Ridding Rapid Blight

With its natural terrain of lakes and live oaks, and spectacular views of South Carolina's Intracoastal Waterway, Glen Dornoch Golf Club draws an average of 10,000 rounds during the months of March, April and May.

“Spring is our busiest season,” says George Gore, general manager of the 270-acre course that is situated on the northern end of Myrtle Beach's Grand Strand. “That's when all the golfers from up north start heading down here in droves.”

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However, when an unidentified turf disease destroyed the putting greens at this coastal course in the spring of 2000, Gore and his staff stood by helplessly as more than 3,000 of the usual spring rounds disappeared onto other courses in the Myrtle Beach area.

“We gave the golfers the option to play or not,” says Gore. “We didn't want them to play and be unhappy, so we lost a good many of them.”

The disease, named rapid blight because of how quickly it destroys infected turf, devastated the cool-season grass Glen Dornoch uses to overseed its bermudagrass greens.

“It killed the Poa trivialis,” explains Gore of the disease, which cost the course hundreds of thousands of dollars in lost green fees. “It turned the greens into brown circles. The bermudagrass was dormant, so there was no grass for golfers to putt on.”

IDENTIFYING THE PROBLEM

After trying a number of different fungicides, Glen Dornoch was unable to control the disease and asked Clemson University Plant Pathologist Bruce Martin, Ph.D., for a diagnosis.

Martin established a trial of various overseeding grasses to determine which species were susceptible to the fungus. After determining that the host was the Poa trivialis the course uses to overseed roughs in winter, Martin experimented with different fungicides to gauge their activity against the disease.

During his research, Martin also learned that rapid blight was causing problems on golf courses in seven other states, including Arizona, California, Colorado, Florida, Louisiana, Nevada and Texas. In California and Arizona, the disease has caused serious damage to large expanses of Poa annua, Poa trivialis and Lolium perenne (perennial ryegrass).

“All these states have locations with salty irrigation waters,” explains Martin. “That association has been very strong on both the east and west coasts.”

SALT WATER INTRUSION

In the spring of 2001, rapid blight attacked 13 golf courses along the South Carolina coast and one in coastal North Carolina. In each case, Martin discovered, salt water had intruded into the irrigation water. “The disease was being caused by increases of salinity in certain aquifers along coastal environments,” he explained.

Martin observed that the occurrence of rapid blight along the Carolina coast followed a severe drought during which sodium chloride accumulated in the soil. “Because of the drought, salts were building up and not being leached by rainfall,” says Martin. “That made conditions more favorable for the organism, which dwells in salty places.”

In a field trial conducted in the fall of 2000, Martin determined that Compass, Fore and an experimental fungicide were active against rapid blight in Poa trivialis.

“Healing was promoted by Compass (trifloxystrobin) after a single application at 0.2 oz./1,000 sq. ft., and by the experimental fungicide, pyraclostrobin, after a single application at 0.9 oz./1,000 sq. ft.,” says Martin. After two applications at 6 oz./1,000 sq. ft., Fore (mancozeb) demonstrated some curative activity.

In a trial at a coastal golf course in South Carolina, Compass achieved better control of rapid blight when the rate was increased to 0.25 oz./1,000 sq. ft., says Martin.

FINDING A CURE

After seeing the results of Martin's research, Gore directed his crew to apply Compass on the overseeded putting greens during the spring of 2001. They sprayed the material at the rate of 0.25 oz./1,000 sq. ft. on a two-week schedule from March through June. “That took care of it for a while,” reports Gore.

However, when Glen Dornoch overseeded the putting greens with Poa trivialis the following fall, signs of the rapid blight fungus became evident about two weeks after germination. To prevent the disease from taking hold on the putting greens, Gore directed his staff to spray Compass on a two-week schedule for the next eight months, if necessary.

“We have a handle on rapid blight now,” says Gore. “We know what it looks like and we can cut it off.”

Barbara McCabe is a freelance writer who lives in Philadelphia, Pa.

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