.”

Lowe suggests to look carefully for those seedheads: “Crabgrass seedheads somewhat resemble a hand, whereas signalgrass seedheads hang off the main stem at a 90-degree angle, like a signal flag.”

Growing a healthy stand of turfgrass is one way to avoid weeds, but you may also want to stop overseeding in the winter.

“Overseeding with perennial ryegrass creates thin and bare areas in spring,” Lowe says. “These bare areas are then colonized by other plants and weeds as the Bermudagrass recovers.”
 

Northeast

James Skorulski, senior agronomist in the Northeast Green Section, says annual grasses receive the most attention in the region and are usually targeted with preemergent products.

“Crabgrass populations seem to be spreading to northern parts of New England and Canada,” Skorulski says. “Goosegrass is becoming more prevalent in recent years with the warm summers. It seems to be working its way further north and remains most common along cart path edges and other areas of compaction. It’s also becoming evident in some practice tees and other areas.

“There are the regular broadleaf weeds such as dandelion, plantain, prostate knotweed, and clover,” he adds. “The other weeds that are becoming more prevalent, especially in coastal and southern parts of New England, are green and false green kyllinga and bull paspalum.”

Aside from paspalum, which can be confused with crabgrass, these weeds are fairly easy to identify, says Skorulski. Paspalum – usually found in dryer areas like roughs and bunker banks – is a perennial unaffected by preemergent herbicides. Kyllinga may be confused with nutsedge, but it’s much more aggressive and tends to form mats.
 

Northwest

The Northwest Green Section, headed by director Larry Gilhuly, sharply contrasts with the abundance of weed varieties in the Northeast. In the Pacific Northwest, Gilhuly sees clover, dandelion, and other broadleaf weeds. In Hawaii, it’s all goosegrass, smooth crabgrass, and torpedograss, which are problematic year-round. In all these cases, he says, the weeds are fairly easy to identify and diagnose.
 

North-Central

The worst weed offenders in this region are dandelion and clover, says Robert C. Vavrek, Jr., senior agronomist in North-Central Green Section. Luckily, both are easyily identified.

“There are good weed identification keys on a number of university turf management websites,” he says.
 

Treatment

Once dandelions are identified, Vavrek says, most superintendents will treat them curatively. Some treat crabgrass preventively, while others wait to control crabgrass with herbicide after it germinates.

Of course, an ounce of prevention is worth a pound of cure.

“Fall treatments for perennial weeds will lessen weed pressure during spring,” says Vavrek, acknowledging the difficulty superintendents often face in getting on the course early in the season. “Many treat for dandelions too early. The weeds are not growing rapidly enough to absorb a lethal dose of herbicide. The weeds are stunted for a while, but they will recover.”

Dowling also finds preventative measures to be the most effective, pointing out that it is difficult to maintain control if you try to apply products curatively.

“Eliminate and control as many weed species as possible before they become a problem on your golf course,” he says. “The best method to control spring weeds is kill them in the fall. The more you can do in the fall, the less the spring outbreaks may be. Additionally, focus on the health of desirable plants. Providing complete coverage will reduce the likelihood of weed species germinating. Use desirable turf to out-compete weeds.”

Preventative control boils down to knowing what your weed problems are in advance, says Bevard.

“Summer annual grasses (crabgrass, goosegrass, etc.) should be controlled with a preemergent herbicide with an early spring timing if pressure from these weeds is high,” he says. “If there is low pressure from crabgrass and goosegrass, some superintendents opt for spot treatments with post emergence heribicides.

“If you have broadleaf weeds such as clover and dandelion, herbicide applications can be made in the fall to eliminate most of the problems,” he adds. “Then you do not have to deal with the problem in the spring, or at least the problem is far better than it would be otherwise.”

Still, according to McCarty, many curative options do exist.

“Winter annual weeds are easier to control with postemergence herbicides in our region because Bermudagrass is often not actively growing when these weeds are present,” he says. “In contrast, crabgrass and goosegrass are more difficult to control because of the lack of selectivity of postemergence herbicides which control these weeds. Of course, if the facility is overseeded, this complicates the situation considerably.”

Lowe balked at the idea of completely ridding a course of weeds. “Terms like ‘elimination’ and ‘eradication’ should not be considered. There’s only ‘weed management.’ The soil seedbank on most golf courses is very high, and many weed seeds can lie dormant for decades. If given the right opportunity, seeds can germinate and establish quickly in a subtropical environment,” he says.

“Weed management begins with strong, dense turf. The best defense is a good offense.”

Rob Thomas is a Cleveland-based writer and frequent GCI contributor.