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Our lawns have had a much better season than last year. Most areas have received a bit of natural irrigation and the warm temperatures have helped our grasses fill in and recover. Keep a good thing going as we slide toward fall by adding potassium and be prepared to knock large patch out before it kills parts of your lawn.
Potassium, the last number of the three on the fertilizer container, is the Rodney Dangerfield of plant nutrients. It just doesn’t get the respect that nitrogen and phosphorus receive. Maybe that’s because potassium applications don’t cause visual responses in the grass, but adequate potassium levels are important in maintaining the health of your lawn.
Adding extra potassium each September is especially important in coarse-textured, sandy soils. When it comes to holding on to nutrients, these soils are rather like a bucket with a large hole in the bottom. Stuff just runs out. While phosphorus will hang around and build up, nitrogen and potassium get washed through in water.
In centipede, St. Augustine and zoysia lawns that aren’t due for any more nitrogen this year, use a straight potassium product. In most cases sul-po-mag (0-0-22) is preferable. Applied at 5 pounds per 1,000 square feet, it provides the necessary potassium and has a side benefit of adding extra magnesium to the mix. Some folks use potassium sulfate (0-0-50) at 3 pounds per 1,000 square feet. That works but it’s pretty difficult to apply 3 pounds on 1,000 square feet evenly.
Bermuda lawns, especially the hybrids, will stay greener through the fall with a small application of nitrogen in September. Instead of the straight potassium product, consider a fertilizer like 5-5-15 at 10 pounds per 1,000 square feet. That provides one-half pound of nitrogen and the extra potassium to help the grass survive the coming winter cold.
While you’re out working on the lawn, remember the fungal disease large patch likes to get going as the temperatures moderate. Like most fungal diseases, large patch likes it moist. Keep a close check on areas where water tends to collect.
Large patch first shows up as irregular, straw-colored areas where the grass blades collapse. Usually the stems are still healthy and green. When the fungus is really working, you may see a ring of reddish-brown around the perimeter of the patch. This disease, caused by the fungus Rhizoctonia solani, is an equal opportunity grass killer. All of our warm-season grasses are susceptible even though you will often see it listed as “zoysia patch” in references.
Research in southeastern North Carolina suggests a fungicide application in early September and repeated in about six weeks is most effective in controlling large patch.
Products containing azoxystrobin (Heritage), myclobutanil (Eagle), propiconazole (Banner Maxx), thiophanate-methyl and triadimefon (Bayleton) are labeled for large patch control. Although the fungus is active in spring, fungicides don’t work as well then.