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Dennis Vieira

2020 Knotweed Season Recap

Weeds are always adapting and changing. Species crossbreed (with native or non-native species), become resistant to herbicides, and infest locations where we might not expect them. At the forefront of all these variations is the hardy woody knotweed species: Japanese knotweed (Polygonum cuspidatum), giant knotweed (P. sachalinense), and Bohemian knotweed (P. bohemicum).

If you thought those stubborn thistles were tricky to deal with, knotweed proves to be even more challenging and takes years to fully remove from a site. It’s so hardy that knotweed is known to grow in the craggy lava fields of its native range in Japan! However, in Japan, knotweed’s spread is limited due to poor soils, repeatedly being covered by volcanic ash, natural enemies that feed on it, and soil fungi that restrict its growth. Unfortunately, this is not the case here in Washington County. North American wildlife do not eat knotweed, allowing it to spread unhindered along streams and in disturbed areas. These dense stands easily outcompete native streamside vegetation, causing erosion and altering wildlife habitat. Not only is knotweed a pest in natural habitats, but it is also capable of growing through asphalt, affecting building foundations and roadways.

Grouped Knotweed
Knotweed sprout, flowers and leaves, and infestation along a creek. Photo credit: Tualatin SWCD.

Defending the Tualatin River watershed against this troublesome weed is no easy task. Invasive Species Technician Trevor Norman shares his experience of surveying for knotweed along Gales Creek:

“It’s muggy in the riparian undergrowth, almost like you’re walking through a jungle. The blackberry, reed canary grass, and willow are so thick you need a machete to cut your way to the creek. Every step you take requires a glance downward to scan for nutria holes. Stepping in one of these will end in a short field day. … A family of ducks float by you downstream, quacking loudly as if poking fun at your clumsy missteps. You look down at your iPad to figure out where you are, only to look up and find a black-tailed deer staring into your soul from a few yards away.

Moving slowly, you continue your journey downstream probing the undergrowth for the bamboo-like stems indicative of knotweed. It seems like you’ve slogged miles and miles; however, looking back, the truck is still in view. Every hundred feet you drop a data point cataloging the amount of knotweed you’ve found growing along the stream, and it’s a lot. You start noticing it, sometimes just a small sprout, sometimes 10-feet tall! There are no native species growing in these knotweed thickets … just an endless sprawl of tangled green stems erupting from clumps of last year’s dead growth.”

Knotweed has been actively managed along streams in the Tualatin River watershed by Clean Water Services since 2009, with Tualatin SWCD taking the lead in 2018. In 2009, a whopping 55 acres of knotweed was treated throughout the watershed! Having started the 2020 treatment season in early August, Tualatin SWCD’s Invasive Species Program has been working with local partners, landowners, and contractors to survey and treat knotweed infestations. In 2020, 1.78 acres were treated. This was a 97% reduction in known infestations across the watershed since 2009!

Map of Tualatin SWCD’s treatment area.
Map of Tualatin SWCD’s treatment area in 2020. Green squares represent treated knotweed infestations.

Often, knotweed takes three to four years to be completely eradicated from a site with proper management and monitoring techniques. They are known to sprout from small fragments. Digging, cutting, or improper herbicide use will only spread these plants by disturbing their robust network of underground roots and above-ground stems. Appropriate and carefully mixed herbicides applied in the late summer/early fall (before the first frost) are the only dependable way to treat knotweed.

If you have knotweed on your property, you can reach out to the Tualatin SWCD Invasive Species Program at Invasives@TualatinSWCD.org with a photo of the infestation. Once the infestation is confirmed, a certified herbicide applicator can survey and treat it for free.

It is only through our contractors’ dedication and hard work, property owners’ cooperation, and the community’s helpful observations that we have made huge progress in containing and managing this troublesome weed. Thank you for your continued vigilance and support!

Nature vs. Nature: Biological Controls in Conservation

Those of us who grew up watching Animal Planet are familiar with scenes of ferocious hunting and escape – a jarring portrayal of nature’s intense fight for survival. The interactions between mammalian predator and prey are widely seen; but this relationship occurs in all sizes, even among single-celled organisms. Predator and prey interactions have significant influence on the surrounding ecosystem. Land managers are learning how to leverage those interactions to reduce harmful pests and improve environmental health with biological controls.

Whether you’re a farmer, a forester, or a rancher, chances are there is a problematic organism affecting your property. This could be insects ravaging your crops, rodents preventing saplings from growing, or invasive weeds crowding out native vegetation. Traditional methods of controlling these nuisances include:

  • Chemical controls: herbicides, pesticides, horticultural soaps, minerals, and metals.
  • Mechanical & physical controls: trapping, mulching, manipulating habitats, and installing barriers.
  • Cultural controls: planting pest-resistant plant varieties, rotating crops, incorporating companion plants, and improving sanitation.

Biological controls are a broad group of methods that can look very different depending on the problem at hand.

Holey leaves are evidence of beetles munching away on this purple loosestrife plant.

Purple loosestrife is an invasive species that can take over entire wetlands. This reduces biodiversityBiodiversity The variety of species present. and harms wildlife who depend on native plants for survival. Birds are especially affected by the loss of nesting habitat. Large infestations also disturb ecosystems by slowing the flow of water and producing stagnant conditions.

Earlier this year, our Invasive Species Program strategically released black-margined loosestrife beetles and loosestrife root weevils at a site infested with purple loosestrife. The beetles and weevils are natural predators of purple loosestrife and also come from Europe and Asia. In its native habitat, the bugs control purple loosestrife by using it as a primary food source.

The beetles and their larvae reduce the plant’s ability to photosynthesize and reproduce by eating its leaves and flowers. The weevils attack purple loosestrife from underground. These insects and their larvae feed on the plant’s roots, which depletes its energy stores and can eventually kill it. Before using them as a biological control here in North America, the insects are carefully tested to ensure native plants aren’t harmed during the process.

Biological controls can involve the careful release of predatory insects.
Left – a black-margined loosestrife beetle. Right – a loosestrife root weevil.

Oftentimes, larger flying creatures are needed to control pests.

Birds of prey can act as living scarecrows across many types of landscapes. Unlike insect controls that feed on and kill weeds, releasing trained raptors represents a non-lethal solution to problem species.

In rural areas, high-value crops such as blueberries, cherries, and grapevines are frequently targeted by starlings, cedar waxwings, and blackbirds who enjoy these foods as much as people do. Falcons vigilantly guard properties to scare away small birds and prevent them from eating the ripening fruit. Peregrines and gyrfalcons are commonly used for these jobs, but prairie falcons and lanner falcons may also be deployed.

Flying raptors to scare away pest birds is a biological control method.
Left – a gyrfalcon. Photo credit: Elena Gaillard. Center – a Harris hawk. Photo credit: Peter Burian. Right – a large flock of starlings with raptor. Photo credit: Mostafa Meraji.

Harris hawks are the go-to defender in urbanized areas. These social and highly trainable birds are easily adapted to dense urban environments. What pests plague urban areas, you may ask? Crows! Large concentrations of crows can spread disease and cover plazas in unsightly excrement. Being larger than falcons, hawks effectively push thousands of roosting crows away from high-traffic areas toward green spaces. Guiding a murder of crows to vegetated places has the additional benefit of reducing water pollution. Animal waste is full of nutrients that can flow off hard surfaces – like roads – into waterways, causing destructive, and sometimes toxic, algal blooms. Planted areas will absorb excess nutrients, preventing them from disturbing aquatic ecosystems.

A raptor perch is a simple way to encourage birds of prey to occupy an area.

Protecting property from nuisance species by flying birds is a time-intensive practice that requires specialized skills. Sometimes, simply inviting wild birds of prey into an area can have similar benefits. At Tualatin SWCD, raptor perches are often installed at project sites that have been recently planted. Small mammals and rodents can prevent new forests from becoming established when they feed on the tender stems of young trees. A raptor perch is a simple and inexpensive way to reduce the risk of sapling loss by rodents. Unlike trained birds who scare away pests, wild raptors will help control pests by making them a food source. After all, everybody has to eat!

To see these methods in action, check out these videos!

Beetles Beat the Purple Loosestrife

Falcons: The Farm Defenders

Crow Abatement in Downtown Portland

Plant This, Not That: Native Alternatives to Pesky Ornamentals

When it comes to invasive plants, there is good news and bad news. The bad news is that many invasive plants are often planted intentionally as ornamentals. These plants can escape the confines of gardens, muscle their way into local ecosystems, crowd out native plants, and destroy wildlife habitat. Despite these problems, many of these troublemakers are widely available at local and mail-order nurseries. Just because you can buy a plant, doesn’t mean you should.

The good news: There are plenty of attractive native alternatives to choose from that aren’t harmful and increase habitat for native birds, wildlife, and pollinators. And now is a great time to make the swap! Fall is a great time to start planting, especially shrubs and trees. Below, you’ll find a list of pesky ornamentals and their delightful native alternatives.

PLANT Douglas spirea, NOT purple loosestrife

Image comparing Douglas spirea with pink flowers and purple loosestrife with purple flowers.
Photos: Douglas spirea (top right); purple loosestrife (bottom left)

Purple loosestrife’s (Lythrum salicaria) showy, upright clusters of purple flowers give it the nickname “the beautiful killer.” It is commonly planted as an ornamental species, but can quickly infest wetlands, marshes, and streams. Once mature, a single plant can produce up to 2.7 million tiny seeds annually, which spread by water, wind, wildlife, and humans. Infestations result in decreased bird habitat and can lead to erosion.

Rather than planting purple loosestrife, plant Douglas spirea.

The Pacific Northwest native Douglas spirea (Spiraea douglasii) has similar cone-shaped flower spikes, but they are usually pink rather than purple. Its flowers and dense growth also attract a variety of wildlife, including deer, butterflies, birds, and many other small animals. Douglas spirea blooms at a similar time as purple loosestrife, July through September.

PLANT red-flowering currant, NOT butterfly bush

Comparison of red-flowering currant with red flowers and butterfly brush with purple flowers
Photos: Red-flowering currant (top right); Butterfly bush (bottom left) – Kingsbrae Gardens.

You can’t blame gardeners for adoring butterfly bush (Buddleia davidii). This shrub’s purple-and-orange flowers are as dazzling to the human eye as they are to pollinators. Unfortunately, butterfly bush only benefits pollinators at one stage of their life cycle. It provides copious nectar for butterflies but it offers no food for native caterpillars. Its nectar is heavily concentrated and is essentially “junk food” to butterflies. Plus it does not always stay where we plant it. When it escapes into natural areas, it forms dense thickets, especially along riverbanks and gravel bars, which alter soil nutrients and crowd out native trees and shrubs.

In place of butterfly bush, try planting red-flowering currant.

Red-flowering currant (Ribes sanguineum) is one of the most common currant species found in gardens and landscapes. Its drooping clusters of light to deep pink flowers are one of the first things to bloom in the Pacific Northwest, corresponding with the time mason bees are hatching from their cocoons and searching for energy-packed nectar.

PLANT wild ginger, NOT English ivy

Comparison of Wild ginger with light green leaves and a purple flower and English ivy with dark green leaves
Photos: wild ginger (top right) – Mount Rainer NPS; English ivy (bottom left)

English ivy (Hedera helix) is a plant that many people seem to love, but it’s really a plant that people should hate! While it is useful in landscaping as an evergreenEvergreen Plants that maintain their leaves all year long. groundcover, its ability to escape gardens and dominate habitats makes it sinister in parks, natural areas, and forestlands. Once it has escaped, English ivy quickly outcompetes native plants for light, nutrients, soil, and space, creating “ivy deserts” that are defunct of wildlife habitat. Ivy is particularly harmful for trees. When left unaddressed, ivy can engulf entire trees and prevent their ability to photosynthesize.

Instead of planting English ivy, plant wild ginger.

Wild ginger (Asarum caudatum) is a fast-growing ground cover with nice, big heart-shaped leaves. The plant is deer-resistant and an important source of food for local pollinators. Wild ginger grows in shade and greens early in the spring through late fall. Plant it once and it’ll grow like crazy! If you are planting in a sunnier location, we suggest planting a variety of native strawberry (Fragaria species), which is better suited to direct light.

PLANT tall Oregon grape, NOT English holly

Comparison of Oregon grape with shiny green leaves and yellow flowers and English holly with siney green leaves and green berries.
Photos: tall Oregon grape (top right); English holly (bottom left).

For many people, the glossy, dark green leaves and bright red berries of English holly (Ilex aquifolium) are synonymous with the holiday season. While popular, this plant is not native to Oregon. In fact, English holly can quickly spread when planted in our region, shading out native plants and degrading our natural habitats. Additionally, its spiny leaves and berries can be toxic to humans, dogs, and cats.

Rather than planting non-native English holly, try planting tall Oregon grape.

Tall Oregon grape (Mahonia aquifolium) has similar-looking leaves and can share the same stature as English holly. This leads to observers mistaking the two species. Oregon grape is a Pacific Northwest native and can be distinguished from holly by its bright yellow flowers, which attract bees, hummingbirds, and other pollinators to the garden. Holly, on the other hand, does not typically have flowers. Another way to tell these two plants apart is by looking closely at their leaves. Holly’s leaves are alternate along the stem, whereas Oregon grape’s leaves are opposite.

Laminated Root Rot: The Inconspicuous Tree Disease

Fungi play a major role in forest ecology.

Similar to bacteria and certain critters (like worms, snails, beetles, and termites), fungi facilitate nutrient cyclingNutrient Cycling The transformation of a chemical as it moves through a system. through decompositionDecomposition The process of organic matter breaking down into smaller parts.. Fungi break down dead and dying tissue into nutrients, including proteins and minerals. These nutrients then support living, growing plants and animals. Decomposition is a slow process that can take many years, but even trees that haven’t completely returned to the soil provide important benefits. Standing dead trees are important habitat for cavity-nesting birds and mammals, and wildlife that forage on insects. When a tree loses its leaves and branches, it creates a gap in the forest that can spark a series of forest activity. More space and more sunlight allows other species of trees and shrubs to grow – increasing overall forest diversity.

There are several types of fungi-caused root disease. Laminated root rot is one of the predominant root diseases in Western Oregon.

While hardwoods are immune to the pathogen, Phellinus weirii can be detrimental to stands of Douglas fir, grand fir, white fir, and mountain hemlock. Root rot hinders trees’ ability to take up water and essential nutrients. Once affected, trees are more susceptible to other health problems, like bark beetles. Trees of all sizes and ages can be infected by laminated root rot, but because early mortality is scattered among young, small trees, the disease usually isn’t obvious until the stand reaches maturity. Once symptoms are visible, the infection has already spread considerably, making it difficult to bring under control. For these reasons, forest owners must be vigilant against this inconspicuous tree disease.

LRD Healthy VS Diseased Root Pieces
The piece of root on the left is healthy, while the piece of root on the right is decaying from laminated root rot.

Managing laminated root rot requires an understanding of how Phellinus weirii spreads and survives.

Most infections begin when the roots of young stands come in contact with the fungus that is living in decaying wood from past generations of trees. The rate of spread through a stand can be quite rapid, averaging about 34 cm per year (over 2 feet), but symptoms in the forest crown may not be noticeable until 50% or more of the root system has been destroyed.

Because the disease spreads from infected stumps to the roots of healthy seedlings or trees, the key to managing laminated root rot is to catch it early and isolate the fungal network underground. Excavating infected stumps and roots can help ensure new generations of trees don’t become infected. But this method can be expensive, and fungi can linger in the soil on broken roots. A better way to manage this disease is to remove all visibly infected trees in the disease pocket, remove a 50- to 100-foot buffer of healthy trees around the pocket, and interplant disease-tolerant or immune tree species. This approach won’t remove Phellinus weirii from the site, but it will reduce the effects of the disease upon the stand as the fungi cannot spread as effectively on roots of resistant or tolerant tree species. Hardwoods like big leaf maple, Oregon white oak, and Oregon ash are immune to the disease, while Western red cedar and ponderosa pine are resistant.

To learn more about laminated root rot and prevention, check out these resources:

Washington State Academy Of Sciences

The Woodland Workbook

Forest Disease Mangement Notes

Pacific Northwest Pest Management Handbooks

The Benefits of Fall Planting

If you’re ready to put your garden tools away and leave planting until spring, think again! Many folks are surprised to learn that fall is a great time to start planting, but it’s true! Cool temperatures, reliable rainfall, and short, bright days help plants make an easy transition to your garden. Instead of thinking of fall as the end of the gardening season, think of it as the beginning of the next one!

Here are a few reasons why fall planting is so beneficial:

Cool Air, Warm Soil

With cooler air temperatures during the day, plants get a welcomed break from summer heat stress. Likewise, soil temperatures stay warm from months of summer sun. Cool air temperatures plus warm soil is the perfect combination for fall planting!

Cool air and warm soil conditions cause plants to focus their energy underground, while their above-ground growth begins to slow. Protected roots will continue to grow until the ground freezes. This head start on root development results in strong, robust plant growth come spring. It’s best to plant or transplant plants about six weeks before the ground freezes. In Washington County, that normally happens in mid to late November – so September is prime for planting.

Less Watering

Consistent rainfall typically arrives with fall’s cool temperatures. Planting during soggy, unpredictable springs can be difficult and may even be harmful to your garden’s soil structure. Working wet soil will pack soil particles tightly, leaving less room for water and preventing roots from moving through the soil. But planting during the fall, when soil tends to be drier and more loosely packed, is much easier and more beneficial to your soil. Consistent precipitation also means less watering for you, so you can fit in one last summer BBQ before the weather turns! If rainfall comes up short, make sure to keep new plants watered until the ground freezes.

Fewer Weeds and Pests

Many garden weeds and pests are warm-season nuisances that slow down or disappear come fall. Actively growing weeds compete for water, light, and nutrients, contending with new plantings for every ray of sunshine and each drop of rain. By planting in the fall, new plants get a head start without having to compete with obnoxious weeds. Fall weather also brings a drop in insect activity. That’s a plus for gardens and gardeners so you can plant in peace – without having to swat mosquitoes or worry about your new plants getting devoured.

As always, we recommend planting native plants no matter the planting season. Where can you find native plants? Native plant sales of course!

Each spring and fall, many nurseries and conservation organizations hold native plant sales encouraging gardeners to incorporate native plants into their gardens. Proceeds from these sales help support community organizations. Our friends at the Backyard Habitat Certification Program have a list of plant sales happening around our region.

Keep Your Eyes Sharp for Puncturevine!

Many of life’s lessons teach us that the inconspicuous things are those that you need to keep an eye out for. In more arid regions there is a plant that everyone knows because they have probably stepped on it or had a tire popped by it : puncturevine. Now, this troublesome pest has been popping up in our area. If we don’t act quickly, puncturevine will become increasingly common and start sprouting along our sidewalks or yards.

What Does It Look Like?

Weeds are often described as pesky, but a better word for this one is NASTY. Puncturevine (Tribulus terrestris) is an annual herb that grows as a groundcover with small, opposite, compoundCompound A leaf consisting of several distinct leaflets joined to a single stem. leaflets that are covered in tiny hairs. New sprouts begin to emerge soon after the first spring rains, with flowers quickly developing within two to five weeks. Its flowers are bright to pale yellow and have five petals that close during the evening. Once mature, it grows burrs that comprise of four to five seed pods that have two large sharp spines each. The burrs hide close to the ground out of sight until you ride over them or decide to skip putting on your shoes to grab the mail.

Why Should We Control Puncturevine?

To make matters worse, puncturevine is toxic to livestock, particularly sheep and cattle. When livestock consume it in large amounts, they can succumb to nitrate poisoning that can cause blindness, paralysis, and even death. Puncturevine’s sharp burrs injure livestock’s hooves, skin, and mouths when they graze in infested areas, causing serious injuries. Pets also get the burrs caught in their paws, causing distress or injury. Unfortunately, puncturevine tends to invade agricultural lands such as orchards or hay fields, contaminating agricultural products with its spiny burrs.

What Should I Do If I Find Puncturevine?

Puncturevine is well-established in Eastern Oregon. It has been documented west of the Cascades, including in the Portland metro and adjacent areas. However, it is not as widespread in our region as other spiny invasive species such as blackberry or English holly. There is still a chance to keep this weed from claiming bicycle or ATV tires throughout the Tualatin River watershed. We are asking anyone who spots puncturevine to please report it to the Oregon Invasive Species Hotline with a photo and location of the infestation. Once we have confirmed the identification, a trained weed expert can come out to control the puncturevine for free.

Your observations could help keep this painful nuisance from overrunning our farms, natural areas, and parks – or from ruining your day with a popped ATV or bike tire!