I have a dozen Phalaeñopsis plants that I nurture to rebloom. Earlier in summer found a sticky residue and what looks like little droplets on the stem. Also saw little brown ‘scabs’ on leaves. Wiped down with rubbing alcohol and put on veranda for 6 weeks, (north east facing 30th floor, Toronto).Cleared up. Brought in. Saw today new brown scabs on leaves and small what looks like water droplets on stem. Removed easily with alcohol swab. What is it and how to eradicate? New bud on one of effected plants. Many thanks.
Thank you for contacting the Toronto Master Gardeners.
From your description is sounds as if you have a scale infestation. Scale insects have a simple life cycle of egg, nymph (crawler), and adult. Indoors, eggs can be laid any time under the protective shell. The crawlers will look like tiny yellowish spots. The young soft scale produce a sticky substance called honeydew, which is the “water droplet” like substance that you are seeing.
Before you address this issue, be sure to move your infected orchid away from other plants to prevent the infestation from spreading. They’re frequently found on the undersides of the leaves near the middle vein of the leaf or on the edges of the leaf. They also commonly hang out on the flower stems.
Scale can be controlled by rubbing the infested areas gently with a soft toothbrush this will dislodge the sucking mouthparts of the scale or picking them off by hand. If the infestation is large, you may need to spray the plant with an indoor horticultural oil spray, which you’ll find at most good nurseries. Follow the instructions on the bottle carefully and you may need to repeat the treatment several times. It usually takes a month to six weeks to see any significant improvement. In particular, you’ll want to treat the tiny crawlers as it’s at this stage that scale is easiest to control.