What is Pythium?
Pythium Blight in turfgrass is a destructive disease that can kill large areas of grass if left untreated. In the Maryland / Virginia area, Pythium generally presents itself when temperatures are hot and humid in summer. The pathogen can lay dormant in the soil from the previous year, and it spreads primarily through the presence of surface water caused by poor drainage or heavy rainfall. This article discusses how to identify, prevent and also how to get rid of pythium blight.
Pythium is fairly easy to identify. Look for gray or purple "fuzz" growing on grass blades in the infected areas. After one or two days, you will see small patches begin to die off completely, ranging from the size of a golf ball to about 4". Left untreated, the disease will continue to spread through water or through mechanical means (such as your mower).
Pythium is sometimes confused with Brown Patch, which is a less severe disease that attacks Tall Fescue and Kentucky Bluegrass. Brown patch is generally less severe (only partial browning) but infects larger areas. Pythium appears in smaller patches but completely kills the plant (completely brown).
The easiest method of control is prevention. Ensure that your turf is properly drained and that water does not pool during rainfall or irrigation. You can apply a fungicide as a preventative measure in the middle of summer, but you need to ensure that it is labeled to control pythium. Also, try not to mow wet grass, as this could spread a minor infection in one area into your entire lawn.
If you discover a pythium infection, it should be treated immediately with a fungicide. Whereas other types of turf fungus will slowly damage your lawn over the course of a few weeks, pythium can kill large areas within 1-2 days. Spray the surrounding areas with a liquid fungicide to limit its spread.
Once cooler weather returns in September, any damages areas should be renovated with fertilizer and seed. Pythium will no longer attack turfgrass in the Mid-Atlantic once night-time temps drop back into the 60s.