OSU helps defend America's favorite flower against voracious midge

March 10, 2005

AURORA - A pinhead-size maggot with an appetite for roses is attacking Portland, Ore., the Rose City.

Faced with losing the city's emblematic flower to the ravenous rose midge – and seeking to minimize insecticide use – Portland city officials have sought help from pest management specialists with the Oregon State University Extension Service.

Portland loves roses and celebrates them in its annual Rose Festival, in the name of its sports arena (the Rose Garden) and in its International Rose Test Garden. But two years ago, tiny rose midges seemed to be sucking the life out of Portland's roses. The midge had been a problem for several years in Portland's Rose Test Garden, where 10,000 rose bushes are on public display. But in 2003, the garden lost half of its rose blossoms by mid-summer and three-quarters of its blossoms had shriveled by the end of the season.

Last year, Portland Parks and Recreation Department workers sprayed insecticides to keep the midge at bay. This year, OSU Extension horticulturist Robin Rosetta is working with the department to find a way to control rose midges more effectively with less frequent and possibly less toxic methods, consistent with Portland's nationally-recognized program of integrated pest management in city parks.

"Our hope is that we can reduce our reliance on pesticides by discovering the very best integrated pest management approach," said John Reed, the IPM manager for Portland Parks and Recreation. "We're looking for the best way to target the pest and minimize the need for pesticide applications."

Roses are one of the nation's top ornamental plants, so the rose midge could have significant economic impact beyond the Rose City, according to Rosetta. In the last few years, there has been an increase in the distribution and occurrence of the rose midge across the United States.

The millimeter-long white maggot is the larvae of an even smaller fly, a native insect of North America. It feeds on the soft growing tips of roses, and although it does not kill the bush, it leaves rose buds and stem tips withered, black or distorted.

The rose midge was first described as a pest to ornamental roses in New Jersey more than 100 years ago, when the most effective control was a tobacco mulch made from cigar-factory leftovers.

Chemical pesticides developed since the 1950s were even more effective, but they killed good bugs as well as bad bugs and raised concerns about public health. Those chemical pesticides have since been banned or restricted, and Portland city park officials are committed to using controls that minimize risks to people and the environment.

So Rosetta's challenge is to find controls that are specific to the rose midge, effective and with minimum environmental side effects.

"When it comes to controlling pests, you've got to get 'em while they're down," Rosetta said with a laugh. "You identify the most vulnerable phase in the pest's lifecycle and find ways to attack it at that point."

With the rose midge, the vulnerable phase occurs early in the season, when the over-wintered larvae are emerging from the soil. Later in the season, when all lifecycle phases are present, it's more difficult to precisely target a control treatment.

This winter, Rosetta planted her own rose test garden, 88 rose bushes at OSU's North Willamette Research and Extension Center in Aurora, where she is able to test various methods of integrated pest management in tightly controlled conditions.

She's replaced the old arsenal of banned pesticides with a wide array of treatments, including biological methods using beneficial bugs and fungus to counteract the midge; and chemical methods including pesticides called neonicotinyls, which are similar to the natural pesticide found in tobacco and the old-time mulch from cigar factories.

"It's complicated working on rose pests because there are so many things that can infect roses, making evaluation of our research more difficult," Rosetta said.

So far the rose midge is predominantly a problem in large display gardens, where it seems to spread to new sites through infested soil or movement of the adult midges. It is not yet a large problem in nurseries or backyard gardens, according to Rosetta. She and her OSU colleagues are working with researchers in Ohio, New York and British Columbia to halt the outbreak of rose midges in the Rose City and elsewhere and to nip this pest in the bud.

For more information and photos of the rose midge, go to Rosetta's OSU webpage at: http://oregonstate.edu/Dept/nurspest/rose_midge.htm

Author: Peg Herring
Source: Robin Rosetta