The recent weeks of frequent heavy rains and consistently-hot and humid air have led to a proliferation of St. Augustine-killing fungus and armyworms. Symptoms include patches of yellowing and/or dead grass in an otherwise healthy lawn that increase in size and multiply after rains. Armyworms, which are actually a type of caterpillar, grow into yellowish moths that remain in the grass. Opportunistic weeds will invade if the fungus and/or armyworm infestation isn’t addressed.
An application of broad spectrum fungicide, immediately soaked in, followed by an application of bifenthrin a couple of days later, immediately soaked in, should eliminate the problem. (Note: Bifenthrin spray is more effective than bifenthrin granules. Fungicide should be reapplied after 3 months.) If the damage is minimal to moderate, a later soaking of potash will help the grass recover. If the damage is significant, the dead areas must be cleared and resodded. Make sure to apply bifenthrin, fungicide, and potash to new grass in stages.
It’s important to note that installing sod during cooler weather can mitigate the threat of mid-summer parasites.
Seth Mason, Charleston SC