Bermudagrass is one of the most widely grown turf species in the warmer zones of the U.S. Unfortunately, it’s susceptible to more than its share of diseases.
When bermudagrass becomes infected with a fungal disease, rarely will a single fungicide application produce desirable results. A much more effective strategy is to employ multiple methods to manage overall disease levels and produce a quality playing surface.
The IPM route
The first step in an effective integrated pest management (IPM) program is to identify the actual malady. In addition to fungal diseases, many other causal agents adversely affect bermudagrass, including management and environmental stresses such as chemical damage, mixing and application errors, soil compaction, drought, heat, high soluble salt levels, drought, cold and heat. Many aids are readily accessible to assist with correct identification.
Websites assembled by many land grant universities in the South are a good start. Books by well-respected plant pathology authors are excellent references as well, and can often be found at discounted prices from vendors such as Barnes & Noble and Amazon. The more time spent studying disease symptoms, the better.
Once correctly identified, the other parts of IPM can be utilized to reduce disease pressure and reliance on fungicides. Bermudagrass can be a heavy thatch producer, so take steps to reduce the rate of buildup and lessen the potential for infection, because the fungus will survive more easily in leaf debris.
Cultural practices that affect deep rooting also are important in an IPM program; proper watering, aerification, balanced fertility and mowing height can have a pronounced impact on the growth and expansion of the root system, which increases the health and vigor of the turf.
Spring dead spot
Caused by Ophiosphaerella korrae and Ophiosphaerella herpotricha, spring dead spot is very descriptive of this disease. As the turf breaks dormancy in spring, circular patches ranging from 6 inches to 2 feet in diameter remain dormant.
Upon close examination, the roots, shoots, stolons and rhizomes usually are dark and rotten in these affected areas. In most cases, the patches recur in the same location each year, often increasing in size. As the spots grow, the centers often become invaded by weedy grass species and/or broadleaves, producing a ring-like appearance.
Spring dead spot infection results in a major disruption in the uniformity of the playing surface. Tebuconazole, azoxystrobin and fenarimol provide a moderate degree of control.
Another very aptly named disease is dollar spot (Sclerotinia homoeocarpa). On closely cut putting green and tee-box turf, it appears as a bleached to light tan spot the size of a dollar coin. As the height of cut increases, so does the size of the spot, with spot size growing as large as a baseball in the rough and higher-cut turf.
Inside the affected areas, distinct lesions appear on leaves that remain erect. The lesions have white centers and reddish-brown borders; they usually cross the entire width of the leaf blade.
On greens, the lesions are not nearly as distinguishable, usually appearing as a tip dieback, later turning white to tan. In these areas, the grass may be killed to the soil surface, with spots developing in a merging pattern. In early morning, fuzzy white mycelial growth commonly is evident.
Many products are effective for dollar spot control, including boscalid, chlothalonil, fenarimol, fluazinam, iprodione, metconazole, myclobutanil, propaconizole, tebuconazole, thiophanate-methyl, triadimefon and vinclozolin. Resistance to the DMI, also referred to as triazole fungicides, has become more common with this disease, so use multiple modes of action in the fungicide rotation.
Sometimes referred to as brown patch, large patch is caused by Rhizoctonia solani, the same disease that affects cool-season turfgrasses. Large patch appears as mostly circular sections of affected turf ranging from yellow to tan and light brown.
Large patch is the given name, as these areas are 2 to 3 feet in diameter at first, often expanding to 10 feet or more. As turf in a given area becomes heavily infected, these patches often coalesce to form larger patches.
A tell-tale sign is the patch margin, which usually is reddish-orange to bronze. Individual plants in the affected area often have reddish-brown to gray lesions on the leaf sheaths. Leaf removal sometimes is needed to fully observe the symptoms.
Azoxystrobin, fluoxastrobin, flutolanil, PCNB, penthiopyrad, pyraclostrobin, tebuconazole, triadimefon and triticonazole have been shown to provide good to excellent control of large patch.
Leaf spot/melting out
Leaf spot/melting out, caused by Bipolaris cynodontis, is favored by cool and wet periods in the fall and spring. In the early stage, leaf spot symptoms appear, and, when uncontrolled, the pathogen moves quickly into the lower portions of the plant, killing the crown, and produces the “melting-out” stage. The leaf spot lesions are small oval brown spots on the sheaths and leaf blades. As they grow, the center becomes tan, bordered in dark brown to black. As they become more numerous, they grow together and cause entire plants to die.
In the melting-out stage, reddish brown color is common, as well as a softening of the sheaths, crowns, rhizomes and stolons, leading to wilting and foliar dieback. Melting out usually appears in a scattered or irregular pattern in bermudagrass turf.
Several products are effective against melting out, including azoxystrobin, fludioxonil, fluoxastrobin, iprodione, mancozeb, penthiopyrad, pyraclostrobin and vinclozolin.
Microdochium patch/ pink snow mold
Pink snow mold, Microdochium nivale, develops during winters with snow cover. Symptoms become evident as the snow melts in spring. Roughly circular sections of turf, 3 inches to a foot in size that are white to light tan with a salmon-pink-colored border, are characteristic. Infected leaves within the patch usually are matted down.
In periods without snow cover but extended cool wet weather, the leaves take on a reddish-brown to salmon color and greasy appearance. As the disease symptoms are being actively expressed, the patches often are surrounded by a bronze-colored ring.
Several fungicides have shown to be effective for pink snow mold control, including fludioxonil, iprodione, PCNB, penthiopyrad, thiophanate-methyl and trifloxystrobin. Areas prone to this disease should be treated prior to winter so the fungicide can be absorbed into the plant tissues.
Pythium root rot
Pythium root rot, sometimes referred to as Pythium root dysfunction, is a tough-to-control, persistent disease, especially in compacted, poorly drained areas. It can be exacerbated by over-irrigation, where soil voids fill with water.
This disease generally does not produce clear, distinct foliar symptoms, but a yellowish to orangish cast when viewed from a distance.
Heavy infections of Pythium will express themselves near pockets of saturated soils. If Pythium is suspected, roots and rhizomes should be closely inspected. When infected, these tissues appear soft, dark and greasy to the touch. As well, depth and density of the root system are greatly reduced in areas affected by Pythium root rot.
A few fungicide products can prevent damage from this disease, including azoxystrobin, cyazofamid and pyraclostrobin. Watering the product down into the root system in critical when trying to manage this disease with some fungicides, so make sure to read the label directions for product use.
A quickly developing malady of bermudagrass and many cool-season turfgrasses is slime mold. Appearing as small and rounding patches with dusty leaves, individual leaves can be covered with masses that are gray, purple, yellow, black or orange.
Slime mold isn’t an actual fungal disease, per se, but an organism related to Myxomycetes. Fortunately,it doesn’t cause direct harm by infection; however, it blocks sunlight to the leaf surface, causing mild damage and yellowing of the leaves.
Generally, slime molds aren’t considered harmful, but they can be a good topic of coffee-table discussion with non-golf industry friends.