Symptoms of Phytophthora root rot, crown rot and stem canker include wilting, decline, and plant death . Phytophthora like Pythium is a lower fungus favored by excess moisture and excess nitrogen fertility. Unlike Pythium, species of Phytophthora are more aggressive, more likely to be host specific, and less frequently found in greenhouses. The most likely source of origin is plant material. Start with soil-less growing media and avoid contaminating growth medium with soiled hands, tools, or flats. Promptly remove diseased plants,avoid splashing water when irrigating, and keep hose ends off the floor. The best means for controlling Phytophthora crown rot and stem canker is with drenches of systemic fungicides which will move up into crown area such as mefenoxam (Subdue Maxx), foestyl-Al (Aliette),azoxystrobin (Heritage), or phosphonate-Al (ProPhyt). Check label for crop appropriateness. These fungicides should be rotated by chemical class to prevent resistance development.
Fact Sheet: Root Diseases of Greenhouse Crops
