Helminthosporium disease is a set of plant diseases affecting turfgrass in North America during the colder months. Also known as melting out, leaf spot, and net-blotch, this lawn disease is caused by fungal infestation, particularly of the Bipolaris, Drechslera, and Exserohilum genera. At least one species in this set can find its way into turfgrass at any time of the year, but the disease usually breaks out in the fall or winter, specifically during mild, wet episodes.
Aside from diminishing a home’s curb appeal, helminthosporium lawn disease involves the production of spores during the growing season, infecting not just wet leaf blades but possibly humans who inhale them in considerable quantities. The lawn care experts at Fairway Lawns can help treat helminthosporium and other turf diseases so you can enjoy a beautiful, healthy yard! Contact us today!
Favorable Conditions for Helminthosporium
Helminthosporium disease progresses faster when hot, dry weather cycles with extended periods of humidity, typically in temperatures ranging from 30 to 85 degrees F. However, spores can be produced and infection can occur only when the leaf has been wet for long hours, such as during evening irrigation, on cloudy days, or when air movement is limited. Situations traumatic to the turf, such as droughts and excessive traffic, create a perfect environment for the disease, along with the heavy use of nitrogen fertilizers.
Helminthosporium Disease Symptoms
Many things play a role in the development of symptoms of Helminthosporium disease, including the particular fungus and grass species involved, the weather, and even cultural factors.
Common symptoms include the appearance of thin, lifeless patches of grass, but each type of turfgrass can have more characteristic ways of showing infection. For example:
Kentucky bluegrass and tall fescue leaf blades initially develop dark purple or black spots. They later become light brownish yellow in the middle and are lined by a dark brown to dark purple shade around the sides.
Bentgrass can look soggy and matted, with smoky blue sections about 1-4 feet in diameter.
Bermudagrass often gets tiny purple and black spots all over, from the stems to the leaves, where the discoloration grows bigger and lighter at the center while the borders remain a purple shade.
When conditions are warm and moist (usually from 60 to 85 degrees F), necrotic spots or streaks may be seen on infected leaves, accompanied by seed rot, a phase in plant infection called blight or blighting. When conditions discourage growth, the disease may finish the entire cycle over a few days, with certain areas of the turfgrass fading into a light brown hue.
Helminthosporium Prevention Tips
Correct and consistent turfgrass maintenance can help prevent helminthosporium from developing in the first place. Here are some tips for preventing this lawn disease:
Avoid herbicide applications as well as excessive nitrogen and potassium applications
Test leaf tissue regularly to ensure that nitrogen to potassium ratio is maintained at 1:2
Control stress when conditions encourage disease development, such as by raising mowing heights or distributing traffic across the area
Provide just enough moisture to keep the turf from drying up during hot weather
Water occasionally but deeply (turf needs about an inch of water, whether rain or supplemental irrigation)
Avoid evening or late afternoon watering, which keeps leaves moist for longer periods
Ensure effective surface and internal drainage when conditions are wet or moist
Have helminthosporium fungicides regularly applied for disease control
Maintain a grass height of 2.5 to 3.5 inches without cutting off more than a third of the current growth
Gather and destroy infected leaves and clean the mower frequently to remove contaminants
Keep the mower sharp at all times as dull blades can lead to ragged cuts that create entry points for pathogens
While the above measures cannot stop an ongoing helminthosporium infection, they go a long way in preventing it, especially when taken during the early stages of the disease. The best way to manage an infection is with help from a professional lawn care provider!