Control these #"&*^ mites !By Dr. C. PasianDepartment of Horticulture and Crop Science The Ohio State University We have been recommending that you read the sticky traps (yellow cards) on a regular basis to have an idea of what insects are present in your crops and in what amounts. However, this technique doesn't work for mites. Mites do not fly so it is very difficult if not impossible for them to land on the sticky traps. This means that growers should inspect the crop itself in order to determine the presence of these destructive creatures. Furthermore, because mites do not fly, they may colonize in pockets. This means that crop inspections should be done with care. Remember that a problem crop is hanging baskets. Because of their location, many growers tend to avoid scouting them. Although bothersome, it pays to take down a few baskets (or climb a ladder to watch several baskets at a time). In other words, detailed SCOUTING is crucial. The easiest way to detect mites is through the web they spin. (Remember that mites are not insects. They are arachnids belonging to the same class as spiders and ticks.) Unfortunately, by the time you detect the web, the population of mites is very high and substantial damage to the crop has already occurred. To see mites in their different stages, it is necessary to have a 10X or higher magnifier. Mites tend to be found on the lower part of leaves. Feeding injury often gives the upper leaf surfaces a characteristic mottled or speckled appearance. They prefer hot and dry environments. Concentrate your inspections in the part of your greenhouse with these two characteristics. Spring often brings an explosion of mite populations soon after the first hot, sunny days. Among the numerous mite species, the most common in greenhouses are: the two spotted spider mite (Tetranychus urticae) and broad mite (Polyphagotarsonemus latus). Occasionaly, two other mites can be found on greenhouse crops: cyclamen mite (Steneotarsonemus pallidus) and Lewis mite (Eotetranychus lewisi). The cyclamen mite is very small and difficult to see even with a common magnifier. This mite produces leaf deformations. Mite size and diversity make the creature difficult to identify. It is important to identify at least the family because families share similar cycle and management. When in doubt, send a sample to the Plant Pest Diagnostic Clinic in Columbus (614-292-5006). As with thrips, an indicator plant system can help your mite scouting efforts. According to Dr. Lance Osborne, entomologist from Florida, it is possible to use Henderson bush lima. He recommends planting a few seeds in 4-inch pots and distributing them throughout the crop. Mites are attracted by these plants. These plants are also very useful if a bio-control program is used. Spider mite control on greenhouse ornamental crops is generally done using pesticides, but there are some excellent biological controls available. Finally, I suggest you read Dr.
Lindquist's article about mites on the web:
http://floriculture.osu.edu/archive/may98/smites.html
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