YARD NOTES · PEST ALERT
Armyworms & Large Patch.
Two problems that can erase a lawn in about a week. One is an insect that eats the grass down in a few days and usually grows back. One is a fungus that takes the crown and does not. Telling them apart fast is most of the job, so here is how.
PEST ALERT · FALL 2026 · TWO MINUTE READ
THE TEN-MINUTE TEST
1 — Two tablespoons lemon dish soap.
2 — Two gallons of water.
3 — Pour over one square yard.
4 — Wait ten minutes.
5 — Count what comes to the surface.
Do this before you buy anything
Clemson’s soap flush is the standard scouting method and it costs nothing. Mix one to two tablespoons of lemon-scented dish detergent into one to two gallons of water, pour it over a square yard at the edge of the damage, and wait. Armyworms come to the surface within ten minutes. If nothing comes up, you do not have an insect problem, and an insecticide will not fix whatever you are actually looking at.
How to know it is a fall armyworm
The larvae reach about an inch and a half and range from green and yellow to brown and grey, so color will not tell you anything. The tell is on the head: a yellow-to-white upside-down Y. They feed in early morning and late afternoon, which is why people find a lawn that looked fine at lunch chewed down by dinner.
Why they seem to appear overnight
They do not — you just could not see them yet. More than 93 percent of everything an armyworm eats is eaten after its fourth larval stage. Most of their life does almost nothing visible, and then the whole population reaches the stage where it eats at once. Scouting beats reacting by a wide margin here.
The good news about armyworms
They eat leaf tissue, not crowns and roots. An established, healthy warm-season lawn that gets chewed in September usually comes back. What it cannot do is come back well if it is heading into winter underfed, poorly drained, or already thinned by disease — which is the real reason two lawns on the same street recover differently.
Large patch looks nothing like it
Large patch appears as circular or irregular patches that expand outward, often with a darker, water-soaked edge, and the grass pulls loose easily at the base. There are no caterpillars, and a soap flush brings up nothing. It moves in cool, wet weather rather than heat. Centipede is the most susceptible turfgrass in South Carolina, followed by St. Augustine and zoysia.
What actually prevents it
Three things, and none of them are a product. Keep fertilizer off warm-season turf after August 15 in the mid-state. Water no more than once a week in spring and fall, in the morning rather than the evening. Do not let thatch build up. Fungicide does work in fall — two applications about three weeks apart, starting once soil temperature drops to 70°F — but it works a great deal better on a lawn that is not already being set up to fail.
Not sure which one you have?
Send a photo. We will tell you what we think it is and whether it needs anything at all. Call or text (803) 343-9655, or use the contact form. If it needs a soil test before anyone treats it, we will say that too.