There are a number of different types of mite, some clearly visible with the naked eye, such as the European red mite, and others visible only with a microscope, such as the Tarsonemid or cyclamen mite. The latter are the most common type found on begonias. Consequently, their presence may not be noted until after the damage to the buds and growth tips, where they live, has occurred.
Symptoms of a mite infestation are a cork-like substance on the stems of plants and the underside of leaves. The growing tips turn brown and become very brittle, collapsing when touched. Flower buds become distorted, and a brown stain is seen as the flower struggles to open. Plants can be decimated in a very short space of time, and the mites are often well-established before the symptoms are readily apparent.
Mites thrive in hot, dry conditions, so growing under glass heightens the risk of an infestation. Both high humidity and good ventilation around the plants will help prevent infection. Other plants known to be sources of mites should not be grown in the vicinity of begonias; these include cyclamen and strawberries. A wise preventive measure is to isolate new acquisitions, regardless of the source.
Insecticides: Note that insecticides are not effective against mites, and a proper miticide (acaricide) is required. Generally, the more lethal to mites, the more toxic the spray, so take full precautions when using the sprays.
Low-toxicity sprays may prove effective, perhaps largely because of the mites’ dislike of moisture. Seaweed products, which can also be applied as a foliar feed, keep the pests at bay, possibly because of the smell. Pest oil and wettable sulfur are other low- toxicity methods. Another non-toxic option is washing soda (sodium carbonate), using 1 teaspoon in 2 gallons (9 L) of cold water, plus a squirt of detergent. Plants can either be sprayed with this solution or totally immersed, if not too large.