Lawn Disease and Fungus Treatment in Southwest Florida

How to Tell Disease From Insect Damage

These get confused constantly, and the treatments have nothing in common, so it is worth two minutes to narrow it down before calling anyone.

Look at the shape. Disease usually appears in roughly circular patches that expand outward, often with a distinct edge and sometimes a darker or orange ring at the boundary. Insect damage is more irregular and tends to spread in the direction the insects are moving.

Look at the individual blades. Pull a few from the edge of the patch. Fungus-damaged blades often have lesions or spots partway up, and the base where the blade meets the runner looks rotted and pulls apart easily and sometimes smells. Insect damage is either chewing, with notched blade edges, or a blade that died intact.

Look at the timing. Large patch and brown patch turn up as the weather cools. Chinch bugs peak in the heat. If your problem showed up in November, fungus is more likely than chinch bugs.

Look at where. Disease favors shade, low spots and areas that stay damp. Chinch bugs favor the hottest driest sunniest part of the lawn. The two are usually in opposite corners. 

Large Patch and Brown Patch

The main cool-season disease in this area and the one we treat most. It is the same fungus, Rhizoctonia, and it becomes active when soil temperatures fall below roughly 80 degrees, which around here means late October through winter and into early spring.

It shows as roughly circular yellow to brown patches, from a foot to many feet across, expanding outward. The edge is often distinct and can look orange or reddish in the outer ring. Inside the patch the grass may look thin rather than fully dead, and it can partly recover in the middle while the ring keeps expanding.

The tell is the blade base. Grab a blade at the edge of the patch and pull. With large patch it separates easily from the runner and the pulled end looks dark and rotted rather than snapped or chewed.

The most common cause we find is evening irrigation. It is also driven by too much nitrogen going into cool weather, excess thatch, and anything that keeps an area damp and shaded.

Gray Leaf Spot

A hot weather disease, so it runs opposite to large patch. It hits St. Augustine hardest through the summer rainy season, when it is warm and humid and the lawn stays wet.

It shows as small oval or diamond-shaped lesions on the leaf blades, grey to tan in the middle with a darker brown or purple border. On a badly affected lawn the whole area takes on a scorched grey cast and thins out.

It is often worst on newer sod and on lawns that have been pushed hard with nitrogen, because fast soft growth is more susceptible. Shaded areas with poor air movement get it worse.

Backing off the nitrogen, improving airflow and watering in the early morning does a lot of the work. Severe cases need treatment.

Take-All Root Rot

The one that gets missed, because everything you can see about it looks like something else. The damage is below ground.

Above ground it looks like irregular yellowing and thinning that does not respond to fertilizer or to water, and it often shows up in summer after a stretch of heavy rain even though the damage started months earlier. Homeowners usually treat it as a nutrient problem for a season first.

The diagnosis is in the roots. Dig up a section from the edge of the affected area and look at them. Healthy St. Augustine roots are white and firm. With take-all they are short, dark, and rot away easily, so the plant cannot take up water or nutrients regardless of how much you apply.

It is strongly associated with stress: compacted soil, high pH, poor drainage and turf that has been under pressure from something else. Recovery is slow because the plant has to rebuild a root system, so this is a season-long project rather than a single treatment.

Dollar Spot and Fairy Ring

Dollar spot appears as small bleached patches roughly the size of a silver dollar, which can merge into larger areas. Individual blades show a straw-coloured lesion across the blade with a darker border. It is associated with lawns that are underfed, particularly low in nitrogen, and with heavy dew. It often responds well to correcting the fertility rather than to a fungicide alone.

Fairy ring shows as a ring or arc of darker, faster-growing grass, sometimes with mushrooms appearing along it after rain, and sometimes with a dead or thinning band. It is a soil fungus breaking down organic matter underground, and the ring is where it is working. It is more of a cosmetic problem than a turf-killer in most cases, and it is genuinely difficult to remove completely because the fungus is in the soil, not the plant.

We will tell you honestly when a fairy ring is best managed rather than chased.