BLIGHT--CREEPING MYRTLE, PERIWINKLE, VINCASudden death or thinning of vinca groundcovers usually is caused by a canker disease that infects the stems, girdling the plants.
Vinca blight can be minimized by regular yearly mowings in the spring,
with the mower set on it's highest settings. Rake and compost all clippings/cuttings.
Fertilize and water to stimulate new growth.