Over the past week, we have noticed some disturbing signs in our orchid houses. The phragmepidiums and paphiopedilums have more yellowing leaves than usual, and the cattleyas and even the phalaenopsis orchids have some scale. Oncidiums and some cattleyas bulbs are showing some brown, soft tissue at the base signifying rot. This is the result of the weather, which has been rainy and humid while the light has turned the corner and become less intense winter light.
Without good air circulation in these days of high humidity, rain and shorter days, orchids are susceptible to such poxes and pests.
Examine your orchids carefully and reduce your watering schedule. Look into the crevices between leaves for scale; look under leaves for scale when yellow spots appear on top of them. Watch for black rot at the base of pseudobulbs on cattleyas and oncidiums, and fungus (brown areas surrounded by a yellow halo) on all plants. Have cinnamon or alcohol at hand. If the ends of leaves turn brown, cut away the area and treat the cuts with a Captan paste. If you cut out rotting pseudobulbs, treat the remaining good tissue with Captan paste.
In this month’s orchid newsletter, Martin Motes recommends using hydrogen peroxide on vandas and phalaenopsis with crown rot. Hydrogen peroxide comes in various strengths: 3%, 5%, 8% and 35%. Use 3 percent. You will see the bubbling characteristic of hydrogen peroxide. Treat daily until you see no more bubbles forming.
|Edema, but not a disease.
(Hydrogen peroxide can be used as a spray to prevent fungal and bacterial disease. Spray it weekly on orchid leaves in the growing season or in weather such as we are experiencing now.)
Because the recent days have been hot, you may have forgotten to reduce the amount of water you are giving to your plants. Suddenly, cattleya and dendrobium leaves are showing black markings that scare you to death. It is edema, swelling of tissue caused by the plants receiving too much water. There is nothing you can do about it now; just cut back on the water. It's not a disease!