Needlecast Diseases of Evergreens: Identification and Fungicide Timing

Overview

Needlecast diseases of evergreens are caused by several fungi. Much remains to be learned about infection timing, latency period, optimal fungicide timing, and best chemicals. However, progress is being made. Infected needles generally fall several months after actual infection. Greatest infection period for most needlecast fungi: late spring/early summer. Symptoms (visible indications) appear late winter, spring, early summer of the next year.

All needlecast fungi form small structures on infected needles producing thousands of spores. Fruiting structures may be black, orange-red, or tan depending on fungus. Other saprophytic fungi on dead/dying needles may form similar structures—finding a fruiting structure on a dead needle is not proof of needlecast. Send sample to Plant Disease Clinic for verification.

Managing Needlecast Diseases

Needlecast fungi require abundant moisture. Plant for good air circulation. Maintain weed control to prevent tall weeds impeding airflow around lower branches. Avoid planting susceptible trees in low/shady areas where humidity and needle wetness remain high. Fungicides protect healthy new foliage. Even if sprayed, needles infected previous year and showing symptoms this year will fall off. But new, protected needles will be symptom-free next year and remain on tree. For most needlecasts, fungicide applied as new needles emerge. See specific fact sheets on pine, Douglas-fir, and spruce for details.

Rhabdocline needlecast symptoms on Douglas-fir; Swiss needlecast on Douglas-fir needle; Rhizosphaeria needlecast on spruce; Cyclaneusma fruiting on pine (aphid injury left, Cyclaneusma banding right); Lophodermium fruiting on pine needle; Dothistroma on pine (photo courtesy M. Concklin).