Introduction

    Mites can be a very destructive pest in orchid collections. Mites are minute arthropods with four pair of legs. They are closely related to ticks, spiders, and scorpions. They are not true spiders, but some species spin fine webs to protect themselves and their eggs.They get the 'spider' part of their common name from webbing. They belong to the genus Tetranychus. The most common in orchid collection is Tetranychus urticae, of which one form is bright red, and others are yellowish or greenish; hence, the common name of red-spider. The mite's body contents (large dark spots) which are often visible through the transparent body wall , give the better known name of two-spotted spider mites.

   Mites can multiply quickly during be out of contol before you even notice them. When searching for spider mites, their fine webbing will likely be noticed first. Look on the undersides of leaves and between leaves for the webbing. These eight-legged pests are so tiny (about 1/50th of an inch), they are difficult to see with the unaided eye. For visual detection of the mites, a magnifying lens , or pocket microscope will be a big help. The presence of mites can be also be determined by rubbing a white cloth over the suspected infestation. If mites or eggs are present, reddish brown stain will be seen on the cloth. Another technique is to tap on a leaf over a sheet of white paper, then you may be able to see little moving specks on the paper.

    The spider mites and false spider mites are plant feeders. All mites have needle-like piercing-sucking mouthparts. They damage the leaves and pseudobulbs of orchids, by penetrating the plant tissue and suck the plant juice out. They are particularly troublesome on thin leaved orchids, such as members of the Oncidium Alliance, Cymbidium, and Cycnoches. However, they attack all orchids. They leave tiny white scars on the undersurface of the leaves, where they prefer to live. The result is a fine silver stippling of the leaf surface and the psuedobulbs.

   They are also injurious to the flowers. Their favorite point of attack on flowers is along the seams where the sepals come together in the bud, where they leave small transparent spots surrounding the punctured areas. One such spot is a blemish, but many spots actually ruin the flower. Sometimes as the sepals split apart, the mites enter the bud and cause enough damage to distort the flower.

Life Cycle

Hot, dry conditions are often associated with population build-up of spider mites, but infestations can occur anytime during the year. Under optimum conditions (70-80°F/21-27°C), most mites hatch in as little as 3 days, and become sexually mature in as little as 5 days. The females can lay upwards of 20 eggs a day, for a producing life of 2 to 4 weeks. The warm, dry conditions of greenhouses allows mite populations to survive, so infestations can occur even in winter.

Controls

• Mighty Wash® , which is a contact spray ready to use out of the bottle (do not dilute). At the first sign of mites spray plants leaves, fruits and flowers until complete saturation is achieved. If necessary spray at three day intervals. Mighty Wash® is statically (electrically) charged water which is safe to use on your orchids. The electrical charge when sprayed on kills the mites and their eggs. So safe, if used on vegetables can be used up to the day of harvest.

• Insecticidal soaps and horticultural oils, such as Neem Oils,or Safer's Insecticide Soap ® . Follow the instructions, and use in the cool of the evenings, not in the heat of the day.

• Since they are not insects, mites can not be controlled by normal insecticides. One reason that spider mites can become problems is the use of insecticides that destroy their natural enemies. Chemical controls generally involves miticides and acaricides, which are specifically developed for mites. Furthermore, their ability to rapidly reproduce multiple generations allows spider mites populations to adapt quickly to resist chemical controls. However, most miticides do not affect the eggs, so a repeat application at a 10 to 14 day period is usually needed for control, as well so alternate between different miticides and/or acaricides. Two-spotted spider mites can also develop a resistance to most acaricides after prolonged use.
  The best chemical controls are 1) Pentac, 2) Avid, and 3) Keltane. Follow manufacturer's instruction carefully, as chemicals do present dangers to humans and animals.

• Least effective, but sometimes, infestations can be reduced somewhat by frequent spraying of the orchid plants with water. Keeping the orchids well hydrated can keep the humidity up and the mites down.
  

These viciously destructive mites are also very small, similarily requiring a magnifying lens, to detect them. They are different from the spider mites as they do not spin webs. They also feed on top and bottom surfaces of the orchid leaves. They produce pits of dead tissue, which if the infestation is extensive, can cause the death of the leaf. The most often countered species are Brevipalpus californicus, and Tenuipalpus pacificus (the Phalaenopsis mite). All damage a number of orchids. Control is same as Spider Mites above.

RECOMMENDED READING

• All About Orchids, by Charles Marden Fitch
• Home Orchid Growing, 5th Ed by Rebecca Northen
• The Cattleyas and their Relatives, Vol. 1 by Dr. Carl L. Withner
• Growing Orchids - Book Two, by J. N. Rentoul
• Orchid of Brazil by Jim and Barbara McQueen
• Encyclopedia of Cultivated Orchids, by Alex D. Hawkes
• The Illustrated Encyclopedia of Orchids, by Alec Pridgeon