Preventing and controlling spring dead spot disease can be one of the biggest challenges for golf course superintendents in the transition zone. Recent research on this unpredictable disease causing random brown patches that appear in the springtime has led to new recommendations to help prevent and control it.
Turf researchers Dr. Bruce Martin of Clemson University and Dr. Lane Tredway of North Carolina State have compiled a list of the top “Ten Ways to Fight Spring Dead Spot Disease.” The list contains turf management suggestions, including cultural practices, nutritional recommendations and pesticide treatments.
Spring dead spot disease is caused by three fungi that affect bermudagrass. As its name describes, it causes random brown patches that appear in the springtime. Symptoms usually show up in March or April and, with a cold and wet spring, the dead spots can persist into July.
Spring dead spot is typically a problem in the transition zone, where bermudagrass is cultured with a winter dormancy period. That encompasses thousands of golf courses and athletic facilities in states from coast to coast. In recent years, spring dead spot disease has been spreading, and now it’s showing up more often in putting greens, which naturally makes it more of a concern.
“It’s a devastating disease, and it seems to be getting worse,” says Dr. Bruce Martin of Clemson University’s Department of Entomology, Soils and Plant Sciences. “We can sort of tolerate it in fairways, although we’d rather not, but we’ve got a real problem when there’s a susceptibility to the disease in putting greens. It looks like some of the new Ultra Dwarf bermudagrasses are getting it as early as one year after establishment.”
Dr. Martin and others are intensifying their research on spring dead spot, because there’s still much to be learned about the problem.
“Somebody needed to do more work on how to manage this disease more effectively,” adds Dr. Lane Tredway of North Carolina State University. “When I arrived in North Carolina, clearly this was the primary disease problem in bermudagrass turf. But when I asked superintendents what they were doing about it most of them said, ‘Nothing.’ Over the years, this misconception had evolved that there was nothing they could do.”
To complicate the situation, many uncontrollable variables (such as temperature) affect the onset or severity of the problem, making it harder to find a solution.
“It’s a difficult disease to control, because it’s a root disease and we really don’t have enough information on exactly when the infections take place,” says Dr. Martin. “In general we know roots get infected in the fall, prior to the bermuda going into dormancy, and then the winter temperatures kill or weaken the infected grass . . . there’s not a lot of winter hardiness in bermudagrass.”
“Spring dead spot’s different because the fungus actually infects and parasitizes the plant,” explains Dr. Tredway, “and that makes the plant weaker and more sensitive to winter injury and freeze damage.”
“We preach preventive practices, but you don’t see the symptoms in the fall when fungicides need to be applied preventively,” continues Martin. “We’re trying to pinpoint when infections are taking place because then we can put our fungicides down in a more precise way.”
Fungicides are available to help control spring dead spot disease — some more effectively than others — but there are also many cultural practices you can use to prevent or minimize the disease damage. In fact, even the best fungicides generally aren’t enough to solve the problem alone.
The list follows.
1) Reduce nitrogen levels in the fall
Being a warm-season grass, bermuda doesn’t require much nitrogen before going dormant. Additional nitrogen supplied to the plant causes excessive foliage, which reduces the plant’s carbohydrate reserves and puts it in a more susceptible state heading into winter.
“That doesn’t mean going to zero,” says Martin, “it just means being judicious and weaning nitrogen out as you go into fall. You don’t want bermudagrass going into dormancy with a lot of lush growth.”
2) Provide ample potassium
“Potassium really does improve the winter hardiness of bermudagrass, and so in turn it reduces spring dead spot severity,” says Dr. Tredway. “You’re improving the overall health of the plant and sending it into winter in the best possible condition so it’s more resistant to the disease.”
Apply nitrogen and potassium in a one-to-one or a one-to-two ratio of actual N to K2O. Research has shown that a little more potassium than the grass can take up doesn’t provide better control, but a little excess potassium won’t hurt and is preferable to too little potassium.
3) Relieve soil compaction
Compacted soil can limit or prevent bermudagrass root growth, and if roots are infected with spring dead spot pathogens, there’s a greater risk of disease growth and turfgrass damage.
“The disease is always more severe in high-traffic areas where the soil is very compacted,” says Tredway, “so regular aerification is very, very important.”
4) Maintain proper soil pH
“On spring dead spot, we recommend that pH in the root zone be in the acid range, generally 5.0 to 6.0,” says Martin. “We have less trouble with the root zone in an acid pH, but it’s not absolute that if you got your pH down, you wouldn’t have spring dead spot.”
“The disease is definitely more severe as soil pH gets above 6.0,” agrees Tredway, “so it’s very important to maintain soil pH below 6 and preferably in the 5.5 range. The best way to reduce soil pH is with an acidifying fertilizer; specifically ones that contain ammonium as the form of nitrogen.”
5) Control thatch
When there’s a thick layer of thatch, turfgrass roots tend to grow specifically in that layer because that’s where the most moisture will be. If the grass won’t put a deep root system down into the soil, it can make the turf more prone to winter injury.
“It’s a pretty consistent relationship, where the more thatch you have the more severe the disease is,” explains Tredway. “Thatch is also an excellent environment for the pathogen to survive in through the summer, so the worse the disease becomes.”
6) Cultivate in spring to encourage recovery
In the spring, healthy bermudagrass tries to spread into the dead patches by establishing new roots in the affected soil. That process is aided by regular cultivation through spiking or hollow tine aerification, which breaks up the layer of dead turf accumulated in the patches and creates a more favorable environment for root growth.
7) Avoid DNA (dinitroanaline) herbicides in affected areas
Commonly used for pre-emergence control of crabgrass and other grassy weeds, DNA herbicides work by inhibiting cell division in roots. While very effective at controlling emerging weed seeds in healthy turf, DNA herbicides may not be the best choice for bermudagrass recovering from spring dead spot symptoms. .
“When the runners of the bermudagrass cross over these areas, normally they would tack down and root, but if you have those DNA herbicide residues there, they won’t,” explains Martin. “However, in healthy bermudagrass it’s not a problem, and those herbicides are used with good results.”
8) Improve soil drainage
Spring dead spot can be worse in wet areas, partly because the turfgrass doesn’t need to put down a deep root system, and because freeze damage and winter injury pose greater risks in wet conditions.
Reducing soil compaction increases water percolation down through the soil profile and good surface drainage also helps. In low-lying places that collect a lot of runoff water, it may be necessary to install a sub-surface drainage system.
“On the other hand, we see a lot of spring dead spot on higher, drier areas,” says Tredway. “You want adequate soil drainage for good plant growth, but with a very droughty mix, you might also have more spring dead spot.”
9) Apply preventive fungicides
Historically, most cultural treatments of spring dead spot have been reactive — only dealing with it after damage occurs to the turf. However, a fungicide applied in the fall can minimize the threat of spring dead spot by protecting the bermudagrass roots from fungal infections. Turfgrass plants treated with a preventative fungicide application are stronger and more resistant as they go into winter dormancy, so they come out healthier in the spring.
“There’s a pretty good amount of data out there,” says Dr. Martin, “and without a doubt the best has been Rubigan. fungicide by Gowan Company.”
“I would tend to recommend Rubigan,” agrees Dr. Tredway.
“Superintendents have applied it to bermudagrass for a long time, so it’s a product they’re comfortable with. I think the jury is still out and we have more work to do to optimize the rate and timing, but if a superintendent called me and wanted to treat for spring dead spot, I would recommend that he apply Rubigan at either 4 or 6 ounces twice in the fall.”
10) Relieve other stress factors.
A number of other stress factors can contribute to weakening bermudagrass turf and making it more susceptible to spring dead spot infection. Carefully manage mowing heights to levels that are consistent with the recommendations for your specific bermudagrass variety. Avoid excessive use of turf growth regulators (TGR’s) during the fall when preventative fungicide applications are being made. Keep a close watch on cultural and environmental factors that may be putting your turfgrass at risk of infection.
“Virtually any sort of stress on the plant from improper cultural practices is going to encourage spring dead spot development,” concludes Tredway. “You just need to make sure that you’re using good turf grass management practices.”