Mondo grass (Ophiopogon japonicus) that becomes discolored or grows poorly might be suffering from root rot. This dark green, grassy perennial grows best in moist, freely draining soil. Poor drainage and overwatering cause root rot, and slugs and snails can also attack mondo grass, causing wilting. Growing 12 to 15 inches tall and wide, mondo grass is hardy in U.S. Department of Agriculture plant hardiness zones 6 through 11.
Root Rot Symptoms
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Symptoms of root rot in mondo grass include leaf tip burn, yellowing and browning. Withered, brown leaf tips are the first sign of attack by a fungus called Pythium splendens, which causes root rot in mondo grass. The disease progresses down the leaves, and they turn yellow or brown. Finally, the leaves separate easily from the base of the plant when pulled.
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Treating Root Rot
Fungicides treat root rot in mondo grass, and applying compost can also help treat the disease.
A biological fungicide containing Gliocladium virens strain GL-21 controls Pythium splendens. Dilute the fungicide at a rate of 1/3 fluid ounce per 1 gallon of water, which treats 10 square feet of mondo grass. Apply the fungicide on a dry, still day when there is no rain forecast for 12 hours. Spray the solution evenly over the mondo grass.
Garden compost contains microorganisms that help control root rot. Evenly sprinkle compost over the mondo grass to create a layer about 1 inch deep. Gently work the compost between the mondo grass blades with your fingers.
Avoiding Overwatering
Root rot in mondo grass can be treated, but the disease returns in soggy, overwatered soil. Water mondo grass when the soil is dry to a depth of 1 inch. Spray water evenly over the grass until the soil is moist to a depth of 6 inches, but not soggy.
Controlling Pests
Slugs and snails can make mondo grass look as though it's dying. These pests chew holes in mondo grass leaves, which causes wilting. Control the pests with slug and snail bait. Search carefully between the mondo grass leaves for slugs and snails, and remove them before applying a slug and snail control.
Slug and snail bait granules containing ferric phosphate don't harm pets, birds or wildlife. Slugs and snails stop eating as soon as they eat the granules. Put on gloves, and evenly sprinkle the slug and snail bait granules on moist soil near the mondo grass, so that the granules lie 1/4 to 1/2 inch apart.