Question 1

What is grease spot on a lawn?

Accepted Answer

Grease spot is a common name for Pythium blight, a fast-moving turf disease that leaves greasy, water-soaked, matted patches on the grass. The name comes from the oily, slimy look of the blades in an affected area. It most often hits cool-season lawns like tall fescue during hot, humid weather.

Question 2

How fast does Pythium blight spread?

Accepted Answer

Very fast. Under hot, humid conditions with warm nights, Pythium blight can damage or kill large areas of grass in about 24 to 48 hours, and highly susceptible grasses can sustain major damage in just two to three days. That speed is why quick, correct action matters so much.

Question 3

What does Pythium blight look like?

Accepted Answer

It appears as small, sunken, circular patches up to about a foot wide that run together into larger blighted areas. The blades inside look greasy and matted, colored orange to dark gray, and in the early morning humidity you can often see fluffy white or gray cottony mycelium on the grass. Damage frequently follows drainage lines and mower paths in streaks.

Question 4

Is Pythium a fungus?

Accepted Answer

No, not a true one. Pythium is an oomycete, also called a water mold, which is a different group of organisms from the fungi that cause most lawn diseases. This distinction matters because many ordinary fungicides that work on true fungi do not control Pythium.

Question 5

What kills Pythium blight?

Accepted Answer

Pythium blight requires fungicides made specifically for oomycetes, with active ingredients such as mefenoxam, metalaxyl, propamocarb, cyazofamid, or fosetyl-Al. Standard broad-spectrum lawn fungicides usually will not control it. Correct product choice, rate, and timing are critical, and rotating products helps manage the resistance that Pythium can develop.

Question 6

Will regular lawn fungicide stop Pythium blight?

Accepted Answer

Usually not. Because Pythium is a water mold rather than a true fungus, many common fungicides have little effect on it, so a generic product off the shelf often wastes money and precious time. You need an oomycete-targeted product, which is why getting the diagnosis right before treating is so important.

Question 7

What causes Pythium blight?

Accepted Answer

It is triggered by heat and prolonged moisture: night temperatures above 65F, daytime highs above 85F, and leaves that stay wet for 12 to 14 hours over several nights. Poor drainage, overwatering, evening irrigation, thick thatch, and lush growth from too much summer nitrogen all raise the risk. Outbreaks commonly show up the morning after a summer evening thunderstorm.

Question 8

How do you prevent Pythium blight?

Accepted Answer

Water only in the early morning before sunrise so the lawn dries fast, and never in the evening. Improve drainage, relieve compaction, and open up airflow so the canopy dries quickly, and avoid heavy nitrogen in summer, keeping applications under a quarter pound of nitrogen per 1,000 square feet when conditions favor the disease. On high-risk lawns, a preventive oomycete-specific fungicide program started once nights stay above 65F is the most reliable protection.

Question 9

Can Lawn Panther take care of this for me?

Accepted Answer

Yes. Our turf maintenance plans take the guesswork out of it — season-long weed control, fertilization, and pest and disease treatment on a set schedule by licensed applicators. Warm-season lawns are covered by our Bermuda and Zoysia maintenance plans, and cool-season lawns by our fescue maintenance plan.

Author: Ken Erickson

Pythium Blight in NC Lawns: The Fast-Killing Grease Spot Disease

Root Rot in Trees and Shrubs: Why Plants Wilt and Die in Wet NC Clay

Fire Blight in NC: How to Spot, Prune Out, and Stop It on Pears and Crabapples

Shrub and Tree Disease Treatment: A NC Homeowner’s Guide

Why Is My Evergreen Turning Brown? Needle Blight, Tip Blight, and Canker in NC

Boxwood Blight in North Carolina: How to Spot It, Stop It, and Save Your Shrubs

Powdery Mildew on Trees and Shrubs in NC: How to Spot It, Stop It, and Treat It

What’s Eating My Shrubs? A NC Guide to Leaf-Chewing Pests

Scale Insects and Mealybugs on Trees and Shrubs in NC: How to Spot Them

Sap-Sucking Pests on NC Trees and Shrubs: Aphids, Lace Bugs, Mites, Whiteflies

Gray Leaf Spot in NC Fescue Lawns: Spot It, Stop It, Save Your Grass

Dollar Spot in NC Lawns: How to Identify, Stop, and Prevent It

Services

Service Areas