Phalaenopsis Problem

Question

Three of my phalaenopsis plants have developed a kind of white, sticky, fuzzy goop on their leaves, front and back. One also has a spike with buds, and this goop seems to be on the spike as well. I assume this may be some kind of fungus. I have washed it off, sprayed the plants with a fungicide, and separated them from the other plants, but the problem remains. —Melissa Harris

A serious mealybug infestation on an orchid leaf; photo © G.Allikas.

Answer

Based on your description, my first guess would be mealybugs, which, if bad enough, do lose their individuality and look like the white goop you describe. Phalaenopsis are more susceptible to mealybugs than most orchids, because they grow faster and are, therefore, softer and tastier to sucking insects. Mealybugs particularly like the flower spikes, and are especially difficult to eradicate, as they will hide under the bracts covering the nodes. Your best bet if the infestation is as bad as you say is to spray the plant with a pesticide such as malathion at label strength. Do it now before buds begin to initiate, or the plants may suffer some floral deformation. It will take two or three treatments at seven- to 10-day intervals to curb the problem. Try to watch your plants more closely so that the infestation does not progress to this point, as it will be easier to treat and can be treated with a less-invasive pesticide, such as insecticidal soap or horticultural oil. —Ned Nash