By Ron McHatton with Photographs by Greg Allikas
Summer presents challenges in the form of increased pest activity, fungal and bacterial problems in traditionally wet areas and desiccation in those areas with Mediterranean-like climates where summers are typically quite dry. Careful observation of your plants is the best way to identify small problems before they become big problems, and in the summer, the time between these two events is dramatically shorter due to higher temperatures.
For small collections, the best thing to do is to physically wipe insects of and clean the plant. Isopropyl alcohol and a cotton swab are effective against most pests and if you want to increase its effectiveness, a drop of Ivory dishwashing liquid added to the alcohol helps wet the typically waxy surface of orchid leaves. If you haven’t been watching carefully and the infestation gets out of control, you might have to use chemicals. Few pesticides are specifically rated for use on orchids, but you can use any that are labeled for ornamentals. Use care and follow the label directions. This is not a situation where if a little is good, more will be better.
In areas with dry summers, mites can be a serious problem, especially on phalaenopsis. These creatures attack the surface of the leaves producing a sort of rough silvery appearance. Mites are not insects and insecticides offer little or no control. Mites do not like humid conditions so efforts to increase humidity are beneficial. Light infestations can be controlled by thoroughly cleaning plants but in hot, dry climates light infestations rapidly become serious and control is best accomplished by the use of a miticide.
In areas with wet summers, wet foliage and high humidity encourage the spread of fungal and bacterial diseases. Bacterial diseases do not respond to fungicides and vice versa so it’s important to know which disease you are dealing with. Perhaps the easiest way to distinguish between the two is by smell. The most common bacterial disease in orchids produces a foul smell often likened to dead fish. If you’ve ever had cut flowers stand too long in water, you know the sort of smell we’re talking about.
Diseases can spread quickly. Bacterial diseases kill plants especially rapidly and time is of the essence. Both bacterial and fungal diseases are spread by splashing water, and this includes rainfall. Use a clean cutting tool such as a single-edge razor blade, cut off the infected tissue as well as at least an inch (2.5 cm) of clean, green area and then treat the cut surface with a fungicide. Even if the problem is bacterial, you don’t want a fungal infection to start in the wound. Cinnamon — the common spice — is effective against fungal diseases and can be used to coat the cut surface. It’s perhaps not as effective as a chemical fungicide but it’s readily available and does work.
Where it’s wet, keep your plants as dry as possible. Alternatively, provide a lot of air movement. When you water, try to do so as early in the day as possible. This will allow adequate time for the foliage to dry before nightfall.
In dry-summer areas, the bane of orchid growers is extremely low humidity, and this leads to two issues. The first of these is an increase in the rate at which plants dry out and the other is the ever-presence of mites.