How to Control Whiteflies on Tomato This Summer

Whiteflies on the bottom of pomegranate leaf

Q. I am new to gardening in the desert and am surprised at my success thus far!  That is, until the white flies came.  They showed up on the grapes and zucchini first, maybe in May or June.  Unfortunately, I didn't think they would become a problem. By August they had attacked everything! I pulled broccoli plants and found I needed a mask to keep from inhaling them! What can I do this season?

A. Whiteflies are a very tough to control once they get established in the numbers you are talking about. They are much easier to control if you’re diligent about controlling them when you first see them.

Females lay a couple hundred eggs at a time and these become adults that can lay more eggs in about six weeks. This means you can have exponential growth in their numbers if they are left undisturbed in six weeks.

Whiteflies, like so many garden pests, do not show themselves but remain hidden. Unless you stoop over and turn over leaves and look at their undersides, you will not know they are there until you see their telltale signs of plant damage. Signs of damage are yellowing and scorching of older leaves, sticky residue on upper leaf surfaces of lower leaves and ants.

Bottom leaves of sunflower yellowing and scorching due to past problems on the bottom side of the leaves.
Photo courtesy Viragrow.

Ants love the sticky residue that whiteflies and aphids produce. Ants climbing on plants in the garden or on fruit trees is a very good sign you have a developing pest problem.

Backpack sprayer suitable for vegetable and Orchard spraying

If you buy transplants to put the garden, spray the undersides of the leaves and the stems with insecticidal soap, neem horticultural oil. Once the transplants have been placed in the garden and they have grown a little bit, remove the bottom leaves of transplants that are within a couple inches of the soil.

These bottom leaves are perfect hiding and living quarters for many of the problem insects. They are so close to the soil surface they can’t be sprayed effectively.

Stay away from conventional garden insecticides unless this past really gets out of control. Whiteflies are resistant to many conventional pesticides and these traditional pesticides can knock out whitefly predators that help keep them under control.

Get yourself a decent compressed air garden sprayer such as Solo or Chapin and use soap and oil sprays in rotation with each other. Early in the season when it is still cool, check the undersides of the leaves and look for critters.

Weekly applications are probably enough during cool weather. When it starts to get warm, inspect the bottom sides of the leaves and spray twice a week. Make sure you spray the undersides of the leaves. That’s where these critters are!

Control ants that are getting into the garden. They are buddy buddy with aphids and whiteflies. Ants come from a nest in the ground. Follow their entourage back to the hole in the ground and treat around the hole with a bait that they can carry back to the nest. These are the most effective for ant control.

If you see bottom leaves that are starting to get yellow, pinch or clip them off. If they started to turn yellow they are contributing to the plant anymore. Look at the underside. There are probably critters feeding away. Removing these leaves, removes pest problems.