Swiss Needle Cast

Phaeocryptopus gaeumannii (fungus)

HOST Douglas-fir

DAMAGE/SYMPTOMS Infected needles turn a dull green or yellow color, followed by browning of the needle tips. Older needles are usually more severely affected. Small, black spheres (fruiting bodies) emerge in parallel rows on the lower surface of infected needles. Brown needles drop over time with only the newest needles remaining on the tips of branches.

DISEASE CYCLE The fungus overwinters in infected needles. In spring, spores are released from the black fruiting bodies and distributed to newly emerging needles by wind and splashing water. New needles are primarily infected during cool, wet weather. After infection, needles may remain on the tree and produce spores for several seasons before being dropped.

MANAGEMENT Rake up infected needles and prune out and dispose of affected branches to reduce the disease source. Disinfect pruning tools between cuts with 70% ethyl alcohol or a standard household disinfectant spray. Provide good spacing between trees to optimize air circulation. Re-direct sprinklers to avoid hitting the tree canopy during irrigation. Affected trees can be treated with a fungicide containing the active ingredient chlorothalonil or mancozeb. Fungicides can only protect new needles; infected needles can’t be cured. Apply fungicides in spring when new needles have grown half their mature length. A second treatment should be applied three to four weeks later when new needles are full grown. Strictly follow instructions on the pesticide labels.

A Browning needles on Douglas-fir. B Discolored, infected needles. C Brown spots and yellowing of infected needles. D Dark fruiting structures emerge out of stomata of infected needles.