Orchid pests can be hazardous to your plants health...Part 2.It is a wise precaution in outdoor or window culture to tie a bit of cotton—about an inch or two thick and wide — around the base of new flower stems. For some reason slugs and snails won't crawl over the cotton to get to the flower bud. Even sow bugs and cockroaches are reluctant about crossing such a barrier. In tying the cotton barrier,keep it a fraction of an inch above the top of the compost. Nonabsorbent cotton, if it can be secured, is the best. However, if you have isolated benches and practice cleanliness, cotton on orchid flower stems is a confession of laziness.
The chances are better than a hundred to one that you will never be bothered by the cattleya fly, the dendrobium beetle larva, and the orchid weevil. They do serious damage, though, in some areas of the United States where large commercial orchid collections are maintained. Cattleya flies and dendrobium beetle larvae bury themselves inside orchid stems. You can detect them by blackened spots on the pseudobulbs. About the only cure is to dig them out and destroy them individually. The injured tissues are dusted with sulfur to protect them against rot. Before you start cutting up an orchid, have it checked by an expert. All black spots aren't caused by larvae. 
If you get any of the native orchid pests, the orchid weevil is the most likely invader. It is a small, black, shiny beetle which feeds lightly on buds and flowers. Its depredations are not extensive, but it causes the flowers to become spotted and unsightly. It lives in the osmunda when not out to dinner, and the job of killing it is not an easy one. Use a non-chemical insecticide and go after them on a warm morning when the temperature is 85° or better. Gardener's Supply Company - 15% off orders of $25 or more! Follow directions on insecticide labels for best results. If pesticide is in crystal form, don't let the crystals touch and burn the leaves. Place the treated pots in a closed Wardian case, blocked-off window, or closed greenhouse for the rest of the day. If the temperature goes up to 100 or more, don't worry. The warmth makes the crystals evaporate, forming a heavy gas that seeps down through the compost with a killing intensity. Be certain that the pots are dry before you begin treating your plants, and wait a day or two afterward before watering again. Bacterial rots are the inevitable result of poor culture. They are caused by a cold, damp atmosphere around the orchids. Wet rots, caused by cold water dripping from glass panes onto the plants, start out as a dark-brown discoloration on leaves. Soon the infected areas become black and water-soaked. Dry rots are caused by the same cold, damp conditions. But instead of developing soft, watery tissues, the affected areas become dry, hard, and filled with woody fibers. The treatment for both is identical: cut out the infection, dust with sulfur, and improve your culture.
Beginners often run into a third type of rot. Minimizing the importance of well-drained composts, they use heavy soils. Water left standing on top of the compost—not quickly draining off—will rot orchid rhizomes. The base of orchid pseudobulbs becomes semitransparent, gradually darkens, and the rot spreads through the bulb. The treatment is harsh and the cure uncertain. Lift the plant out of the pot, brush off the compost, cut away the rot, and dust with sulfur. Let the plant dry out for a day or so and re-pot correctly. Watch for any continued infection; there probably will be some, since the rot travels freely through the tissues. Always remember that the best you can do is never too much when it comes to pest control. You grow orchids not for their foliage but for their flowers. Similarly, most insects attack orchids for their flowers. You can win the struggle, but you must practice cleanliness, watchfulness, and prevention. Never give a bug a break. Once you have paid as much as $25 for a single plant, and then seen what a slug or snail can do to it, you'll know what we mean! Click here for part 1 of orchid pests.
|
