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Tent caterpillars making an early comeback

Horticulturist: Larvae likely to infest south county this year


PHOTO COURTESY OF THE U.S. DEPARTMENT OF AGRICULTURE - Western tent caterpillars infest an aspen stand. The moth larvae are voracious feeders and can lay bare trees like alders and apples if not controlled.Every spring, thousands upon thousands of western tent caterpillars emerge from eggs laid on trees and bushes in Columbia County. The larvae will wreak havoc on certain species of trees, including some fruit trees.

This spring, according to a local expert, they’re starting early.

Chip Bubl, a horticulturist with the Oregon State University Extension Service in St. Helens, said tent caterpillars have been spotted weeks earlier than they typically hatch, and over a wider swath of Columbia County than usual.

“There are egg masses all over the place in Scappoose and St. Helens,” said Bubl. “And they have now started to emerge ... about a month earlier than they did last year.”

It is hard to ascertain the numbers and distribution of the tent caterpillar infestation until later in their life cycle, Bubl said. The caterpillars are notorious for the tentlike webs they construct in the branches of trees and shrubs to protect their colonies, which Bubl said make them difficult to control.

While Bubl said last summer that Columbia County saw one of its largest tent caterpillar populations in 20 years, he said the infestation was largely contained to about “a 10-mile radius” around Rainier.

“I think we’ll see a lot more this year in Scappoose and St. Helens,” he said.

Bubl attributed the early hatching of the larvae to the unseasonably warm weather so far this year.

“The mild winter was definitely the cause of bringing them out earlier,” he said.

The tent caterpillars are a menace to orchards and certain other trees.

“They like the rose family as well, which apples and pears are part of,” said Bubl. “They’re big-time on alders.”

Bubl is advising anyone with apple or pear trees to start looking now for tent caterpillars.

“The ones that are hatching are less than a half an inch at this point,” he said. “But they grow quickly as they start eating.”

To combat the tent caterpillars before they can grow and build their webs, Bubl recommends the use of the biological pesticide bacillus thuringiensis, or Bt. It is a natural bacteria that he said targets the larvae of butterflies and moths.

Drought-resistant plants’ suggested this year

Meanwhile, both Bubl and Maurice Horn, co-owner of Joy Creek Nursery near Scappoose, are suggesting gardeners take dry weather conditions into account.

Horn said the talk of a recent Pacific Horticulture Society conference he attended was that it could be an especially dry summer.

“They were encouraging people to look for more drought-resistant plants,” he said.

Because much of the rainfall this winter came in intense bursts, rather than being sustained over long periods of time as is typical, Bubl said groundwater supplies in Columbia County may be lower than usual.

“I’d expect to see some drier creeks in the summer, on this side, than we usually see,” Bubl said.

Horn recommends planting California lilac, cistus and other hardy plants, including grasses.

“Some forms of these plants are hardier than others and gardeners should do research to find the hardiest forms,” he added.

Western Oregon has what is known as a Mediterranean climate, due to its similarities to the climate zone surrounding the Mediterranean Sea.

“We’ve always known that we have to irrigate our vegetables,” Bubl said. “We don’t rely on summer rainfall to keep them going.”

For now, Bubl said the planting season for some crops has — like the tent caterpillars — gotten off to an early start due to the warm weather.

“There was a head start to the gardening that this weather is just fine for,” he said. “People are just waiting for it to warm up again before planting some of the more heat-demanding crops.”

Bubl is also an instructor in the Master Gardener program.

The Columbia County Master Gardeners are putting on their 20th annual Spring Garden Fair on Saturday, April 25, in the St. Helens High School commons. More than 35 varieties of tomato plants will be sold, and dozens of local vendors will offer other types of plants, vegetables and garden items.

The plant sale is set to run from 9 a.m. to 3 p.m. Admission and parking are free, although attendees are encouraged to carpool.

There will be a raffle, with tickets on sale for $1 from many Master Gardeners and at the Oregon State University Extension Service office in St. Helens.

For more information on the fair, visit http://www.columbiacountymastergardeners.org.

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