Whiteflies

Marijuana Horticulture

by Jorge Cervantes

Identify

The easiest way to check for the little buggers is to grab a limb and shake it. If there are any whiteflies, they will fly from under leaves. Whiteflies look like a small, white moth about 0.04 inch long. Adult whiteflies have wings. They usually appear near the top of the weakest plant first. They will move downward on the plant or fly off to infest another plant. Eggs connected with a small hook.

Damage

Whiteflies, like mites, may cause white speckles, stipples, on the tops of leaves. Loss of chlorophyll production and plant vigor diminishes as infestation progresses.

Cultural and physical control

Mites are difficult to remove manually because they fly. Adults are attracted to the color yellow. To build a whitefly trap similar to flypaper, cover a bright, yellow object with a sticky substance like Tanglefoot. Place the traps on the tops f the pots among the plants. Traps work very well. When they are full of insects, toss them out.

Biological

The wasp, Encarisa formosa, is the most effective whitefly parasite. The small wasps only attack whiteflies, they do not sting people! All toxic sprays must be washed off completely before introducing parasites and predators. Since the Encarsia formosa is a parasite, about 0.125 inch long, smaller than whitefly, it takes them much longer to control or even keep the whitefly population in check. The parasitic wasps lays an egg in the whitefly larva that later hatches and eats the larva alive, from the inside out – death is slow. If you use them, set them out at the rate of two or more parasites per plant as son as the first whitefly is detected. Repeat every two to four weeks throughout the life of the plants.

The fungus Verticillium lecanii AKA Cephalosporium lecanii, trade name Mycatal, is also very effective in whitefly control.

Sprays

Easily eradicated with natural sprays. Before spraying, remove any leaves that have been over 50 percent damaged and cure with heat or burn infested foliage. Homemade sprays applied at five to ten day intervals work well. Insecticidal soap applied at five to ten day intervals. Pyrethrum (aerosol) applied at five to ten day intervals.