Use nitrogen to combat dollar spot

The best way you can tell if your grass has dollar spot is to go out in the morning when dew is on the ground and see if there is a white cobwebby growth on the infected patches.

I cannot remember the last time dollar spot was such an issue during the middle of the summer.


Dollar spot shows up as small tan to brown patches in the lawn, mainly on zoysia lawns. The best way you can tell if your grass has dollar spot is to go out in the morning when dew is on the ground and see if there is a white cobwebby growth on the infected patches. Then look at the blades of grass up close and you should see small whitish or gray lesions reddish-brown margins.

This disease usually occurs when the nitrogen levels available to the grass are inadequate and when there are heavy dews, particularly in May and June, then again in September and October.

We cannot control the amount of rain we get, but the way you water the grass can help in control. Water early in the morning or at night and avoid watering from 4 to 7 p.m. Watering should be thorough, wetting the lawn to a depth of 6 to 8 inches, and as infrequent as possible.

Adding nitrogen fertilizer usually allows the turf to outgrow the problem. This is a leaf-blight disease and fungicides are rarely necessary. If you feel you have fertilized sufficiently and still have dollar spot, some fungicides you can use are myclobutanil (Fertilome F-Stop, Immunox), thiophanate methyl (Scotts Lawn Fungus Control), or maneb (Hi-Yield Maneb Lawn and Garden).

Also showing up a good bit in St. Augustine grass is gray leaf spot, which resembles dollar spot. They are straw colored with purple to brown margins. Severely infected blades wither and turn brown.

To help in control, do not overfertilize or overwater St. Augustine. it is very rare that the disease gets bad enough to warrant spraying. If you feel it is warranted, choose propiconazole (Ortho Lawn Disease Control, Fertilome Liquid Systemic Fungicide) or thiophanate methyl.

Armyworms can be a problem during even numbered years. So far it does not seem to be anything close to the problem we had two years ago, when they were the worst I had seen in 25 years.

If you have a Bermuda grass lawn or some variety of Bermuda pasture, you need to be on the lookout for them. I heard of some isolated cases in pastures and hayfields in south Richmond County. County agents are reporting them south of here.

The symptoms of armyworm damage are pretty straightforward if they are bad. You have a green lawn one day and almost overnight your lawn looks brown. The armyworms leave brown stems after they are through eating. With minor infestations, your grass will just look a little brown in some isolated spots in the grass. One sign that armyworms are in the turf is birds clustered on your lawn to eat them. You will also see a lot of gray moths flying around your grass at night.

Generally, the threshold level to treat is when you have five or more worms per square foot. If you suspect your turf is being infiltrated but can’t find the caterpillars on the grass, use a soap flush to bring them to the surface. Fill a 2-gallon bucket with water and squirt some dishwashing liquid it in (approximately a half ounce of dishwashing soap to a gallon of water.

Young armyworms are one-quarter to three-quarters of an inch long. Mature ones are one and a half inches. They are dark with several light stripes down the length of the body. The head or face has an inverted “Y” on it.

If you have to treat your lawn, carbaryl (Sevin), trichlorfon (Dylox), imidacloprid (Merit), cyfluthrin (Bayer Advanced products), bifenthrin (Ortho Max) and other pyrethroids are the best insecticides to treat with. Organic products include Spinosad and Bt. products (Thuricide and Dipel).

Irrigate before treating to move the caterpillars out the thatch layer of the grass. Treat lawns during early evening or as late in the day as possible when the worms are likely to be feeding. If possible, mow the grass before you treat then don’t mow for three days after the treatment.