Whiteflies Won’t Go Away; Prune Weeping Cherry | Print |  E-mail
Thursday, 14 February 2013 13:11

By Buzz Bertolero

The Dirt Gardener

Q: I had a severe infestation of whiteflies last year. What can I spray now to prevent them from returning?

A: Whitefly is a pest problem that plagues vegetable gardens and evergreen ornamentals such as escallonias, pyracantha and fuchsias during the summer months. It’s beneficial to make one application of an oil spray to evergreen shrubs. It will clean up any over-wintering whiteflies that are on the foliage.

Bonide Four Season Oil and Monterey Horticultural Oil are two of several brands available. They’re both environmentally responsible insecticides around pets and people. The oil suffocates the insects. In a vegetable garden, they are usually not a problem with cool-season crops such as cabbage, cauliflower, lettuce and others; hence, spraying now provides no benefits.

Whiteflies are a serious problem on tomatoes, squash, peppers, eggplant, melons and pumpkins. The population starts off slowly and they build up rapidly when the temperatures warm up.

When temperatures are over 80°F, whiteflies can complete a generation in as little as 18 days.

The first thing you need to do in managing this pest is to be diligent in looking for them early on. In April, I’d place several yellow sticky traps in the area of where they were a problem last year. The adults are attracted to the color yellow and are then caught when they land in the clear, sticky resin. The traps will help monitor the activity and level of adult whiteflies in your garden.

Once I see whiteflies in the traps, I start looking at the underside of the leaves of the host plants. Early on, you can just pick the infected leaves off and discard them.

When the population starts to build up, spray with an oil product. The best time of the day to spray is in the early evening just before the sun sets. Your goal is to keep the population at a manageable level, so you need be pro-active all summer long.

The biggest mistake made is waiting to do something. By mid-summer, when the population is huge, your only alternative is to dig the vegetable plants up and discard them.

Q: I have a weeping cherry in a container. How far back should I cut the branches? Should this be done now or after it has flowered in the spring?

A: Flowering trees are usually pruned after they finish flowering. You can certainly prune it now, but you only reduce the color show you waited all year for.

How far back you prune the branches on a flowering cherry is a judgment call on your part. It could be several inches or feet.

The bottom of the branches can be uniform or you can stagger the lengths; it depends on how the plant is being viewed.

I would remove any dead wood and you might thin out branches that are very close to one another.

Another thing I suggest is to take some before-and-after pictures with your smartphone or digital camera. It’s a valuable resource next year when it comes time to prune again.

Buzz Bertolero is Executive Vice President of Navlet’s Garden Centers and a California Certified Nursery Professional. His web address is www.dirgardener.com and you can send questions by email to This e-mail address is being protected from spambots. You need JavaScript enabled to view it or to 360 Civic Drive, Ste. “D,” Pleasant Hill, CA 94523, and on Facebook at Facebook.com/Buzz-Bertolero.



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