Orchid Honeydew

Question

Can you tell me what the secretions are that some orchid plants put out around the stems of their flowers? Sometimes it is sticky and develops sooty mold like on Grammatopyllum scriptum. On other orchids, such as Oncidium Sharry Baby, it is more watery. I find it seems to appear in the morning.? —Tessa Harris

Anoles are fond of the sweet exude and can help prevent sooty mold by licking it from buds and flowers.

Answer

The secretion is simply plant sap, called honeydew, which is secreted by healthy plants. It is, as you note, basically sugar water, and can lead to sooty mold. This is why sooty mold can often be an indicator of sucking insects, which feed on this same sap, supplied to them by the plant’s osmotic pressure. When the pressure is sufficiently high, the sap passes right through the bugs’ digestive systems, resulting in conditions favorable for sooty mold. — Ned Nash