Can spider mites kill or harm my houseplant?
Spider mites penetrate the leaf surface and remove the cell content. The result of spider mite infestation are tiny dots or stippling that give the leaves a bronze, chlorotic, grayish mottled look. Eventually the leaves will start to turn yellow/brown along the veins and drop. The foliage starts to wilt and general health of the plant declines. In severe infections you will also see fine webbing on the plant.
Test for spider mites
Take a white sheet of paper, place it on the underside side of the leaves and tap on the leaf. If you see tiny pindots moving on the paper, then you have spider mites.
Isolate your plant from all others because they reproduce rapidly (50-200 eggs in 7-14 days depending on temperature) and spread easily. If the plant is heavily infested then it should be discarded. It can be a difficult insect to control.
To control infestation
Spray the plant with insecticidal soap every 3-5 days for two weeks. Be sure to thoroughly cover the plant spraying the underside of the leaves. If insecticidal soap does not do the trick try Neem oil. An alcohol solution made of 4 parts of water to 3 parts of rubbing alcohol with a squirt of dish detergent can also work as a contact spray.
Spider mites can winter over in the soil. They love the hot, dry environment that is indoors during the winter and will attack plants that are stressed and weakened due to poor environmental conditions.
The solution is to alter the environment and sanitation-remove any infected dropped leaves. Increased humidity around the plant and washing the plant repeatedly with a forceful spray will knock off the mites and eggs which will help curtail the problem effectively but not eliminate it.
A note about insecticidal soap: A study at (ifas.ufl.edu) has found that some plants are sensitive to insecticidal soap causing phytotoxicity. The plant will show symptoms of yellow/brown spotting, burned tips, yellow or brown scorching leaf edges.
Some plants sensitive to insecticidal soap are ; gardenia, lantana, nasturtium, Easter lilies(when forming buds) , maidenhair fern and crown of thorns. In this case use a miticide for houseplants. Follow manufacturer label and be sure it is safe to use indoors.