What’s That White Powder on Your Grass?
A white coating on grass blades can look serious, but it’s usually manageable. We’ll help you identify what it is and whether it needs treatment.
Symptom overview
What This Looks Like
A white, powdery coating on grass blades is almost always powdery mildew — a fungal disease that thrives in shaded, humid conditions. While it looks alarming, it’s usually cosmetic in warm-season grasses and manageable with the right approach.
Possible causes
What Could Be Causing This
Powdery Mildew
Powdery mildew is a fungal disease that coats grass blades with a white, talcum-like powder. It’s most common in shaded areas with poor air circulation and moderate temperatures. In Middle Georgia, it shows up primarily in spring and fall.
Gray Leaf Spot (Early Stage)
Gray leaf spot starts as small lesions with a gray-white center on grass blades. In early stages, the gray spots can look like a powdery coating, especially on St. Augustine grass. It progresses to blade death if untreated.
Learn moreSlime Mold
Slime mold appears as a dusty white, gray, or yellow coating on grass blades after warm, wet weather. Unlike powdery mildew, slime mold sits on top of the blade rather than infecting it. It wipes off easily and causes no damage to the grass.
Fertilizer or Pesticide Residue
Granular fertilizer or pesticide that hasn’t been watered in can leave a white residue on grass blades. This is easy to rule out — it appears immediately after an application and washes off with irrigation.
Diagnose it
Narrow Down the Cause
Is the white coating primarily in shaded areas of the lawn?
Powdery mildew is the most likely cause. It strongly prefers shaded, poorly ventilated areas. Improving sunlight and airflow reduces it significantly.
If it’s in full sun areas, slime mold or product residue are more likely than powdery mildew.
Does the white substance wipe off the blade easily with your finger?
Slime mold or product residue — both sit on the surface. Slime mold is harmless and disappears on its own. Product residue washes away with water.
If the white coating is embedded in the blade surface, it’s likely powdery mildew, which is an active fungal infection.
Was a fertilizer or lawn treatment applied in the last 48 hours?
The residue is likely from the product. Water the lawn to wash it in and the coating should disappear.
Product residue is ruled out. The coating is biological — either powdery mildew or slime mold.
Still not sure? A professional lawn assessment takes the guesswork out of it.
Get QuoteSeasonal timing
When This Is Most Common
Powdery mildew in Middle Georgia is most common in spring (March–May) and fall (October–November) when temperatures are moderate and humidity is high. It’s rare in the heat of summer because the fungus doesn’t thrive above 90°F. Slime mold can appear anytime after warm rain.
Common questions
Frequently Asked Questions
Will powdery mildew kill my grass?
In warm-season grasses, powdery mildew is mostly cosmetic and rarely causes serious damage. It can slow growth and thin the turf in heavily shaded areas, but it won’t kill established grass. Improving light and airflow is usually enough to manage it.
How do I treat white powder on my lawn?
For powdery mildew, improve air circulation by pruning low tree branches, reduce shade where possible, and avoid evening watering. Fungicide applications can help in persistent cases. Slime mold needs no treatment — just mow or hose it off.
Is the white powder on my grass harmful to my pets?
Powdery mildew and slime mold are not toxic to pets. If the white substance is from a recent lawn treatment, follow the product’s reentry guidelines (usually safe once dry, about 30 minutes for our products).
Related problems
Other Lawn Problems to Consider
Take action
Stop Guessing and Start Fixing
Every lawn problem has a solution. Get a professional diagnosis and targeted treatment plan from Attaboy Lawn Care.
