Gray leaf spot as common in Lowcountry as Shrimp and grits

  • Tuesday, July 9, 2013

With the recent rain and pop up thunderstorms, gray leaf spot, downy mildew and other diseases have been flourishing in the area. Japanese Beetles have also gone to town on our ornamentals, especially roses and crepe myrtles.

Mosquitoes are going crazy – monitor your yard for areas that collect water and drain them, preventing the mosquito from breeding.

Gray leaf spot (Pyricularia grisea) goes with St. Augustine like grits go with shrimp. Or like chinch bugs go with St. Augustine. To battle gray leaf spot you are best employing many cultural practices and using limited control products if necessary.

Gray leaf spot looks like someone burned or dripped acid on the leaves of the plant. There are little oblong spots on the leaf. Eventually, these spots grow together and the leaf blade dies. Whole areas of your grass can disappear at once when these leaf blades die.

Culturally there are several things to do to minimize your problem with gray leaf spot. This disease likes high humidity and excessive nitrogen fertilizer. To help alleviate the high humidity, mow your grass to a level that seems abnormal to St. Augustine. Try to get it down to teo and a half to three inches depending on the variety of St. Augustine grass.

Also try to mow every three to five days with a bagger. This mowing will help get sunlight down to the crown of the plant, drying the leaf blades as quickly as possible. Skip the gym and mow.

Gray leaf spot likes hot humid weather. Minimize the amount you water as much as possible. Wait until your lawn is getting a blue/green color and your foot prints stay in the lawn after you walk across it before you water. Unfortunately, you can not control rainfall as easily. In the Lowcountry, afternoon thunderstorms are a way of life, so keep the grass mowed as low as you can so it will dry out quickly.

Since the Lowcountry dries out very quickly when the rain stops, the use of a wetting agent like Possum’s Wetting Agent with Biostimulants will help reduce supplemental watering.

Using wetting agents also helps reduce the amount of dew that remains on the leaf blade. Dew can really make diseases spread. On golf course greens we would go out with a dew whip to get the dew off the leaf blades of the grass. A dew whip is a very long fiberglass pole that would slide across the top of the grass, knocking the dew off of the blades of grass so the grass would dry.

Hold off of the nitrogen fertilizer until you can get this disease under control. If you need some color you could add a product like Possum’s Minors to give you some green without all the nitrogen.

A healthy lawn is less apt to get diseased and recovers more quickly from any pests that might damage it.

Having a soil test done and following a program to get the nutrients that the test recommends is an easy preventive step that you can take to improve the overall appearance and health of your yard. Do you need potassium, magnesium?

With the conditions as favorable as they have been, a preventive application of Disarm would be a good idea (this product will give you up to 28 days control). If you have to resort to a control product, make sure the product is labeled for Pyricularia grisea.

There are many leaf spot diseases on labels of control products but only certain ones work on gray leaf spot on St. Augustine.

We had one customer come in that had been applying a product that controlled Drechslera spp. and Biopolaris spp. leaf spot; however, the product was not labeled for Pyricularia grisea (watch where you shop).

Honor Guard, Disarm, Cleary’s 3336 and Heritage are systemic products that you spray. Since this is a leaf spot fungus, the sprays seem to give good coverage over the leaf blade.

If you insist on a granular product, Prophesy G (same active as Honor Guard and Banner), Cleary’s 3336 G or Disarm G are granular systemic products that will do a good job for you. When controlling a leaf spot disease, rotate your chemicals.

Whether you spray or use a granular, these products will come up through the root system. Always read and follow product label.

I’m already way over my column inches for the week, so I guess Japanese Beetles can wait until next week.

At the three Possum stores, we send out emails to people on our email list when we get an outbreak of insects or disease, are having gardening talks or any other relative information.

Just go by the store and sign up – that easy – and it is free. We also promise to protect your privacy and not bombard your inbox. We also post updates on the website at www.possumsupply.com.

Always read, understand and follow product label. The product label is a federal law.


Bill Lamson-Scribner can be reached during the week at Possum’s Landscape and Pest Control Supply. Possum’s has three locations including one at 481 Long Point Road in Mount Pleasant (971-9601). Bring your questions to a Possum’s location, or visit us at http://www.possumsupply.com. You can also call in your questions to “The Garden Clinic,” Saturdays from noon to 1 p.m. on 1250 WTMA. The Horticulture Hotline is available 24 / 7 at possumsupply.com.

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