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Cabbage White Butterfly
Codling Moth
Herb Robert
Scot's Broom
Rogues Gallery
Weeds and Introduced Pests

No doubt about it, gardening has not always worked out the way people planned. Early on, growers realized that the region's gentle climate, abundant moisture, and good soil would be perfect for a wide variety of plants. They began planting gardens and landscapes filled with exotics. What they didn't know was that once some of these species were let loose in a pristine environment with no natural predators, the introduced plants and animals would set out to rule the world.

Today, some introduced plants are so common that they seem to be native. Which is part of their plan. It gives them enough time to spread. Here's how it works. An unsuspecting gardener gives a "volunteer" seedling a chance. Maybe the grower feels a little guilty about pulling out the pretty pink, or purple, or yellow "wild" flowers. Maybe he or she is curious, and just wants to see what the newcomer will grow up to be. Maybe the gardener is busy renovating the front border, and doesn't notice what's sprouting behind the garage. It doesn't really matter. Because in next to no time, the seedlings are everywhere and the gardener is starting to complain about pulling out the same stinking plant a dozen times. It happens all the time. Sometimes the weeds are merely nuisances, but make no mistake about it. The worst of these introduced pests are very serious problems. Noxious weeds can displace native ecosystems, poison people and animals, and ruin farms and ranches.

Unfortunately, there are many of these introduced weeds and pests from which to choose. I selected the ones below because their stories are well documented, and because they represent the various ways pests arrived in the region. There are, of course, many other serious weeds and pests.

Here are just a few of the big mistakes of gardeners past:

check Blackberry, Rubus laciniatus, R. procerus


Known in Portland
by 1850s - 1885

Certain blackberries, namely the woodland species called dewberries or trailing blackberries, Rubus ursinus, are native to the Pacific Northwest. Treasured for the delicately-flavored berries, these trailing blackberries grow at a civilized rate and behave admirably. If anything, berry-pickers would hope for more of them, since they taste heavenly. They are so good that plant breeders used them to develop the best domesticated blackberries.

It is the other blackberries, the ones that grow at an alarming rate, establish impenetrable thickets, and are nearly impossible to eradicate that are not from around these parts. There are two different kinds, and both are known offenders. Of the two, gardeners probably introduced the Evergreen blackberries, R. laciniatus, first. Historian Charles Henry Carey reports that these European imports "found a congenial habitat at the James Stephens place in the early [eighteen] fifties, on the Willamette, where East Portland was after laid out." Horticultural pioneer Dr. J. R. Cardwell, in a 1908 speech, claimed it was a Dr. Laurea who imported the plant from Hawaii.

Long before gardeners realized what was up with blackberries, they let loose another one. This time, it was the Himalaya blackberry, R. procerus. This berry took a circuitous route to the Northwest. Although it is native to Europe, an unidentified seed exchange in India listed it sometime in the late nineteenth-century. Horticultural luminary Luther Burbank, who had started working on blackberries in 1879, sent for seeds. When they sprouted, he recognized that this was no ordinary blackberry. He introduced it in 1885. In words that would prove entirely too true, Burbank's 1914 catalog proclaimed the Himalaya "not like other berries." It promised that Himalayas would produce buckets o' berries on vines that could grow 100 - 200 feet long in a single season. One wonders if anyone at the time asked an obvious question: "And that's a good thing?" Of course, nobody thought these berries would naturalize, an oversight for which gardeners will continue to pay in perpetuity.


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check European Cabbage White Butterfly, Pieris rapae

European Cabbage White Butterfly

Known in the region
since the 1890s.

Back when Northwest gardeners first began planting cabbages, they discovered that the region was a veritable Eden. All they had to do to produce picture-perfect cabbage was walk 2,000 miles on the Oregon Trail, stick a seed in reasonably good soil, and wait. OK, they also had to shoo away hungry deer and lug buckets of water to the plants in dry weather. But all in all, cabbage seed turned into heads of cabbage without a whole lot of strain. Cauliflower, brussel sprouts, kale, collards, and the other crucifers were almost as easy to grow.

Then sometime in the 1890s, trouble arrived. This time, it appeared as fat green larvae that metamorphosed into little white butterflies. Some thirty years earlier, these Cabbage White Butterflies had already taken hold in Quebec, their first North American foothold. By the 1880s they had followed Sherman's tactic, and marched through the south. At first, nobody paid much attention to them. After all, how much trouble could a few butterflies cause?

Unfortunately, every Northwest gardener now knows the answer. Leave virtually any broccoli-clan vegetable unguarded in the summer, and the cabbage-whites will use it to feed their babies. The eggs hatch into tiny green larvae that grow plump chewing big holes in the leaves. Masters at camouflage, the larvae are the same color as the leaves. When they snuggle up to a rib or vein, they look almost like part of the leaf. Bad infestations can chew young plants down to stubs. What was once an Eden for gardeners has turned instead into an Eden for cabbage butterflies.


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check Codling Moth, Cydia pomonella

codling moth larvae

Known in Oregon
and Washington
since the 1880s.

When Oregon Trail emigrants began planting fruit trees in the Willamette Valley in the 1840s and 1850s, they discovered that it was so easy to grow perfect apples that the region became known as the "Land of the Big Red Apple." The area had many things going for it. The land was rich. The weather was suitable. And perhaps most remarkably, there were no pests or diseases. No codling moths to drill worm-holes into the apples. No rosy apple aphids to suck the life out of the trees. No apple maggots, ermine moths, or any of the other evil-doers. Unlucky growers might be hit by a late frost, or try trees on a bad site, but most had healthy trees that produced perfect fruit without much fuss.

Unfortunately, those good old days are long gone. Codling moths arrived in Washington in the 1880s, probably catching a ride in an apple that nobody knew was infected. By then, it was a well-known pest elsewhere. Originally found in southeast Europe, codling moths arrived in the U.S. by the 1750s. A hundred years later, they'd made it west to Ohio, which was a big apple-growing area. From there, it was a short hop to Washington, especially if they caught a ride on the railroad. Once they arrived, there was plenty of habitat, since the region had lots of old, abandoned apple trees. There was virtually nothing to slow them down, until it was too late.


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check Dandelion, Taraxacum officinale


Known in Portland
in 1847.

Almost mild-mannered compared to the evil-doers on this list, dandelions are simply too good at growing. They fill up empty spots in lawns, flower beds, and even grow in sidewalk cracks. In many years, they are one of the first spring flowers, not that anybody appreciates their efforts. It was because of this early-spring growth that gardeners brought them to the Pacific Northwest. In the days when pioneers got through the winter on produce from their root cellars, the first spring greens were more than treat, they were a tonic. Many nineteenth-century gardeners thought dandelion greens were just what the doctor ordered. Science later confirmed that dandelions really do offer a jolt of vitamins and minerals.

In Seattle, it was Catherine Maynard, wife of Dr. David S. (Doc) Maynard, who reportedly introduced dandelions. In Oregon, Dr. Perry Prettyman gets the nod. He grew them on his donation claim near Mount Tabor near Portland in 1847. Others throughout the region undoubtedly grew them, too.


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check Herb Robert, Geranium robertianum

Herb Robert

Date of introduction

A Eurasian native imported as a medicinal used to stanch bleeding and later praised as a (get this!) "fragile" wildflower, Herb Robert is now occasionally, and more realistically called Stinking Bob. Like other true geraniums (summer bedding-plant geraniums are a whole different item) Herb Robert sets little flowers that mature into long, beaked seeds. Clustered together in the seedhead, they look like the bill of a crane. Separated into individuals, they twist into corkscrews, with the ability (on a better-behaved plant it could be called "nifty") to wind itself into the ground securing a good home for the seed.

Trouble is, Herb Robert knows no bounds. It forms thick stands, out-competing other plants. Since they sprout at any time, they seem to make several generations in a season. The good news is that they have shallow roots and are easy to pull. The bad news is that the leaves stink, they seed prolifically so new plants just keep popping up, and they are perfectly happy in just about any shaded spot. Where it escapes into woodlands, it chokes out native plants.


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check Ivy, Hedera helix

English Ivy

Date of introduction

A recent-inductee into the ranks of problem plants, ivy was long considered a perfectly acceptable landscape plant. Gardeners, who appreciated its ability to smother weeds, used it as a groundcover. They also planted it on fences and walls, counting on it to make a quick screen. Not quite all was well and good, however. Once the ivy took hold, gardeners had to pull the rampant vines out of trees and yank out ten-foot lengths of vine that threatened to smother perennials. In desperation, some took the weed eater to the groundcover, fighting back growth that threatened walks and everything else in its way.

Then things turned really ugly. Ivy went feral. Birds carried the seeds to parks and woodlands, where the seeds sprouted and took hold. Now, ivy chokes trees in parks and greenbelts. Hanging on by adventitious roots on the stems, ivy scrambles up trees and creates serious problems. For starters, the vines add considerable weight to the trees, making them more liable to wind-throw. The evergreen leaves, which shade the trunk, stop air circulation, and hold in moisture, changing the microclimate on the bark enough to shift the advantage to insects and diseases. The feral ivy was not just content to climb, it also sprawled. In woodlands, it was just as effective at smothering competitors as it is in gardens. Except that in forests, it was choking out all the native vegetation, leaving precious little habitat or food for wildlife.

Now, park and forest managers are trying to eradicate ivy. Meanwhile, the birds continue to spread it, eating the seeds that ripen each fall. And since birds sit in trees and probably prefer empty branches to those choked with ivy, they deposit seeds (with a little splat of fertilizer) where the plant has a good chance growing. Sooner than anyone would like, yet another ivy vine is climbing another tree. Insidious, isn't it?


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check Scotch Broom, Cytissus scoparius

Scotch Broom

Known in B.C.
by the 1850s.

Noted for its stinking, allergy-inducing flowers, Scotch broom may be the poster plant for invasive plants. For starters, it's a nitrogen-fixer. That basically means it makes its own fertilizer and will grow, quite nicely thank you, in the worst soil (think road cuts). There are lots of nitrogen-fixing pioneer plants that are garden-friendly, but broom has several other survival tricks up its genetic sleeve. Once the plants get big (and they will get big), you can't kill them by cutting off the tops. They just resprout. That means workers either have to dig them out, use weed killers, or resort to creative or desperate means. Grubbing out a few broom may not be a problem, but acres and acres of them? Besides, broom already thought of that. They produce mountains of seeds. The pods even explode when they are ripe, making sure the seeds spread even farther. These seeds are a botanical wonder. They are virtually indestructible. They last at least 80 years, waiting and waiting and waiting. What they're waiting for is for somebody or something to stir up the soil, like when an animal digs a hole or when a human grubs out a scotch broom. Then the seeds sprout and grow, and where there may have been one broom plant, there are a bunch of them.

Experts have at least two opinions about how and when Scotch broom first arrived in the Pacific Northwest. Some think it was a stow-away that arrived as a seed back in the days when shippers packed goods in straw instead of Styrofoam peanuts. Others think it may have been imported as an ornamental. Among those who thought this highly of broom was Captain Walter Colquhoun Grant. He planted it at his farm in Sooke, B.C. circa 1850.


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check Slug, Arion ater


Date of introduction

The Pacific Northwest has several native slugs. The biggest is the banana slug, Ariolimax columbianus. Some of them are huge, growing up to 10 inches long and weighing a remarkable one-quarter pound. Many hikers have seen banana slugs, which are often yellowish, tan, or brown but may be any shade from white to black. Since they (both hikers and banana slugs) hang out in the woods, staying as far away as possible from urban environments, the banana slug, like the other native slugs, are rarely a problem for gardeners.

In stark (and some would add raving) contrast, the introduced slugs are the bane of every gardener's existence. They include the ubiquitous European Black Slug, Arion ater, which is so different from native slugs that slug scientists put it in a different genus. The Black Slug is the one with the ridges and furrows on the back of its body. Like black bears, it comes in several colors, including brown. Another introduced slug, this one from Asia Minor and Europe, is the Great Gray Garden Slug, Limax maximus. Somehow even more revolting than the black slugs, this one has a smooth, gray body with darker stripes and spots. A couple other slimy species creep around at night outdoors. Another one lives in greenhouses and other warm, cozy spots. These imports were most likely stow-aways, arriving with plants.

If the slugs weren't bad enough, we also have snails. For those, we can thank an unnamed gourmet who arrived in gold rush San Francisco in the 1850s with a craving for escargot. He imported snails, some of whom apparently thought life on the lam was preferable to the alternative—a date with a pool of sizzling garlic butter. Not only did the escapees survive, they flourished. Eventually, they began moving north, hitching rides hidden in pots and plants.


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