Phytophthora Crown Rot and Stem Canker
Friday, 05 May 2006 10:33
Calibrachoa cv .Million Bells Crackling Fire was diagnosed with Phytophthora crown rot and stem canker. Symptoms include wilting, decline, and plant death although a fairly healthy root system is present. 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 soilless 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.
Photos: Phytophthora crown and stem canker, 2
Bess Dicklow, UMass Plant Pathology Lab
