Question of the Week – Number Two: July 16, 2020

“How can I tell the difference between damage of chinch bugs and damage of gray leaf spot?”

To know which problem has beset your St. Augustine (gray leaf spot can also attack zoysia), you need to learn to look closely for symptoms.

Chinch bugs…
Prime symptom: Damage will always appear in hottest, sunniest parts of the lawn.
They will return to the same areas each summer, generally showing up by mid-June or early July.

St. Augustine in full sun has been attacked by chinch bugs. (Photo posted on my Facebook page by Travis H.)

Prime symptom: Grass will appear dry, but will not respond to irrigation.
They can quickly kill affected areas.

Blake Layton of Mississippi State University posted photos of various stages of chinch bugs to help us know when we see them.

• Prime symptom: BB-sized black insects with irregular white diamond-shaped markings on their wings. Nymphs are small, red.
They will be on the surface of the soil around the grass runners. You can see them if you part the blades of grass with your fingers and look for them on hot afternoons.
Treat with labeled insecticide granules or spray. Your local independent retail hardware store or nursery will have several options. You may only need one treatment per year.

This lawn in McKinney, as seen last August, probably had to be resodded this year. Chinch bug damage was that severe.

Continued Below

Gray leaf spot…
Hot-weather fungus that shows up first in mid-June through late summer. (Symptoms of take all root rot are similar, but they show up in April and early May when it is much cooler.)

Catherine W. posted this photo earlier this week on my Facebook page asking me to confirm that it was gray leaf spot. (It is.)

Prime symptom: Individual blades will have BB-sized grayish-brown lesions, usually on the midribs of the blades and occasionally on the runners as well.
Will show up in both sunny and shaded parts of lawn.

When I say that “gray leaf spot shows as yellowed washes within the lawn,” you can see them in this photo from Sandra S. that she posted to my Facebook page a couple of years ago.

Prime symptom: Affected areas will appear as yellowed washes of grass when you look at your lawn from the side.
This disease is exacerbated by nitrogen. Avoid feeding your lawn during the hottest part of the summer.
The fungicide Azoxystrobin (sold at consumer level as Scotts Disease-EX and to commercial applicators as Heritage) offers control for current outbreaks, but avoiding nitrogen in summer is the better solution.

Posted by Neil Sperry
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