Lawn Diseases

lawn disease in a gainesville lawn

Information in this section is cited from the Florida Lawn Handbook.
https://edis.ifas.ufl.edu/features/handbooks/floridalawn.html
Florida Lawn Handbook, 2nd ed (2003)

Maintaining a healthy lawn can be a serious challenge for Florida property owners. Between pest problems and lawn diseases it’s not easy to keep your lawn in good shape. If you’ve noticed brown patches on your lawn or other symptoms of a lawn in trouble, contact McCall Service today. We’ll help you identify what type of lawn disease is to blame and our Lawn Care Services will restore your lawn!

Brown Patch Fungus

This lawn disease is most likely to be observed from November through May when temperatures are below 80 degrees F. It is normally not observed in the summer. Infection is triggered by rainfall, excessive irrigation, or extended periods of high humidity resulting in the leaves being continuously wet for forty-eight hours or more.

The fungus infects the leaf area closest to the soil, eventually killing the leaf. A soft, dark rot will occur at the base of the leaf, and you can easily pull a leaf off the stem. The base of this pulled leaf will smell rotted. Roots are not affected by this pathogen. The rotted base of the leaf is due to Brown Patch. This disease usually begins as small patches (about 1 foot in diameter) that turn yellow and then reddish brown, brown, or straw colored as the leaves start to die. Patches can expand to several feet in diameter. It is not uncommon to see rings of yellow/brown turf with apparently healthy turf in the center. Turf at the outer margin of a patch may appear dark and wilted.

This disease is often confused with herbicide damage on St. Augustine-grass. Herbicide damage may cause the same overall symptoms of yellow or brown patches. The leaf may still pull out of the leaf sheath, but the base of the leaf is not dark and rotted.

Irrigate only when necessary and do so only in the early morning hours (between 2:00 and 8:00 a.m.) when dew is already present. Since mowers can spread this disease, mow diseased areas last, and wash turf clippings off the mower before proceeding to the next site.

Helminthosoporium Leaf Spot

Turfgrasses Affected: All warm-season turfgrasses, but it is usually most serious on Bermuda grass. Different species of these fungal pathogens affect different species of turfgrass.

Occurrence: These diseases occur most frequently on Bermuda grass and include a group of fungi that are active over a wide range of temperatures. At any given time of the year, at least one species within this fungal group can be isolated. Thus, diseases caused by these fungi can occur at any time of year. However, as a general rule, the leaf spot disease occurs during mild, wet periods in fall through winter.

Symptoms/Signs: Leaf spot symptoms tend to vary with each pathogen/host pair from very small (pinhead size), solid brown to purple colored lesions or spots to expanded lesions with bleached centers that girdle the leaf blade. Severely infected leaves turn purple or reddish brown in color, giving the turf an overall purple cast. Severely infected leaves will eventually wither and dry to a light tan color. Distinct patches or patterns to the disease are usually not obvious. “Melting-out” occurs under severe infections as turf areas thin and die. Lesions on stolons are dark purple to black.

Grey Leaf Spot

This disease of St. Augustine grass is most often observed from late spring to early fall, especially during prolonged periods of rainfall. Excessive applications of quick-release nitrogen sources enhance disease severity, as does compacted soil. Initial symptoms include small pinhead-sized spots that are olive green to brown in color. These enlarge and form circular to oblong spots that are tan to brown colored with distinctive dark brown margins. Under humid conditions, the fungus produces abundant spores in the center of these spots, giving them a velvety gray appearance.

Many spots can occur on a single leaf, such that severely affected leaves wither and turn brown. No distinct patches are observed, but areas may appear thin. A severely affected turfgrass area may appear as though suffering from drought.

Once St. Augustinegrass is established in the landscape, the disease is chronic but not severe. During the summer months, individual St. Augustine-grass plants will always have a few spots on the leaf blades, but the overall health of the turfgrass is not affected unless the grass is placed under severe stress. Avoid excess nitrogen during potential disease development periods.

Do not use readily available forms of nitrogen such as soluble liquids or quick-release nitrogen sources just prior to or during these periods. Instead, use slow-release nitrogen sources. Apply a balanced fertilizer containing equivalent amounts of potassium, preferably a slow-release potassium form. If soils are compacted (walking paths, for example), alleviate the compaction or reduce traffic.

Pythium Root Rot

This root rot affects all warm-season turf grass. Symptoms are likely to appear any time of year but will always be associated with wet soil conditions. Poor drainage, excessive rainfall and poor irrigation can exacerbate the problem.

This root rot disease will result in a decline in turf quality and density however the turf seldom dies. Some areas or patches will turn yellow, light green or brown in color. This disease is often confused with herbicide damage on St. Augustine-grass. Herbicide damage may cause the same overall symptoms of yellow or brown patches. The leaf may still pull out of the leaf sheath, but the base of the leaf is not dark and rotted.

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