Spider mites are tiny sucking insects which remove the chlorophyll from plant tissue, leaving damaged leaves and stems. Black flies are a species of aphids that have a similar damaging effect. There are green, yellow and black varieties of aphids. Damaged plants look weak and the leaves become yellow. There are several methods for eradication and preventative controls of these pests.
There are estimated to be 1,375 species of aphids, black fly being one of them. They are often identified by their colors of green, yellow or black. Black flies thrive in moist environments and they attack any succulent new growth on a plant. Black flies are less than 1/8 inch long, with two tubes which extend from the end of their body. These tubes are partially responsible for the secretions they use as a defense mechanism. Spider mites are a microscopically small mite with a two-part body.
Spider mites attack woody ornamental plants such as azaleas, camellia, hibiscus and roses. They leave fine, web-like substance on plants as they eat. Plants attacked by spider mites look bleached and the leaves stippled. Black flies gather in colonies on the underside of plant leaves, producing a "honeydew" substance as residue. This is called "sooty mold."
Black flies weaken the plant structure by sucking the sap out of it.The stems look weak and black "sooty mold" fungus is on the leaves. Ants are then attracted to the fungus. Damage from spider mites creates dried out looking leaves with yellow or brown spots and a web-like substance between the leaves. Black flies can spread the cucumber mosaic virus, which is damaging to tomatoes and other plants.
Spider mites can be eradicated with several types of insect spray. Use a garlic-chili-pepper-soap spray or a mixture of coriander oil and water. A spray of buttermilk, potato flour and water in a thin mixture will suffocate spider mites. Both spider mites and black fly can be sprayed off plants with a forceful spray of water. To control black flies with spray, use rhubarb or elderberry leaves. The oxalic acid compound in these plants kills insects.
Green lacewings, praying mantis and ladybugs are natural predators to spider mites and black flies. They are available in quantity from the garden center or by mail order. Place in the garden in early morning or evening. Companion planting is also a preventative and there are many plants which emit odors and compounds which are repellent to black flies and spider mites (see Resource). If plants are heavily infected they should be dug up and composted.