Cymbidium with Black Spots and Mites: Dual Treatment

Cymbidium Black Spots and Spider Mites

Vivian's Cymbidium Chung Ruby has large black spots near base of new shoot and older pseudobulb. Leaves mottling, yellowing. Sentimental plant (tribute to father). She hasn't repotted recently. Photos included.

Expert Response

Vivian, most orchids need annual repotting. If not done, roots suffer, lower mix decomposes, stays damp, causing root rot and fungus—blackened areas at base. Two-part process: get fir bark mix. Unpot, remove infected sheaths, rinse roots. Use copper fungicide (Kocide) at recommended dose, submerge roots and base for an hour. Remove stringy/lifeless roots first. Dry plant on paper. Clean pot or use new one. Use mix dry (not soaked). Copper leaves green staining, shows coverage, prevents further infection. Water weekly with leftover fungicide solution until gone, then normal watering. Feed when new growth appears.

Follow-Up: No Copper Fungicide, Mites Discovered

Vivian can't find copper fungicide in Toronto (stores closed/limited). Has sulfur spray and powder. Leaves worsening, losing color; sees tiny moving white/brown specks—likely spider mites. Asks if sulfur fungicide works and what to do about mites.

Second Response

Vivian, sulfur spray is best. But first address mites: photo shows spider mite damage on leaf underside. Tiny sucking mites multiply rapidly, cause damage especially on undersides. That's likely the "specks." Need miticide specifically for spider mites, several applications over weeks. Systemic miticide also works. Mites thrive in late fall/winter when indoor humidity drops. Garden centers likely have miticides. First, remove most damaged leaves/portions (mites concentrated there). May take a month+ to control. Isolate Cymbidium, check other houseplants. Mist between sprayings to increase humidity. Once mites controlled, start sulfur fungicide.