Controlling Pests in Your Garden With Nature: Whiteflies
By Nathan Jackson – Natures Control
Oregon Cannabis Connection
The Pest: Whiteflies
Tiny white “moths” resting on the underside of leaves. When the leaf is disturbed the whiteflies flutter around and quickly settle back onto the leaf.
Whiteflies are not the most common cannabis pest around, but they can be very destructive. They are more common indoors and in greenhouses, but some outdoor growers get them too. They are very hard to get rid of once their breeding population gets large, so it is best to get control of them as soon as they are found.
Whiteflies are not true flies from the insect order Diptera; rather they are from the order Hemiptera. They are related to aphids, mealybugs and scales (a common citrus pest occasionally found on cannabis). They get their name from the white wax that covers the adults’ wings and body. Whiteflies are sap-suckers—feeding on juices from the plant by using piercing mouth parts. As they feed, they secrete a sticky substance called honeydew. The sticky honeydew promotes mold growth, so it should be regularly washed from the leaves. Whiteflies can also spread diseases from plant to plant— which can cause unusual growth and a whole variety of problems that can be hard to diagnose.
There are many species of Whiteflies, but the most common for cannabis growers is the greenhouse whitefly (Trialeurodes vaporariorum), followed by the sweet potato whitefly (Bemisia tabaci). Both species look similar, but have a slightly different shape to their wings and some subtle differences in their nymph stages.
When whiteflies reproduce they lay small oblong eggs on the underside of the leaves. After the eggs hatch, they will grow through four stages called instars. The first instar (crawler) is very tiny and very hard to see without a good scope. The crawler moves around the plant, eventually finding a spot to feed. Later instars do not move and have a flattened oval appearance similar to scale insects. After the final instar, a winged adult emerges ready to mate and start the cycle again.
There are many natural predators of whiteflies. Whitefly parasites (Encarsia formosa) lay their eggs inside developing whitefly pupae. The parasite feeds on the pupae and eventually a new whitefly parasite hatches out, instead of a whitefly. Encarsia formosa are most effective against greenhouse whitefly, but some new variants such as the nile delta Encarsia formosa work against a broad range of whitefly species. They are commercially available on cards that can be hung from the foliage. Whitefly parasites typically emerge within a few days. You know they are working when the whitefly pupae turn black after they are parasitized. Eretmocerus eremicus is another commercially available parasite similar to the Encarsia formosa.
Whitefly predators (Delphastus pusillus) are small black beetles that love to eat whiteflies. They can devour up to 600 eggs per day. Delphastus have a preference for sweet potato whiteflies, but they will eat many different species. Many growers use them in combination with the parasites. General feeding predators such as green lacewings and pirate bugs are also known to help fight whiteflies. They are good to have in the garden to help prevent many small soft-bodied insects. Amblyseius swirskii (russet mite predators) are also known to attack some stages of whitefly.
While whiteflies are not as common as spider mites on cannabis, they can be just as destructive. One or two can turn into thousands in just a matter of weeks, so it is important to keep an eye out for them. Keep some good bugs on your plants all the time to keep your plants as healthy as possible.
An ounce of prevention is worth a pound of the medicine.
© 2017 Oregon Cannabis Connection. all rights reserved.
Nathan Jackson is the owner of Nature’s Control and Ladybug Indoor Gardens. Located in Phoenix, Oregon, Nature’s Control has supplied growers with beneficial insects for over 35 years. He can be reached at 541-245-6033 or firstname.lastname@example.org.