YOUR GARDEN: Kym Pokorny

New insect pestering plants in WV

The ash whitefly is becoming quite noticeable for most of us.  It has a long list of plants it prefers.

Credit: robin.rosetta/ for Itemizer-Observer
The ash whitefly is becoming quite noticeable for most of us. It has a long list of plants it prefers.


Kym Pokorny

Clouds of small white-winged insects flying around homes, gardens and even parking lots up and down the Willamette Valley have the public more than a little annoyed.

“The ash whitefly, which was first detected last year, is becoming quite noticeable for most of us, particularly in the metro area, because they’re floating around in high numbers,” said Robin Rosetta, an entomologist with Oregon State University’s Extension Service.

“Many are familiar with whiteflies, but this is a new one. How impactful it will be is yet to be seen.”

So far, limited plant damage has been detected in Oregon, according to Rosetta, though the ash whitefly (Siphoninus phillyeae) can cause curled or stunted leaves and, in some cases, defoliation. The sap-sucking insect has a long list of plants it prefers. In California, where it showed up in 1988 and has largely disappeared due to an introduced parasitic wasp, there were about 40 host plants. In Oregon, they’ve been seen on Oregon ash, ornamental pear, hawthorn and flowering quince.

Other plants such as boxwood, barberry, rhododendrons and azaleas appear to attract the insect, but it doesn’t seem to be reproducing on these plants. More likely the whiteflies are moving on to them for winter protection.

Comments and questions about the aggravating insect are trending on social media and lighting up the hotlines of Extension’s Master Gardeners.

“There are a lot of calls,” said Margaret Bayne, administrative specialist for the Master Gardener program in the Portland metro area. “We’re telling people not to worry and to wait for OSU and the Oregon Department of Agriculture to monitor it and make recommendations.”

In addition to the large number of whiteflies floating around, people will begin to notice they secrete a substance similar to the honeydew produced by aphids.

Chemicals won’t have much of an effect, because the plants get re-infested so quickly.

Until more monitoring is done, recommendations are sparse. Using sticky traps may help, as well as raking up infested leaves.

Though other whiteflies are common in Oregon, including the ubiquitous greenhouse type, the juvenile ash whitefly is distinctive. The tiny eggs, which are laid on the underside of leaves, are pale yellow and hatch into nymphs that are almost translucent at first and then more opaque as they become covered in tufts of white wax, according to Rosetta. They develop into brown, egg-shaped young insects — called pupae — that can cause injury to the plant by sucking out its sap. 

As temperatures drop, the insects will become sluggish in their reproduction and activity and will largely disappear from sight with freezing weather. In spring, the whiteflies start multiplying more quickly and, by late summer and fall, numbers are high. How many are around next year depends on winter temperatures. A mild winter could mean even more next season.

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