Resistance is not futile

Fungicide resistance is on almost every superintendent’s mind. Recent research of 279 superintendents conducted by GCI in partnership with AMVAC Chemical Corp., found 74 percent of respondents were most concerned with dollar spot resistance issues and 19 percent report the same trepidation when battling anthracnose resistance.

Superintendents are considering new modes of action essential in fungicide resistance management, says Dr. Charles Silcox, AMVAC product development manager. “This clearly shows that the topic of resistance has the attention of superintendents,” he says. “In terms of resistance by dollar spot and anthracnose, the situation is worse now than it was five or 10 years ago, or longer. We have had some fungicides with new modes of action come into the turf market, but we have also lost some options due to resistance development.”

Part of the reason is dollar spot and anthracnose are active for relatively long periods of time and are exposed to many fungicide applications during the course of the year, Silcox says. This places pressure on the populations to develop resistance. Many other diseases do not receive this amount of selection pressure, so the time for them to develop resistance is longer.

In the Midwest, these two diseases are the most sprayed for diseases that the golf industry strives to manage, says Todd Hicks, program coordinator of The Ohio State University’s Turfgrass Pathology Program, Department of Plant Pathology. With more applications being made, there is more chance for resistance issues to develop.

Paul Culclasure, superintendent at Kilmarlic Golf Club in North Carolina, has seen resistance issues in the past to mancozeb and a DMI (demethylation inhibitors) fungicide that had been heavily used in the past. This was coupled with some overlooked fertility issues and water mismanagement.

“At the same facility we found some anthracnose on the ‘50/50’ Penncross/Poa greens. There were occurrences on both species and I also had trouble getting control with a strobilurin that is typically very effective on this particular disease,” Culclasure says. “Dollar spot has been demonstrating resistance issues for many years now, though with the introduction of new fungicides as well as awareness to the issue, I feel the industry has done a better job of control.”

Culclasure adds anthracnose “is just now becoming a player in my area,” and resistance issues will be a “hot topic” for this disease in the very near future.

Resistance issues can be regional in nature, and weather in certain regions will often dictate how many fungicides are applied targeting a certain disease, says Dr. Paul Koch, assistant professor in the Department of Plant Pathology of the Molecular and Environmental Toxicology Center of the University of Wisconsin-Madison.

“For instance in the Midwest, nearly every fungicide that goes out in the summer has at least one component that targets dollar spot, which means there are lots of opportunities for the fungus to develop resistance,” Koch says.

In other areas of the country, it actually gets too hot for dollar spot in the middle of the summer, and more applications are targeting pythium and brown patch as opposed to dollar spot. In the Northeast, the continuous heat and humidity make for much more aggressive anthracnose that could develop resistance, while the lower humidity in the Midwest has led to fungicide-resistant anthracnose being less of a problem.

Midwest weather is an issue when trying to prevent or treat the pathogens during the summer, says Frank Sutter, superintendent at Indian Springs Golf Club in Illinois. “The hotter or more humid it is cuts your control time,” he says. “I normally spray on a preventive basis. I feel if nighttime temperatures stay above 75 degrees that I have lost two days of control for every 24 hours.”

Resistance issues with dollar spot in the Pacific West Coast of Canada are relatively new, says Josh Webb, assistant superintendent at Quilchena Golf and Country Club in Richmond, British Columbia, Canada.

“Originally being from Ontario and moving to Vancouver over six years ago, dollar spot was always something we were dealing with, as we saw resistance to propiconazole,” he says. “Once I was out West, colleagues claimed they had never seen dollar spot so severe until the year I arrived in 2009. We have been battling it ever since.” His plant health program provides “excellent” control of dollar spot through the use of phosphites and constant rolling.

“However, where we do not roll on a regular basis (tees and fairways) the dollar spot is much more prevalent and hard to control. In 2010, we lost nearly 75 percent of our north/south running fairways to dollar spot because of shade issues from trees,” Webb adds. “Since then, we have increased our use of phosphites and wetting agents and have seen a significant and compounded decrease in dollar spot each year. We have not used any fungicides to combat dollar spot on tees or fairways, only Daconil (chlorothalonil) on greens and approaches on a preventative basis.”
 

Anthracnose control on Quilchena Golf and Country Club is also on a preventative basis, however, Webb stresses, not with the use of fungicides. “Some of our greens were affected pretty severely this year,” he says. “We started with a new phopshite product at the beginning of last season and the response on greens for suppression of diseases was remarkable. Research has shown that the use of phosphites in a sound routine plant health program should preventatively protect the plant, however, this year was not the case.”

One of the biggest mistakes turf managers make is not making sure they rotate chemical families, Hicks says. Just because a product has a different name and active ingredient, doesn’t mean you are using a different chemical family.

Koch concurs. “I think the most common mistake is rotating amongst products but not rotating amongst chemical classes,” he says. “While there are several differences between propiconazole and other DMIs like triticonazole, from a resistance standpoint the fungus basically sees them as the same thing.” Superintendents should develop an agronomic plan that will minimize the likelihood of disease development, Silcox says. “Researchers at Rutgers University have developed an excellent working outline of best management practices for anthracnose,” he says. “Similar information is available for dollar spot. A sound agronomic program will allow fungicides to perform better and will also reduce the pressure for resistance.” Also, he advises superintendents to incorporate as many fungicide modes of action as possible into an annual control program. Include both contact and systemic fungicides and use a mixture of active ingredients with modes that have been proven effective against the target disease.

David Beanblossom, superintendent at Chariot Run Golf Course in Indiana, has battled dollar spot at the 15-year-old course. “In 2013, we had resistance issues with a number of different fungicides we sprayed. I have since changed my fungicide rotation and the last two years we have been very clean,” Beanblossom says. “We have rotated of fungicides and used some of the new chemistries that are now on the market. Without sounding like I am doing a commercial for Syngenta, my spray program is centered around Daconil, Secure, Velista and Briskway.”

Culclasure also rotates fungicide classes and/or modes of actions; tank mixes when possible (“I like to use a contact and a systemic together when I can,” he says), and checks nitrogen levels, cation levels, and pH in his soil, which he believes can all play a factor in disease management.

Superintendents should use the right product at the right time for the right issue, the right volume and right placement, Hicks says. “Remember, if there is a case of anthracnose-basal rot, the fungicide must be placed at the base of the plant to be most effective,” he says. “Most systemic fungicides only move upward. Secondly, make sure your spraying is working the way you think it is. Check the nozzles, pressure and application volume.”

With the economy and industry the way it is, all superintendents have to do more with less. Therefore, Webb believes trying new methods of controlling diseases, while staying within the constraints of tightening budgets year after year is causing “a lot of the problems.” He adds, “If you have the budget to preventatively control dollar spot and/or anthracnose, then you’re doing well. However, sound cultural practices play a huge part in controlling any diseases, and this is what most superintendents have been forced to collaborate, along with curative applications, to control diseases.”

Webb says if superintendents are using fungicides to preventatively control dollar spot and/or anthracnose, avoiding sequential applications of the same chemical family is prudent. Rotating fungicides reduces the risk of disease resistance of certain chemicals, which in turn will not limit your ability to spray chemicals that may have gained some resistance from overuse.

Developing a fungicide program can be perplexing because it must take into account multiple pathogens over the course of a long season, from early spring to late fall. Silcox says the sheer number of standalone and pre-mixed fungicide products in the turf market can make it very difficult to devise a sound program to control a disease that may be present for an extended period of time.

He talks about an experience he had with anthracnose this year. A superintendent in Ohio wanted to start his anthracnose program with a tank-mix of Autilus and Mirage.

“This treatment got him off to a great start and then he went into his normal rotation. He called me in early August saying that he was having anthracnose show up in certain areas,” Silcox says. “His last application went on about two weeks prior to our conversation and when he told me what he had applied, I had never heard of the product. I asked what it was and he told me it was a premix of active ingredients X and Y. Well, active ingredient X is no longer effective against anthracnose due to resistance, and active ingredient Y never had anthracnose activity to begin with, thus he created an ideal gap in his program that anthracnose could exploit under conducive conditions. To get him back on track, I suggested three products for him to consider and recommended that he tank-mix two of the three and make an application as soon as possible.” The approach worked.

Silcox says, “It is always exciting to find new modes of action on key turf diseases, but it is becoming more and more difficult to identify new modes of action and bring them to market.” Two new modes of action for anthracnose control were introduced this year, penthiopyrad (Velista) and PCNB (Autilus), which have shown excellent activity and may be introduced into an anthracnose management program. Autilus is best used early and late in the season. Velista also is very good controlling brown patch activity, which makes it a good choice during the heat of the summer.

Being aware of resistance issues on your course, taking steps to rotate product to avoid pathogen resistance and, perhaps most important of all, taking steps to prevent the conditions where dollar spot and anthracnose may occur are all vital factors in keeping your turf healthy and disease-free.

John Torsiello is a Torrington, Conn.-based writer and frequent GCI contributor.