Dear Docs - September 9
I have a few dendrobiums outside, and ever since the rainy weather I have noticed something looking like soot on them. What do you think caused that and what should I do?
This soot did not just happen. It has been building up for some time. Sooty mould is actually the excretion of a sucking insect called an aphid. The aphid population usually increases during the dry season. Like humans, the plants are susceptible to disease (fungus) when they are not watered or fed properly.
As you don't seem to have a great many orchids, I am suggesting you use some dishwashing liquid with a little cooking oil to wipe the leaves (the way they grow).
Sooty mould might not kill the plant right away, but leaving it untreated will reduce its ability to breathe properly, or to absorb the chemicals and fertiliser. If left untreated for a while, the plant will in fact start to lose its blooms.
If you wish to use a fungicide, you will need to also use an insecticide to get rid of the insects that bring the sooty mould. The most effective fungicide contains copper, which when placed in direct sunlight will burn the orchids. Therefore, you need to protect them from direct sunlight. CHAMPION and Caprid will work wonders. This you will need to use once per week for four to six weeks.
I received an orchid as a gift for my birthday recently. It has a tag with the name epidendrum. I know nothing about orchids. Can you advise me how to care for my orchid?
Epidendrum orchids prefer the cooler areas of your garden, and like a lot of water and fertiliser. Most of them do not like soil. Notice whenever they are planted in soil they tend to walk out. Please try a mixture of charcoal, tree fern bark and pebbles. Always have osmocote at the root, (a time-release fertiliser). They will reward you during the cooler months, usually from October to spring.
Betty Ashley is an avid orchid enthusiast who has spent decades successfully cultivating orchids for herself, as well as for orchid lovers across the island, earning herself the title 'Orchid Doc'. Send your orchid questions and/or concerns to: firstname.lastname@example.org.