By Mike Jiggens
Up until about 12 years ago, little was known about the control of anthracnose on golf course turf. Since 2002, extensive research on the disease has been conducted at Rutgers University in New Jersey as well as at 11 other institutions, including the University of Guelph.
Dr. Bruce Clarke, director of the Rutgers Center for Turfgrass Science, spoke about best management practices for the purposes of reducing fungicide use while serving as keynote speaker in March at Master’s Turf Supply’s 11th annual seminar series at Milton, Ont.’s Granite Ridge Golf Club.
He said so much more information about anthracnose control has come about in only the past couple of years that it has rendered a previously published book of his already obsolete.
Clarke told an audience of golf superintendents that little tweaks in their management programs can pay big dividends in the improved vigor, quality and performance of their turf as well as helping to reduce their reliance on fungicides.
His presentation was a case study on how such management practices as fertility, mowing, irrigation, cultivating and topdressing can have on helping to reduce such stress-related diseases as anthracnose and dollar spot.
“You should be able to significantly reduce your fungicides either by reducing the rates or extending the intervals between applications,” he said.
It’s the basal rot phase of anthracnose which presents the major problem and not so much the foliar phase. Once it gets into the plant’s vascular tissue, it’s a difficult disease to control. It must be attacked from the root in addition to taking it on through good cultural and management practices.
Before the Rutgers-led study was initiated, it was already known that lowering mowing heights enhanced the disease. The problem, however, is that by raising mowing heights, playability and ball speed are likely to be compromised.
Mowing lower can stress turf, especially during times of heat and drought stress, and that’s when the vast majority of anthracnose problems occur. Clarke said raising the height of cut even slightly can be rewarding in terms of taking the stress off the grass and dramatically reducing the amount of disease.
“You can’t control this disease simply by raising the height of cut, but you can reduce the severity and make it easier for the fungicides to work.”
To maintain ball speed, research has looked at such practices as rolling and increasing the frequency of mowing. A two-year study was conducted to compare single cutting with double cutting for anthracnose severity.
“When we first started this work, everybody thought that anthracnose was a stress-related disease and a wound-related disease, and that’s 50 per cent right.”
Anthracnose is certainly a stress-related disease, Clarke said, noting that anything done to annual bluegrass putting greens to weaken them will enhance the disease. Heat stress, drought stress and low fertility are among the things which will enhance the disease, but it doesn’t need an open window to get in.
“Wounding has very little to do with this disease, and that’s an important discovery.”
Such practices as double cutting, rolling, sand topdressing and dragging it in will wound the plant, but will not increase anthracnose, research shows. Clarke said if a superintendent can manage his turf and perhaps scuff it up a little bit yet not affect anthracnose, there is much he can do to improve the quality of his turf.
Studies show there is no difference in anthracnose severity between single and double cutting.
“Even though you’re double cutting and wounding the plant twice as often, it’s not enhancing the disease. That’s important to know.”
Clarke said many superintendents are reluctant to roll their greens when anthracnose is present. Recent studies, however, show that rolling every other day with either a clip-on unit, a vibratory roller or a sidewinder roller will not enhance anthracnose.
“We’ve never seen an enhancement in anthracnose with rolling. We have, under certain circumstances, seen a slight reduction in anthracnose.”
Why would rolling or smoothing the putting surface actually reduce the incidence of anthracnose? Rolling allows the cut height to be raised while still realizing good ball speed. Because of the increased mowing height, stress on the plant is reduced.
Studies on the effect of rolling on greens affected by anthracnose were done with stimpmeter readings between 9.5 and 10.5.
During periods of heat and drought stress, slightly raising the mowing height and introducing rolling can dramatically reduce the severity of the disease, Clarke said.
“We didn’t know that prior to this work. A lot of people were really afraid to go out there and roll a green if they had a real severe anthracnose problem.”
Good nitrogen fertility is probably the most important practice that can be done for a putting surface in terms of anthracnose, he said. Of all the studies that have been conducted in which various cultural and management practices have been utilized for anthracnose control, nitrogen is “hands down” the most important of the lot.
“You can reduce anthracnose probably 25 to 30 per cent without any fungicides just simply by maintaining a good fertility program, and in particular a good nitrogen program.”
Clarke said when anthracnose is present on greens and tees, increased spoon feeding can pay big dividends in reducing the severity of the disease. He said as much as two-tenths of a pound of nitrogen every two weeks or perhaps each week when the disease is present can allow the plant to recuperate from the infection and significantly reduce its severity.
One must be careful not to apply too much, he warned. Studies show that when amounts higher than one-tenth or two-tenths of a pound are applied every week, there can be a tipping point to where the disease can become worse. It’s possible to add too much nitrogen, he said, but it’s good for most programs.
“Increasing or spoon feeding to a tenth or two-tenths when you have a problem can really help reduce the severity. What we’re trying to do is increase our spoon feeding to try to maximize the benefits of nitrogen in improving plant health and reducing the disease severity because of it.”
A good fertility program can increase the effectiveness of fungicides and reduce waste, Clarke said. Research in which urea, ammonium sulfate and potassium nitrate were studied found the latter was one of the better nitrogen sources for reducing the disease, prompting the question as to whether it was the nitrate or the potassium that was so effective. It was discovered to be the potassium.
All nitrogen sources studied reduced anthracnose, although some were better than others. The most effective, it was discovered, was potassium nitrate. Studies were done to learn why, including a look at pH with the realization that ammonium sulfate lowers pH while nitrates slightly raise the level.
It was concluded that it’s definitely a potassium effect. Soil pH may have an effect, but it’s not really pronounced, Clarke said. Calcium doesn’t seem to have a major effect on the disease at this time. Although various nitrogen forms were studied, none seems to be the effect. After analyzing all of the data, it is the potassium which seems to improve the level of control, he said.
Potassium is known to improve winter hardiness and reduce winter damage. In trials where ammonium sulfate had been applied, there was significant winter damage, but there was little where potassium nitrate had been applied.
In 2012, several potassium sources were studied, including potassium nitrate, potassium carbonate, potassium sulfate and potassium chloride. Each was looked at in 1:1, 2:1 and 4:1 ratios with nitrogen. In the first year of the study, it didn’t matter what the source of potassium was or its ratio, only that potassium was present.
Clarke said the data suggested that potassium was just as important, if not more so, than nitrogen. All of the potassium ratios triggered better results than nitrogen alone or potassium alone.
“So you’re marrying two important nutrients. When you put the two together, you get the least amount of disease.”
The 4:1 ratio is essentially what would be regarded as 1:1 or 1 1/3 pounds of potassium per year applied in small amounts every couple of weeks, or about 16 applications per season. There was no real difference between 1 1/3 pounds and 5 1/3 pounds.
“As long as you were applying sufficient quantities of potassium, the plant had enough and it was reducing disease.”
Clarke stressed that adding potassium won’t eliminate anthracnose, but will help to reduce its severity.
Research is ongoing to study foliar feeds of potassium for getting it into the plant quickly.
Clarke said much has been learned about anthracnose in recent years, including the need to practise sand topdressing. It was previously assumed that adding coarse sand would contribute to wounding of the plant because of sand’s abrasive qualities. In fact, earlier editions of a book he wrote advised against the practice because of the assumption which had never previously been researched.
“It was like adding fuel to the fire,” he said of the earlier belief. “We know that sand topdressing is important agronomically. It modifies the thatch, it smooths the surface, it gives crown protection, and we now know it reduces anthracnose. But we didn’t know that before we started.”
When research into topdressing was initiated, light rather than heavy topdressing was studied. Comparisons were made between one and two cubic feet of sand per 1,000 square feet applied every seven, 14 or 28 days. Another trial in which no sand was used was made for comparison’s sake.
It was understood that no one would ever apply that much sand every seven days.
“You’d need a snow shovel to take it off. But we wanted every possible combination to see what the effect of sand rate and sand interval of application was.”
Results showed most disease was present in plots where no sand was used. The least amount of disease was realized where two feet of sand was applied.
The topdressing study was repeated over a three-year period. It was also done by two other graduate students who repeated it an additional two years. The results were the same every single year. Clarke said this was done to scientifically bust the belief that topdressing would further an anthracnose problem.
“As you increase the amount of sand, you get less anthracnose. It’s completely opposite of what everyone thought they knew. It’s the biggest surprise we’ve ever seen.”
Once believed to be a wound-related disease, anthracnose on a green subjected to sand topdressing would seemingly become worse, but it doesn’t.
Sub-angular sand, in fact, provided better disease suppression than round particles of sand. It provided better stability and firmed up the putting surface. Mowers will sink less into a sanded vs. non-sanded green, allowing for a higher height of cut.
The plants’ crowns will be set deeper and will be less prone to heat and drought stress, making for a more vigorous plant. In a sanded environment, the plants will stand more erect and will be better equipped to capture life-sustaining sunlight.
Clarke said all that’s required is to match turf’s growth throughout the summer with small amounts of topdressing.
“Sand is a good thing. The quicker you can establish a full canopy, the better.”
Adding small amounts of summer topdressing to match the growth of grass is key, he said, adding if it’s growing slowly to add only a small amount of sand, and if it’s growing quickly more sand can be added.
Between 1,000 and 2,000 pounds of sand per year is the target for reducing the disease, Clarke said. He suggested spring topdressing after core aerifying, backfilling the holes and then supplementing light amounts of sand as needed during the summer.
A superintendent who adjusts his fertility and sand topdressing programs can greatly reduce his amount of anthracnose, making it easier for fungicides to be more effective.
Clarke estimated best management practices can reduce fungicide use for anthracnose control by 75 to 80 per cent.
Greens which are maintained too wet will see more anthracnose, he said. The trend is to run greens dry, but, if they become too dry, anthracnose can be enhanced.
Overwatering will result in “lousy” turf, he said. Keeping it constantly wet results in algae and thin turf. Clarke’s take-home message recommended greens be dry, but not too dry.
“You run them too dry, the plants are always wilting and it will predispose the plants to infection.”
He added cultivation practices such as verticutting and light grooming present no real problem with anthracnose.
Plant growth regulators such as Primo began to be widely used on greens about 10 years ago—about the same time that a tremendous increase in basal rot anthracnose became apparent. Clarke said there was suddenly a “guilt by association” with regard to plant growth regulators, but added research clearly shows that not only do PGRs not enhance anthracnose, they can slightly decrease the disease severity when used properly.
Adopting good fertility, irrigation, mowing heights and properly-used plant growth regulators can take about 89 per cent incidence of anthracnose down to about 30 per cent before fungicides are added to the equation, Clarke said.
Although anthracnose is more of a problem with annual bluegrass than with bentgrass, bentgrass can, on continual heat loads, get the disease.
There are currently about 10 chemistries in Canada that will work against anthracnose.
Round table discussion
Following Clarke’s presentation, a round table discussion on foliar nutrition and disease control was conducted.
Tom Weinert, vice-president of turf sales for Plant Food Company, said fungicides should never be eliminated because of the levels at which greens are being cut these days as well as the expectations of club members when they see courses such as Augusta National in all its glory.
What is expected of superintendents today “is kind of silly,” he said, adding things are getting to the point where it’s “stupid.”
“You have to have green speeds from 10 to 14 on a regular basis.”
Some of the people at PGA Tour stops in the United States are “literally nuts,” Weinert said. “They’d rather have dead grass than greens that are rolling 101/2 or 11.”
He said his company deals with both high-end golf courses as well as smaller ones with limited budgets. The latter courses are usually forced to become creative, and Weinert said he gets many of his ideas from low-end clubs and their superintendents because of their limited funding.
Trials of Plant Food products are conducted at Rutgers.
He said one of the clubs he represents in New Jersey has been dealing with a significant mad tiller issue. His company developed a 7-0-7 product, currently in the testing stage, which includes manganese, magnesium and boron, yet is 20 per cent sulfur.
Mad tiller is an epidemic on several golf courses, Weinert said, including Ridgewood Country Club in New Jersey, which is the host site for the PGA Tour’s The Barclay’s later this season. Fairways are cut in the morning, but are beset with mad tiller by the afternoon. When golfers reach the 18th hole, the problem is especially bad. The course superintendent will be using the 7-0-7 formulation to better deal with the issue.
Superintendents who do not engage in best management practices will find that no matter what they put out on their golf course will fail if there isn’t proper oxygen and proper gas exchange in the soil, he said. He said he has known some superintendents who didn’t believe in punching holes in their greens to vent them in the summer. They became sealed off and grass was lost. Those same superintendents have since learned a valuable lesson, he added.
Weinert spoke of the value of flushing greens, adding it’s almost impossible to flush pushup greens. When greens are flushed, there will be a colour response which is actually an oxygen response. A superintendent who previously didn’t believe in punching holes in his greens had also never flushed his greens and encountered some issues in the middle of summer.
Weinert said he talked the superintendent into flushing his greens and basically had to “hold his hand” throughout the process. The procedure included a spray of calcium, some penetrant and some gypsum, and then then irrigation system was turned on and left running for about an hour and a half.
The superintendent had reservations about the practice, fearing he would lose his job because an important tournament was scheduled for the course in a couple of days and he feared the putting surfaces wouldn’t be sufficiently firmed up. Weinert asked him for his trust.
“When you flush, you’re going to run the heads for as long as you possibly can, get puddling and then turn them off, let it go down and do it again and again, until you can run them for 30 or 40 minutes without puddling.”
The superintendent called the following day to say his greens had never been so firm.
After flushing, the system must be “recharged” with a foliar spray, Weinert said.
“Look at your soil report to see what you’re deficient in and then spray with a foliar spray in what you’re deficient in, because you’ve just flushed everything from the system.”