Brown Patch is a Cool Weather Disease in St Augustine Lawns

With the cooler temperatures and wetter soils, Brown Patch is active in lawns in the Pinellas County area. Brown Patch is a common turf disease that occurs in the Spring and Fall during cool (not cold) temperatures. The pathogen is a soil born fungus and can not be eliminated, but with some good culture can be reduced. Some lawns, because of the type of St Augustine and the soil, have chronic problems with Brown Patch. Distinctives are circles or joined circles of brown grass with a “halo” of yellow grass .

Cold vs. Deadly Disease

My experience with Brown Patch has me categorizing it as a “cold” as opposed to a “deadly disease”.

I think the “cold analogy” is a good one because:

Brown Patch generally will not kill your grass – unless it is near death to begin with.

It is temporary condition – Brown Patch thrives at moderate soil temperatures and as the soil temperature rises (or lowers), Brown Patch will cease to be a problem.

The causal agent is part of the environment – it is a soil born disease and cannot be eliminated.

Since it is not life threatening, I manage the Brown Patch with biological methods to reduce occurrences and treating only severe occurrences with commercially manufactured fungicides.

What to expect from Brown Patch

Brown Patch is a cold season disease of fall and spring. Brown Patch forms circles and/or lobed circles of tan/green weak turf that is flattened – like a round weight had been placed on the turf. The rings start out fist size and can grow to be 20 feet in diameter or larger. The outer edge of the ring (active area) is a multi-colored, mainly yellow in color, and is very distinct. Brown Patch responds to fertilizer - especially readily available nitrogen – by getting worse and to potassium by declining.

Also expect St Augustine to fully recover when cultural conditions improve – i.e. the weather warms or cools.

Treatment

Since the disease responds to fertilizers and is not lethal, manipulating fertilizers is the best management practice for controlling Brown Patch. To reduce the impact of Brown Patch during the cool season months I use slow, organic sources for nitrogen in very sparse amounts and high amounts of potassium. Manipulating fertilizer elements is “biological” control – and biological controls are very “green” in practice but slow to develop and weak in performance. Therefore in severe cases I will use a commercially available fungicide as a curative measure. In the 500 or so lawns I service, I only have about 5 that are problematic for Brown Patch and require fungicides; therefore the manipulating of the fertilizer elements is a good management practice for controlling Brown Patch.