Peat moss helps control plant disease

Brown patch typically occurs in the fall. Occasionally, however, there are fleeting episodes in the spring. Distinct circular patches characterize its presence. Leaves are killed, but stolons (runners) aren’t. When long fall growing seasons prevail, new leaves may cover affected patches.

Cool night temperatures stimulate development and growth of the brown patch fungus. Sixty degrees is the triggering point. The disease window opens when night temperatures are cool enough to stimulate fungal development and closes when temperatures become cold enough to limit pathogen growth.

Expect brown patch development in high-maintenance lawns only. It almost never occurs in lawns that haven’t been fertilized or watered. It usually develops in St. Augustine grass lawns, but most other lawn grass species are susceptible, too.

Individuals who have high-maintenance lawns may choose from two options. They can prevent brown patch development by using fungicides or ignore symptom development once the disease occurs. Untreated lawns may be unsightly for a time, but they usually recover with no long-term effects.

Brown patch development may be light or heavy depending on the year. Control strategies are made more difficult by our not being able to predict the future. Brown patch can be prevented effectively with fungicide application. Terraclor (PCNB) and Immunox are two of the more effective materials. Ideally they should be applied at or just before symptom development. Individuals who wish to take preemptive action should watch fall temperature changes and apply a fungicide as soon as night temperatures drop to 60 degrees. Others may wish to take a wait-and-see approach.

Take-all patch bears no resemblance to brown patch, and it’s far more difficult to control. Chemical control often gives disappointing results. The most effective fungicides are expensive and available from commercial turf outlets only.

Take-all patch can occur anytime during the growing season, but its symptoms become most pronounced around the first of June and again around the first of October. Yellow irregular patches develop, followed by stand thinning. Stand loss may be substantial.

Don’t add fertilizer in hopes of improving the condition. Fertilizing makes disease damage more severe because the take-allpatch fungus causes root decay. Stimulating above-ground turf growth heightens the need for moisture. Restricted root systems can’t absorb enough moisture to accommodate the above-ground need. Affected plants die.

Sprinkling the affected area with a thin layer of Canadian sphagnum peat moss provides the best-known control to date. Phil Colbaugh, a Texas A&M plant pathologist in Dallas, researched the use concept. Peat moss stimulates beneficial bacterial growth, absorbs surface salts and provides mild nitrogen stimulation. This treatment has been more effective than fungicides on my lawn. It usually arrests further disease development.

Canadian sphagnum peat moss is readily available at nursery supply stores and isn’t expensive. Place the bale in a wheelbarrow, cut away the plastic casing and use a spade or scoop to crumble and distribute the crumbling moss. Apply a thin layer over the affected area only. Apply enough moisture to wet the surface if you wish. The thought of applying peat moss for disease control seems illogical, but it works.

• Wendell Horne is a retired Texas A&M University plant pathologist and consultant. His e-mail address is

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