By Mike Jiggens
Dealing with dollar spot is almost as commonplace as mowing greens, tees and fairways. For golf course superintendents, it’s like co-existing with a pesky housefly which might move on for a while, yet always returns to be an ongoing nuisance.
Scores of golf course superintendents visited Grand Niagara Golf Club and the Sarnia Golf & Curling Club in late August to listen to Penn State University plant pathologist Dr. John Kaminski speak about dollar spot and other turfgrass challenges during back-to-back course tours, sponsored by Syngenta Canada Inc., the Western Ontario Golf Superintendents Association and the Kent-Essex Golf Superintendents Association.
Kaminski said dollar spot is evolving into more and more of a problem, and extensive research has been ongoing since 2005 to better look into the disease from several perspectives, from resistance to its association with changing nozzles, water volumes, plant growth regulators and mowing frequencies.
Superintendents have told Kaminski their treatments for dollar spot have often been breaking down after about 10 days. When his research first began, studies were done using two gallons of carrier per 1,000 square feet which he said is a particularly high water volume for controlling dollar spot on fairways. The research led to a study of application nozzles that would improve the dispersal of product at a water volume which superintendents would more logically adopt for fairway use, namely one gallon per 1,000 square feet.
When putting the products down, research looked at contact vs. acropetal penetrants, as well as localized systemics, studying the influence of various nozzles. TurfJet nozzles, which put out a coarse droplet size, were typically shipped standard with sprayers in the United States and were consequently used most often, Kaminski said.
The efficacy of the fungicide sprayed, however, wasn’t particular effective, and TurfJet officials met with representatives of Syngenta and a number of scientists to come up with answers. It was learned that TurfJet nozzles were supplied for their ideal low-drift attributes, but the coarse droplet size of the product delivered wasn’t effective in dollar spot control for fairways.
Kaminski said the TurfJet nozzles will work, but only seven to 10-day control will be realized. Opting instead for air injection or turbo TurfJet nozzles will provide 14 to 21-day control.
“Now we can tell people, you can spray at a gallon, but don’t use the TurfJet nozzles. You can get better control out of it at the low volume you need.”
Dollar spot is more intensely managed on putting greens and doesn’t present the same degree of problem it does on fairways. Higher water volumes can be used on greens.
“If you can get away with two gallons on your fairways, those TurfJet nozzles will work fine. You won’t even notice the difference, but when you start dropping that water volume, then you have to switch it up.”
Approximately 1,300 isolates were collected from about 200 golf courses throughout the New England for study, and it was found that resistance was a bigger issue than was originally anticipated, Kaminski said.
Eighteen of the 21 most intensely managed courses sampled had significantly reduced efficacy from the demethylation inhibiting (DMI) fungicides used. He said if there is reduced sensitivity, a fungicide's efficacy will also be reduced. With those DMIs, he said, where 14 to 21 days were once the norm, now it had become 12 to 14 days, meaning that either rates would have to be increased or intervals shortened, “but they still work.”
Sarnia superintendent Paul Brown said he mows all 18 of his fairways daily from Monday to Friday and then cuts nine on Saturday and the remaining nine on Sunday. The frequency also helps to remove dew and reduces the volume of clippings for each mow.
Not all golf courses can afford the cost of labour associated with such frequent mowing, Kaminski acknowledged, or to utilize two individuals to whip dew from their fairways using golf carts. But doing so can make a “huge, huge” difference in total disease severity.
“The key is to keep removing dew as early as possible.”
Kaminski said he has been told by a number of superintendents that they will experience higher levels of dollar spot on one particular fairway than the others. He will ask those individuals about their mowing patterns in terms of cutting sequence. Almost always, he said, the last fairway to be mowed is the most problematic. He suggested superintendents experiencing such problems—if they are unable to regularly drag their fairways—should switch up their mowing patterns in a reverse order and alternate the pattern every few weeks.
Research conducted by Dr. Thomas Nikolai of Michigan State University has found that dollar spot incidence on greens is reduced when their surfaces are regularly rolled. Soil moisture within the top inch or so is generally increased two to three per cent. The increased moisture retention might pose a challenge for pythium and brown patch, but the opposite is true with dollar spot, Kaminski said. The disease fares worse in drier soils.
With dollar spot, dew and leaf wetness are key contributors, but it’s not the same as moist soil, he said. Research shows that when soils are drier, dollar spot is more of a problem.
“Usually when your soils are real dry and then you get a rain storm, it supplies enough moisture for it to blow up overnight.”
But, according to studies, with that much of an increase in soil moisture, a reduction in dollar spot was realized.
At the 2013 U.S. Open, played in June at the East Course at Merion Golf Club in Ardmore, Pa., large rollers were used to push water from the fairways which had been rolled seven days a week. Realizing the amount of labour involved, the club’s superintendent began mowing fairways three to four times a week and rolling on the other days while still maintaining quality, “and the level of his dollar spot plummeted,” Kaminski said.
Merion’s superintendent discovered that the amount of labour he saved would soon pay for the rollers.
Kaminski said this “crazy” idea of rolling fairways was not only thrifty, but helped reduce the incidence of dollar spot.
Early season dollar spot application is typically done once turfgrass is actively growing in April, usually about the time of the second true mowing. Kaminski admitted little is still known about the biology of dollar spot and how it moves about, but it’s a well-known fact that it shows up in late May. If one sprayed in mid-April in one area but left another area alone, dollar spot would appear normally about May 28 but likely wouldn’t show in the other location until a couple of weeks later.
“When it does start showing up in the areas you treated early, they are really tiny infection centres…little flecks that you can easily see and get a jump start on. When you spray in a curative fashion on those, you handle it so much better than when you get the big dollar spot that comes out overnight.”
Kaminski said he doesn’t recommend early season treatment for anyone unless they have chronic problems with dollar spot.
“If you don’t and you’re managing it as it is and it’s fine, that’s just going to result in an extra fungicide application. It’s not really going to save you an application. You think it might, but it really doesn’t.”
He said if in mid-April that dollar spot isn’t readily apparent for 65 to 70 days, when it does come in it isn’t as aggressive.
“If you let dollar spot get out of control or even start getting ahead of you, your rates are higher, your intervals are shorter, and you end up with a lot more pesticide over the course of a year.”
For those who experience chronic dollar spot problems, Kaminski suggested early season application, tank mixing and rotation, dew removal, rolling on at least greens, and continuous spoon feeding of nitrogen.
Once the golf season has reached the latter stages of August, superintendents are typically becoming tired and their budgets are all but exhausted. The inclination is often to stretch treatment from 14-day intervals to upwards of 21 days, “and then when it hits, it hits you fast and hard and is difficult to get under control,” Kaminski said.
In his research plots, one is given no treatment at all during the course of a season while another is treated regularly every 14 days. By late August, the untreated plot gets 70 to 80 per cent disease, but recovers naturally without assistance, improving to about 20 to 30 per cent within a month. At the same time, when applications are ceased or stretched in the normally treated plot, dollar spot incidence skyrockets, shooting up to 80 or 90 per cent in two to three weeks.
Kaminski said it seems counter-intuitive for that to happen because the untreated plot recovers whereas the the plot under year-long control experiences a surge in dollar spot.
What happens, he said, is that when the pest is being controlled all season long on a regular timetable, but that window is stretched to 21 days or longer when it shouldn’t be, the disease takes off.
“Controlling it at that point is damn near impossible. I really believe that this isn’t a function of some new disease. It’s a function of once you let it get out of control in the fall by stretching the windows, you get caught and it’s very difficult to get under control.”
Kaminski said he tries to warn superintendents that if they get tired late in the season and their budgets are gone, that stretching windows will result in dollar spot taking off, “and when it does, you’re screwed.”
Dollar spot can be best controlled when the urge to stretch fall intervals is resisted while adhering to basic agronomic practices during the season, including dew removal, proper fertility, and practising good tank mixing and rotation.