Golfdom • June 2022 • Here to stay

Modern fungicides are formulated to stay in the top two inches of the root zone, but timing and irrigation are vital

When looking to stamp out root zone pathogens like spring dead spot, some turf professionals worry about overwatering after applying a fungicide.

These products come at a price. What’s the point of buying a premium product only to misapply it? It’s like watching your friend ask for a bottle of ketchup after the $90 steak is set in front of him.

Industry experts say in the case of overwatering a fungicide application, the fear of drowning out the product is unfounded. That’s because companies formulate modern products like Kabuto^® Fungicide SC to avoid sinking too low into the soil and past the area meant for treatment.

“This is something we worked on for many years,” says Jim Kerns, Ph.D., professor and Extension specialist, North Carolina State University, department of entomology and plant pathology. “With fungicides, only a very small group of them move down into the plant. Every other fungicide stays on the leaf or root surface or moves laterally across the leaf or root. Sometimes, they’re translocated upwards. So, what we started focusing on is that with a lot of root diseases from spring dead spot, Pythium root rot, they’re all affecting the roots, so the question became, ‘How do we get the fungicide to where it needs to be?’”

According to Kerns, spring dead spot symptoms appear in circular patches from six inches to several feet in diameter that remain dormant as turf greens up in the spring. These patches eventually die and collapse on the soil surface. Affected areas recur in the same spot each year and increase in size by up to several inches each season.

Intensely managed bermudagrass, such as golf courses and athletic fields, are prime spots for spring dead spot to manifest. Unlike take-all patch, spring dead spot does not decline in severity as the turf matures and becomes more severe if left unmanaged.

The spring dead spot fungus attacks the roots, rhizomes and stolons of bermudagrass during the fall and winter. This activity does not directly kill the plant but instead makes the bermudagrass more susceptible to freezing injury. As a result, spring dead spot is most severe in the northern range and is usually more severe after extremely cold winters, according to research conducted by Kerns and colleagues.

Modern fungicides like Kabuto have come to the forefront to combat this nemesis of superintendents. University research continues to monitor the effectiveness of these fungicides and the nuances of properly applying them.

Kerns says two general keys to success when applying Kabuto are to not worry about the amount of irrigation but do be sure to be timely with the water.

“To put it simply, it’s very, very hard to overwater with something like Kabuto and root zone pathogens,” he says. “But you need to get that irrigation done as soon as possible to make sure the (fungicide) is getting deep enough into the ground.”

Brian Aynardi, Ph.D., Northeast research scientist at PBI-Gordon, agrees with Kerns. He adds that feedback from Kabuto users in their battles against spring dead spot remains glowing.

“I like to say that the only time Kabuto doesn’t work great on spring dead spot is when you don’t water it in,” he says. “Essentially, that’s where you need to get the fungicide. What I tend to tell people is, ‘You’re spending a decent amount of money on your fungicide. We’re not talking $30 per acre applications here.’ If you’re going to spend to get something of high quality, like Kabuto, you need to water immediately. If it’s important enough for you to go the extra mile for a better product, just water it right away.”

Aynardi urges users to begin their post-application irrigation as soon as possible. He recommends irrigation within six hours of putting the fungicide down to avoid the product bonding to organic matter or being absorbed by plants at the surface level.

“You’re not going to water Segway or Kabuto through the root zone,” he says. “You’re just not. It’s almost better to put more water down with those products because the product isn’t going past the root zone. Most of it is going to stay within that top inch to two inches, and it’s not going to go past four inches.

“With turf, I can think of one or two fungicides, not from (PBI-Gordon) that might get watered below the 4-inch mark,” Aynardi continues. “It will vary a bit depending on organic matter that’s present and maybe if it’s soil that’s sand-based or more of a heavier soil with clay. Even then, there’s so much organic matter with turf that Kabuto isn’t going to move too far down.”

Kerns says he saw a course with a “solid” fungicide program that struggled with diseases in certain areas. Implementing adjustments in irrigation patterns immediately helped the course see better results.

“I looked at their prog ram and thought, ‘There shouldn’t be a disease,’” he says. “But none of those materials were being watered in. Things turned around immediately after that adjustment.”

Kerns says recent research, along with the phasing out of older products, makes the overwatering concern a thing of the past.

“Some older products were more mobile in the soil. That’s part of the reason they were removed from the marketplace,” he says. “With research from four or five years ago, we were worried about resistance in the pathogens starting to develop. It turned out that, basically, we had to increase the water to make sure the (fungicide) was getting where it needed to be.”

A product’s organic carbon partition coefficient rating (Koc) is one of the better ways to anticipate its ability to travel through soil or stay at a desired depth, says Aynardi.

He points to Kabuto’s rating of 489 as an ideal measurement to ensure it gets to the necessary depths while also not going too low.

“You don’t want too low of a value,” Aynardi says. “It’s also a lot more complex than just that number. For comparison, you might find an insecticide with a value of 5. They’re very water-soluble and they can move further down. What we’re finding with fungicides is you can’t water them through the root zone except in cases where something has an extremely low Koc value. You also need other factors in place for that to happen like the light soil with sand, the weather, a lot of things in the world coming together to create that result.

“I don’t want people to think they can’t water things through a root zone,” Aynardi continues. “You can. However, with Segway and Kabuto, you’re just not going to put down too much water to where it goes down too far. To even possibly do that, you’d have to be putting down something like a couple of inches of water, running the water for 24 hours straight. From a 1/8-inch to 1/4-inch irrigation post-application, you’re not going to overwater.”

For comparison, Aynardi cited other products with Koc ratings as high as 16,000, making them essentially immobile in soil.

“With anyone who’s used Kabuto, I have yet to hear anything other than people being extremely satisfied with the outcomes they’re seeing,” he says. “People who use it love it. People who haven’t tried it and still have spring dead spot, I think, are missing the boat.”