Superintendents who thought their turf was safe from summer patch last year were surprised when the heat gave the pathogen a chance to show up stronger than ever. Dr. Bruce Clarke, director of the Rutgers Center for Turfgrass Science, shows how to best protect your turf this year, and, even if summer patch burns in, how to stop it in its tracks.
What makes summer patch show up so strongly during hot seasons?
Last year, in New Jersey and in many states, it was the hottest summer on record. We had significant breakthroughs of summer spot because of the heat stress. Summer patch is very strongly affected by the temperature, and during heat stress you see a lot more of it. When you have a year like last year, you see which programs worked, and which programs needed to be fine-tuned a little.
What are some ways a superintendent can protect his turf from summer patch?
First, superintendents should check their cultural practices to see if they match up with current best management practices for anthracnose on annual bluegrass putting greens. For example, if you’re below 1/8 inch mowing, we suggest you raise the cutting height and then roll the turf or double cut to maintain acceptable green speed. Make sure the soil pH is not too high. Take soil samples from the top 1.5, 2 inches of turf. Try to maintain a soil pH of around 6.0. The disease is much worse at a high pH, greater than 6.5.
Superintendents can reduce the disease by managing cultural practices. If it’s showing up, I’d say to reassess their cultural management and fungicide program. They can use an ammonium nitrate or sulfur-coated urea fertilizer to help manage the pH level. The former has a high potential for burning the turf; so it should be used in cool weather or applied in small amounts during hot weather. Check the pH level of the soil periodically to make sure it is maintained as close to 6.0 as possible. Reducing the stress on the grass during the high temperature is very important. Many supers who have had a history without summer patch were lulled into a false sense of confidence in their programs. The summer of 2009 was relatively cool, and the disease was not very severe, but in 2010, we had record heat and many programs just weren’t as effective.
What kind of fungicide program should supers use to combat summer patch?
Are they using the proper chemicals to control summer patch? These include the DMI fungicides, (e.g., Banner, Bayleton, Tourney, Triton, Trinity, Eagle, etc), as well as the QOI fungicides (such as Heritage, Insignia and Disarm). You want to make sure you’re using the right fungicide at the right intervals and proper rates. These products should be applied every two to four weeks for optimum control. At low rates, they should be applied every two weeks. At a higher rate, they are usually effective when sprayed every four weeks.
Transition to or resodding with bentgrass is always an option, but that can be expensive and annual bluegrass often just comes back into the affected area over several years. Sometimes there are underlying problems with the location such as a lot of shade or poorly-constructed greens. If that’s the case and you don’t take care of the problem, you’re just going to go right back to annual bluegrass and eventually summer patch. For best results, check your mowing height, make sure it’s not below 1/8 inch, avoid using products that contain high levels of nitrates since this nitrogen source can raise pH and intensify disease severity.
How often should fungicide applications be made?
We recommend the first application of a fungicide when soil temperatures at about a two-inch depth reach or exceed 65 degrees for about a week. Check the temperature of the soil during the middle of the day, between about 12 to 2 p.m. When the maximum soil temperature reaches or exceeds 65 degrees for about five to seven days, it’s time to start your summer patch fungicide program.
You’re really looking at about three summer patch fungicide applications during the summer: one at the end of May, one at the end of June and one at the end of July. The only time there would be another application, at the end of August, would be if it’s exceptionally hot at the end of August, with a forecast for continued hot weather through most of September.
Isn’t that difficult for superintendents on a tight budget?
In order to make the best use of the fungicide program, it’s important to look at the total disease picture and use a fungicide when you can control more than one disease at a time. For example, we often recommend the first application is a DMI fungicide since it will control dollar spot and anthracnose as well as suppress summer patch. Use QOI fungicides for the second and third applications for the control of brown patch and Pythium as well as anthracnose and summer patch. To save money, think about it more globally. You don’t want to waste an application.
If superintendents do see some breakthrough for summer patch, what should they do?
If summer patch appears, apply 0.2 pounds of ammonium sulfate to the affected area and immediately water it into the thatch. It can burn turf, but shouldn’t at that low amount if it’s immediately watered in. That acidifies the root zone in the top 1/2 to 1 inch of the soil profile. Follow that with thiophanate-methyl. It’s not effective on a preventative basis as the QOIs or DMIs, but it works pretty well on a curative basis to prevent the symptoms of summer patch from getting more severe. Using that approach, we tend to arrest symptoms for two to three weeks. It’s a kind of stop-gap until the cooler weather develops in the fall and the grass recovers. A super might do that and still say, “Well, it’s not looking any better.” It’s not any better because the root systems are extensively damaged by the time you can see patch above ground, but this can hopefully keep it from getting any worse. You can’t expect miracles overnight in the heat of summer, so recovery may take several weeks to become apparent.
The best way to confirm summer patch is to express a sample to a diagnostic lab. Take a sample about the size of a cup cutter that is 4 or 5 inches deep from the edge of patches that have recently appeared, and send it to a reputable diagnostic lab to obtain a definitive diagnosis.