Ask a turfgrass manager to take a glimpse at the current 7-day forecast, and the last concern they will voice is what to do with their preventive applications for spring dead spot control this fall. While understandable, now is the time to consider how, when, and with what product(s) those preventive apps should be made.
Spring dead spot is not the sole disease of concern going into winter dormancy or prior to covering greens. Take-all root rot, Microdochium patch, and Cream leaf blight all come to mind. However, the most difficult of these pathogens to control are the two that cause spring dead spot.
In the United States, the two species of Ophiosphaerella that cause spring dead spot are O. korrae and O. herpotricha. This may seem to be a purely academic point, but sole active ingredients that provide excellent control of both species are few and far between.
If you’re looking to change up products this year due to undesirable results from past years, your best bet is Kabuto® Fungicide SC. Isofetamid, the active ingredient in Kabuto, is an SDHI fungicide and a top performer of sole active ingredient options for the past four years, particularly when compared to single active treatments such as penthiopyrad and tebuconazole.
Kabuto also provides flexibility that other fungicides labeled for control of spring dead spot do not: it is labeled for use on golf courses, commercial and residential turf, sports turf, and sod farms and has a flexible application schedule. Other SDHI fungicides, such as pydiflumetofen, are only labeled for use on golf courses, while DMI fungicides, such as mefentrifluconazole, cannot be applied to residential turf.
Re-applications may be applied as soon as 14-days post initial application, or out to 28-days (or later) post initial application. Why is this an important distinction? Spring dead spot applications need to go down when soil temperatures at the 2-inch depth drop below 75°F for 3-5 consecutive days in the fall. Sequential applications should hit the ground before soil temperatures fall below 60°F, though recent work by Wendell Hutchens and Dave McCall, Ph.D., of Virginia Tech have shown that applications as low as 55°F are just as effective. A two-application control strategy is preferred, but work at Virginia Tech, North Carolina State University, the University of Missouri, the University of Tennessee, Clemson University, and other locations has demonstrated that a single application of Kabuto at 3.2 fl. oz. per 1,000 sq. ft. provides near complete control of the spring dead spot pathogens.
Is it ideal to rely on one application for control of spring dead spot? I prefer the two-application method, but there is ample data supporting the effectiveness of the one-application strategy with Kabuto. For a two- application strategy, consider applying Kabuto at split rates of 1.0 – 1.6 fl. oz. per 1,000 sq. ft. At most research locations, there has not been a statistically significant difference between those two rates, but the high rate provides >95% control consistently. So, after you choose your rate, make sure the first application going down is when soil temperatures are below 75°F in the fall for three to five consecutive days, make a second application when soil temperatures have dropped to the mid-60’s. That may be two weeks, four weeks, or six weeks; monitoring is key.
Perhaps just as crucial as application timing is immediate post-application irrigation. The product must be watered into the stolons, crowns, rhizomes, and upper rootzone to be effective. The reasoning for this is because of where the pathogen resides and causes infection. At least 1/8” of irrigation immediately after application is essential. I’m often asked, “How much water is too much?” The truth is, you really won’t water a fungicide through the rootzone. Credit on this work goes to Dr. Kerns and Dr. Gannon at North Carolina State University. You really aren’t going to put down too much, so long as water isn’t running off the greens. Effective fungicide applications for spring dead spot are not cheap, so take the time to get the most out of the application by watering it in as soon as the treatment hits the ground.
Although the active ingredient in Kabuto isn’t labeled for use on the other diseases in the late fall/winter/early spring, it is assuredly the most effective product you can include in your fungicide program for control of the spring dead spot pathogens. Not sure which of the two pathogens is causing spring dead spot at your facility or property? That doesn’t matter when using Kabuto. Don’t just take my word for it—ask another turfgrass manager or university researcher who has seen the difference.
- Kabuto: Spring dead spot’s archnemesis – from Chris Lewis at Golfdom