Whiteflies are a scourge that more and more gardeners are falling victim to. A world-wide problem, the use of insecticides has created a whitefly monster, immune to the most common pesticides and becoming more immune every year, until there will be a point where insecticides may no longer work. Insecticidal soap is becoming the most accepted form of control because pesticides are now known to go more than skin deep on fruits and veggies, it is safe to use, it produces results quickly and insecticidal soap is a solution that whiteflies cannot become immune to.
A tiny pest, they work in huge numbers to devastate your house plants, greenhouse plants, vegetable plants and the world’s food supply. Most of you will be the victim of the greenhouse whitefly, which is so-named because it is frequently seen in greenhouses, but is a major pest that attacks numerous fruit, vegetable and ornamental, both inside and outside. In fact, these thirsty pests not only feed on just about everything, they transmit any number of plant diseases. Tomato yellow leaf-curl begomovirus, TYLCV, is considered the worst, but they are attributed with spreading 60 different viral plant diseases.
In addition to the Greenhouse whitefly, the Silverleaf whitefly is becoming more prevalent. Your plants are likely to be attacked by either one of these species and though the physical differences may seem minute, the damage they are both capable of causing can be catastrophic. They often go unnoticed for a while because they attack the undersides of the leaves, staying out of the direct sun and out of sight, so the first preventative measure is to check the undersides of random leaves throughout your garden, especially on your tomatoes, squash and watermelons.
An adult female Greenhouse whitefly will lay an average of 50 to 150 eggs, and though the Silverleaf whitefly is smaller, she can lay up to 7 times the number of eggs that the Greenhouse whitefly can. The life cycle of both is also similar, growing from eggs, which hatch in 5 to 10 days, depending upon the temperatures, at which time a crawler emerges, travels a short distance and then starts feeding, which is when they start damaging your plants. From crawler to nymph to pupa takes about two weeks, and then the adult female will emerge from the pupa about a week later and will start laying eggs almost immediately. Her average life span is only 6 days, so she makes the most of it. She feeds with sucking mouth parts that extract the sap from the phloem of your plants. The phloem is the living tissue of your plants that carries nutrients throughout the plant. Without it, plant death can be quick to occur, but the warning signs are usually quite easy to spot:
- Yellowing leaves, yellow-spotted leaves and curling leaves can all be symptoms
- Eggs will normally be laid in a circular pattern and will either be opaque or slightly yellow, depending upon whether it is a Greenhouse or Silverleaf whitefly. The eggs will be laid on the undersides of your plants’ leaves.
- The nymph and pre-pupa stage will see the emergence of tiny white legs or fibers all around the small oval in the Greenhouse whitefly and not so much in the Silverleaf whitefly.
- As they reach pupa stage, they may appear to look like fish scales on the backs of your plants’ leaves.
- The most obvious sign is if you are enveloped in a white cloud as you bend down to inspect your garden. By that time, your infestation is probably quite advanced and at least partial plant death may be occurring. (Silverleaf whiteflies will be smaller and more yellow than white)
- Adults secrete honeydew as they suck the life out of your plants, and this will attract ants in droves; another sign to watch for.
- The honeydew that is secreted is the perfect growing medium for sooty mold, a black sticky mess that is impossible not to notice, but even more difficult to deal with than the whiteflies.
As stated above, there are pesticides to combat the problem for now. Just remember that every time you use a pesticide, you are contributing to a future generation of whiteflies that will be immune to the pesticide you use today.
We recommend, instead, organic means by which to control this stubborn and adaptable pest. There are, of course, natural enemies of the whitefly, such as green lacewings, ladybirds (ladybugs), minute pirate bugs, big-eyed bugs and damsel bugs. You can either buy them in egg form or as adult insects from commercial enterprises or you can plant plants that will attract them. Lacewings and ladybugs are both attracted to fern-leaf and common yarrow (achillea), fennel, dill and cilantro/coriander. There is more information here on which plants to grow in order to attract beneficial insects to your yard.
But, if you have a whitefly infestation to deal with now, you don’t have the time or the luxury to wait for plants to grow, or even if you buy plants already close to adult size, for the word to get out to the whitefly brigade of insect assassins to gather for the whitefly buffet in your garden. You need something now and you need something that will act quickly (remember, it only takes them about 3 weeks to go from egg to egg-laying adult).
The most common and safest organic method used is an insecticidal soap. You simply spray Safer Insecticidal Soap on the undersides of the infected plants’ leaves, either in the very early morning or in the late evening when the temperatures are below 85°F and when the whiteflies are not actively flying. It kills by penetrating the outer shells of these soft bodied insect pests, smothering, dehydrating and causing death in just a few hours. Insecticidal soap is non-lethal to beneficial insects and can be used indoors or out. A 32-ounce ready-to-use bottle will treat about a 1000 square foot garden plot. It is gentle on your most prized ornamentals but lethal for whiteflies and it has no unpleasant odor.
Whiteflies do not have to be the death of your garden. Besides ornamental, palms, weeds, poinsettias and countless other plants, the fruits and vegetables most affected are: Avocado, Cantaloupe, Carrot, Citrus, Cucumber, Eggplant, Gourds, Drapes, Lettuce, Peas, Pepper, Potato, Sage, Squash, Strawberry, Sweet potato, Tomato & Watermelon
Always look for whitefly infestation prior to bringing home new plants. It will save you a world of heartache. But, whiteflies can attack at any time, so we also recommend having insecticidal soap on hand, ready to do away with this pest before they have a chance to become a real problem for you.