Q. I am new to gardening in the desert and am surprised at my success thus far! That is, until the whiteflies came. It is August and they are on EVERYTHING!! I started with insecticidal soap on the undersides of the leaves and I see dead flies there. I am getting ready to plant all new Vegetable crops for fall but need to get a handle on these flies before subjecting new plants to these insatiable pests.
A. Whiteflies are a very tough insect to control once they get established in the numbers you are talking about. Females lay a couple hundred eggs at a time and these hatch and develop into sexually mature adults in about six weeks.
|Whiteflies on pomegranateNoticed they are on the bottom sides of the leaves.|
Conventional pesticides have not been very effective on whiteflies due to the development of resistance to applied pesticides. Now we rely on a more integrative approach to try to get a handle on controlling them.
This includes the use of oils and soaps when temperatures permit, yellow sticky boards that are renewed on a regular basis, reflective mulches such as aluminum foil, planting trap crops such as squash, hand picking heavily infected leaves early in the season, hand vacuuming, and others.
|Yellow sticky trap in greenhouse.|
You need to stay on top of this pest early in the season if you expect some control. Their numbers explode when it gets hot. When plants are still small, remove the bottom leaves close to the ground. These usually get infested first and they are impossible to spray on both top and bottom sides of the leaves which you must do.
Get on a regular spray program at their first sign, alternating with soaps and oils. Spray at least weekly both the underside and tops of the leaves. You will need a backpack sprayer if you have lots of plants or you might consider purchasing a fogger to apply pesticides.
|Solo backpack sprayer|
Foggers are quite effective but must be used when there is no wind. Use yellow sticky cards supported over the crop and replace it weekly. These can be used to help predict when to spray.
Trap crops that attract whiteflies, like squash, may also help. Squash plants strongly attract whiteflies and help to deter them from infesting other crops in the garden. Sometimes it may be easier to remove severely infested plants and replant.