If rust appears on ferns after harvest, the fungicide spray schedule recommended for management of Cercospora blight will also provide rust control. Stemphylium causes purple spot of spears and fern branches. Losses from this disease are from spotting of spears which reduces marketability. Stemphylium over-winters on fern residue. Spores that are released from infested residue initiate disease during spring.
Purple spot can be severe during cool, wet springs.
Twelve hours of wetness is necessary for infection and the disease is more severe with abrasion from wind-blown sand. Economic losses from purple spot have not yet occurred in Oklahoma. Purple spot symptoms on spears infected by the fungus Stemphyllium. Reference Sherf, A.F. and MacNab. This publication was originally produced 5-98.