New insect pestering people and plants in Willamette Valley

gardening image
Although the ash whitefly showed up in Oregon in 2014, its population increased exponentially this year. Photo by Robin Rosetta.
Last Updated: 
October 16, 2015

CORVALLIS – 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 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.

“It’s a sticky goo that can rain down on sidewalks and cars and be a real nuisance for people,” Rosetta said. “That will be what pushes people to ask about pesticides.”

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

“In one or two weeks it will look like you haven’t sprayed at all,” she said. “I don’t recommend spraying at this point. The plants like ash and ornamental pear where we’re seeing multiple life stages are all deciduous and the leaves will fall soon.”

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

In California, the population of ash whitefly declined by 99 percent within two years after the introduction of a parasitic wasp that is a natural predator, Rosetta said. She and officials at the Oregon Department of Agriculture hope the wasp will show up in Oregon on its own, or that they can get regulations in place in the next two to three years to import the insect.

“Bio-control is a pretty cool thing,” Rosetta said. “We have to be patient in the meantime. So sit tight.”

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.

For more information, refer to OSU’s Pacific Northwest Nursery IPM website.

 

Author: Kym Pokorny
Source: Robin Rosetta