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Mealybugs
Symptoms: Mealybugs are sucking insects that attack any part of the plant but tend to stay tucked away at the junction of leaf and stem. Severe infestations cause chlorotic areas to appear on the leaves, which may darken, causing the leaf to yellow and drop prematurely.
Treatment: If there are only a few mealybugs, use a Q tip dipped in isopropyl alcohol or toothbrush dipped in a pesticide like Malathion, Orthene or Safer Soap (used per label instructions) to physically remove the mealybugs. For more severe infestations, apply the pesticide and repeat the application 2 weeks later. Be sure to spray all plant surfaces, particularly the undersides of leaves and leaf axils.
Prevention: Remove old leaf and flower sheaths to eliminate hiding places and allow easy inspection. Check new plants carefully before adding to the growing area.
Read More: Mealybugs on Orchids by Dr. Paul Johnson, Professor of Entomology at South Dakota State University.
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Spider Mites
Symptoms: Mites are not insects, they are members of the arachnid family. Mites typically feed on the underside of the leaves and can be found under the leaves as small, red to brown pests. A hand lens may be needed to see them. Leaf undersides may have webbing and brown splotches from the mite excrement. The upper surface of a damaged leaf may have a silvery sheen that eventually becomes sunken and turns brown. Leaves may be streaked, stippled or spotted due to lack of chlorophyll.
Treatment: Plants can be sprayed with a miticide like Kelthane following label instructions being particularly careful to contact all the undersides of the leaves. During warm weather, new generations mature every 6 days so repeat applications will be required, perhaps 3 applications at 4 day intervals. The Insect Growth Regulator TetraSan can also be used.
Prevention: Mites appear during warm, dry weather. Increasing humidity and leaf wetness and, if possible, decreasing temperature help prevent infestations.
Read More: Mites on Cultivated Orchids by Dr. Paul Johnson, Professor of Entomology at South Dakota State University and Mites by Susan Jones, American Orchid Society.
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Aphids
Symptoms: Aphids are sucking insects that attack buds, flowers and new growths and transmit disease from plant to plant. Buds and flower may fail to open and leaves may have a sticky deposit.
Treatment: Wash aphids away from the plant with a jet of water. Plants can be sprayed with a pesticide like Malathion, Orthene or Safer Soap using the product in accordance with label instructions.
Additional Info: The honeydew excreted by aphids and other sucking insects is attractive to ants and is an ideal medium for sooty mold. When sooty mold is present, inspect the plants for aphids, mealybugs, scale and mites.
Read More: Aphids and Their Control on Orchids by Dr. Paul Johnson, Professor of Entomology at South Dakota State University and Aphids by Susan Jones, American Orchid Society.
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Whiteflies
Symptoms: Whiteflies are small, moth-like insects that attack buds, flowers and new growth. The tell tale sign of whiteflies is a cloud of tiny white insects arising from an affected plant when it is moved or disturbed.
Treatment: Plants can be sprayed with Malathion, Orthene or Safer Soap following label instructions. Repeat applications at 4 day intervals until whiteflies are no longer present.
Prevention: Good sanitation and elimination of weeds will help prevent infestation as will keeping plant hosts separate from your orchids.
Read More: Whiteflies by Susan Jones, American Orchid Society.
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Snails and Slugs
Symptoms: These mollusks will leave holes and notches in the leaves, flowers roots and may chew off the growing tips. Chewed areas may also appear on buds. These nocturnal pests travel on a layer of slime and this slime trail is evidence of their presence.
Treatment: Chemical baits may be placed in the growing area. Ash and diatomaceous earth can be spread on horizontal surfaces to create a barrier though water will deactivate it. Beer in shallow tins can be spread in the growing area and the drowned pests removed the next day. Regular applications will have to be used because watering will disperse the controls.
Read More: Controlling Snails and Slugs by Dr. Martin Motes and Snails and Slugs by Susan Jones, American Orchid Society.
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Caterpillars
Symptoms: Caterpillars are the immature stage of moths and butterflies. While not common, they are voracious feeders that can do a great deal of damage to flowers and leaves in a short period of time.
Treatment: Caterpillars can be physically picked off the plant and destroyed, check the underside of leaves for their presence. Bacillus thuringiensis or Bt is a naturally occurring bacteria of insects, it is a safe and natural product that can be sprayed in the growing area following label instructions.
Prevention: Keep the growing area clean of fallen leaves and debris in which insect pests and their eggs can hide. Keep the landscape free of caterpillars.
Read More: Caterpillars by Susan Jones, American Orchid Society.
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Cockroaches and Grasshoppers
Symptoms: : Cockroaches and grasshoppers cause damage by eating flowers, roots and new growths.
Cockroach Deterrence: Cockroach baits can be spread in the growing area or a paste of boric acid, sugar and flour mixed with water can be spread in every nook and crevice you can find. Don’t get any of the stuff on the plants themselves. Another approach is to water and then flush a mix of liquid Sevin (1 tsp/gal) through the pot.
Grasshopper Deterrence: Crush the grasshoppers with a brick, shoe, etc. Partially bury jars filled with molasses and water and remove drowned victims the next day.
Read More: Roaches and Lubber Grasshoppers by Susan Jones, American Orchid Society.
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