Are you engulfed by a white cloud of flying bugs every time you touch, or walk by a certain plant in your yard? Are you discouraged from trying to control these bugs because nothing seems to work? What are these insects that seem to be sucking the life out of your favorite flowering plants and vegetables?
This pest of summer vegetables and herbaceous ornamentals is one of the most resilient summer pests; it is known as the Whitefly.
Whiteflies (Trialeurodes vaporariorum) feed on the underside of leaves. The adults and immature whiteflies eat by sucking fluids from the host plant. Whiteflies are parasites to plants, and should not be ignored. Whiteflies are known to transmit more than sixty viral plant diseases. They cause leaf damage and can cause leaf death; eventually causing the death of the host plant. Just like aphids, whiteflies produce honeydew which is a sticky residue that is attractive to ants. Ants can interfere with proper predator control, thus allowing the population of whiteflies to increase. The honeydew sap also gets covered with black sooty mold and is very unattractive. If the mold is present on fruits or flowers it can cause them to be unsalable. Whiteflies love warmer temperatures and thrive between 80 and 90 degrees Fahrenheit. They also attack over five hundred different varieties of plants, and may or may not stay on their primary host. They produce offspring very efficiently and can take over entire plants in a matter of days.
There are many different types of whiteflies, the most common being Greenhouse and Sweet Potato/Silverleaf whitefly. The average adult whitefly lives approximately fourteen to twenty five days, females having the shortest lifespan. Each adult female lays between 80 and 300 eggs in her lifetime. The eggs hatch and crawlers emerge, quickly finding a vein on the underside of a leaf from which it can suck. The crawler then turns into a nymph which molts four times until it becomes an immobile pupa; this process takes about three weeks. The adult whitefly hatches from the pupa and continues to feed on the host plant, and produce offspring.
The best and most effective way to control whiteflies is by using spray-on *pesticides, though whiteflies are not easily controlled with any of the available pesticides. Whiteflies are very resistant to pesticides. The adult whitefly is even more resistant than the immature ones. When a wet pesticide has dried it does not effect the adult whiteflies. Thus several applications of a wet pesticide must be used, over a long period of time. Some *pyrethroid pesticides are effective and sometimes only one application will be required. Pyrethroid pesticides are generally harmless to humans. Pyrethroid breaks down in about two days by sunlight and other environmental factors. *Neem oil or *narrow-range oil are good ways in which to kill whitefly nymphs; though the plant must be thoroughly covered in order for it to work.
There really is not a reliable and effective way to kill whiteflies organically. Most organic pest-killers have proven to be ineffective at controlling all the stages of whiteflies. The only way to get rid of them organically is to physically wash plants or spray the underside of leaves with a soap spray -- but this has not been shown to be an effective cure, unless the pest problem is very small.
Calendula (like Marigolds) and Nasturtiums are said to trap and repel whiteflies; these are known as companion plants. Companion plants play a very important role within a garden or ecosystem. Marigolds are one of the most beneficial plants to a garden, they repel a large variety of pests.
A technique not involving pesticides of any form is called biological control. To control whiteflies biologically one must release a large amount of natural predators to whiteflies. These predators include, but are not limited to: Ladybugs (Coccinella septempunctata), tiny parasitic Wasps (Eretmocerus eremicus), Green Lacewings (Chrysopa perla) and more. When predators are released in enough numbers they can control whitefly colonies -- though this does not completely eradicate them. Yellow sticky traps can also be used to capture adult whiteflies; but this does not kill immature whiteflies.
*Warning: Pesticides are poisonous and you should always take care and caution when using them. Always read carefully the instructions before using pesticides. You should check to see if the vegetables can be eaten after being sprayed, if you are spraying a vegetable plant. Root-type vegetables differ from vegetables that grow above ground, so be diligent in reading the instructions and warnings. Keep away from children and pets.
Also it should be noted that by using extreme amount of pesticides you will be killing all insects, both good and bad in your garden area.
General note: be careful when photographing these pests, as they tend to fly around when disturbed. A larger quantity of whiteflies flew out towards my camera lens and got themselves stuck in the lens until I released them. Check equipment after exposure and shake off clothing so you don’t bring the flies into your home -- as they will attack houseplants.
Source for pictures: Angela (me)