Emerald Ash Borer

What we can do in response

The discovery of the emerald ash borer in Oregon has many people rightfully worried about the fate of ash trees in our region. The Emerald Ash Borer, or EAB, is an invasive wood boring beetle that feeds on ash trees. There are thousands of wood boring beetles in the world, and most cause no problems at all, but EAB isn’t native to North America, where it has fewer natural predators and the ash trees have no natural defenses.

EAB was first discovered on the North American continent in Southeastern Michigan in 2002, likely brought in with wood packing material. Since its introduction, it has caused catastrophic tree deaths and slowly spread across the continent.

EAB has likely already been in our area for a few years; the amount of time that it takes for a healthy ash tree to die from EAB is 3-5 years, that is why we are seeing some of the first trees in active decline right now.

Ash trees make up 5% of Portland’s street tree canopy (1 in every 20 trees!) and there are 9,000 ash trees on streets and in parks of Eugene (with many more that haven’t been inventoried). In certain areas the absence of ash will be more stark than others. We will particularly notice ash trees dying in large numbers in certain natural areas (the Oregon Ash, Fraxinus latifolia) and in parking lots, where they are a popular landscaping tree. It is important to know that preemptively removing ash trees in large numbers will not stop EAB. The ash trees we have, as long as we have them, provide tremendous benefits to us and our environments

In response to the EAB’s arrival, some Friends of Trees staff members are taking trainings, doing research, and formulating our best response to the EAB presence in our community.

“We have a huge community of people with tree knowledge,” says Green Space Specialist Harrison Layer. “If we can accurately take notice of trees in distress, we can make a difference.”

What we can do:

  • Learn how to identify an ash tree.
  • Destroy ash trees that have died from infestation.
  • Give insecticide treatment to ash trees of distinction, important members of our community.
  • Plant a diversity of species in their place.
  • Find ash trees who do not succumb and appear resistant to Emerald Ash Borer, scientists need to know about these survivors with important genes!

“It gives me hope to think about finding trees that are resistant to EAB,” Harrison says. “It helps me imagine a future where we still have ash trees.” The USFS Dorena Genetic Resource Center south of Eugene has successfully bred disease resistance to blister rust in sugar and western white pines, and to Phytophthora lateralis for Port-Orford-cedar, giving hope for resistant strains of OR ash.

There are several natural predators of EAB, and EAB will likely cause a boom in native wildlife that eats EAB. Many birds, especially woodpeckers eat EAB larvae and pupae, and some native wasps have been documented to eat EAB larvae. Woodpecker activity on an ash is a hint that it could be infested with EAB. Sometimes blonde patches of sloughed off bark can be seen on the tree from woodpeckers, because EAB makes eating trails in the sapwood right under the bark surface.

EAB doesn’t infest ash trees less than 1-inch in diameter, meaning the ash we have planted in the Green Space Program the past couple planting seasons are immune for now.

Ash trees in decline will often feature defoliation from the top of the tree, epicormic growths (suckers from base), and have ‘D-shaped holes’ in their trunks. It is important to remember that the actual beetle can only be seen during its ‘flight period’ which is roughly between June 1st and August 30th.

“There are many green beetles that are native to Oregon,” Harrison says. “So it’s really important to correctly identify the EAB Beetle.”

While an EAB has the ability to travel up to 50 miles in flight, it doesn’t usually travel more than 10 miles in a year; furthermore, they typically settle on the next ash tree that they find, which is often much less than 10 miles away. It will take decades before EAB run out of food in our region.

Again, it is important to know that removing ash trees in large numbers will not stop EAB. The ash trees can still provide tremendous benefits as long as we have them. We will need to monitor the situation as long as we can to learn, adapt, and hopefully one day recover.

Other resources:

Leaflet – Watching the Seasons Change

You’re not the only one who’s noticing that the days are getting shorter. Our trees are noticing, too, and they’re taking it as a sign that the growing season is over. How do they notice? A hormone response is triggered by the shorter daylight hours, the angle of the sun, the cooler temps. This past month, you may have noticed a spring-like flush of herbaceous growth on your trees—one final push before autumn. That new growth will harden into woody material tough enough to survive our first frost in November.

Leaves on some deciduous trees will start changing color, a welcome sign of the cooler seasons after an especially hot summer. In a process called abscission, trees reabsorb the nutrients stored in the leaves before detaching and shedding them. Chlorophyll, which gives leaves their green color, is one of the first things to be absorbed, which is why we see them change color. But fallen leaves still have plenty of nutrients, which is why we encourage you to leave the leaves. Trees are putting those leaves there on purpose, to enrich the soil for their roots.

Most deciduous trees shed leaves in the fall. Some don’t though! Scarlet oaks, swamp white oaks, and many evergreens shed leaves in the spring as new growth emerges

For now, the best thing we can do is watch the weather, just like our trees are. Continue your watering regime until we’ve had one inch of rain in a week. After that, we’ll be out of the dry season and beyond the growing season when trees actively expand their canopies as they photosynthesize. And it happens to coincide with the timing for our trees to transition into winter dormancy, when their sap returns to their roots.

Roots can grow year round in the right conditions—moisture, air, and temperature—which is why we plant when we do, so trees can focus on establishing their roots. To help keep those conditions right for your young tree, make sure you replenish your mulch in the next couple months. One inch of mulch is a windbreaker, three inches is like a down jacket – and we want that year round, protecting against temperature extremes. Tree roots can grow 365 days a year as long as they have some moisture and a moderate soil temperature, both things that mulch provide.

This time of transition can be really exciting. It’s always remarkable to feel like summer is barely over, but by Halloween, which is now right around the corner, most of our trees will be dormant. As the seasons change, so do the needs of our young trees. So watch the weather, and stay tuned to Treemail for best practices for each season!

Leaflet: Aphids

Aphids are everywhere, but don’t worry!

We’ve been getting a few inquiries about aphids this summer. And with the arrival of the emerald ash borer (a devastating issue we’ll keep you posted on), we have plenty of reasons to keep an eye out for pests. In the case of aphids, however, we don’t need to fret about them on our trees like we do in our veggie gardens.

In almost all instances, you don’t need to take any action—the tree can take care of itself. Aphids will only make a noticeable impact if the tree is still working to establish itself, or is somehow otherwise weakened. We often see them on Oregon ash, like the one pictured. If some wilting or crinkled leaves have you worried, here are some action steps you can take. Some folks might want to go straight to spraying, but pesticides really aren’t necessary to deal with aphids.

If you have more than just a few aphids on your leaves, the first thing to try is to just rinse them off with water. A good hose down will take care of a minor infestation. If that doesn’t quite do the trick, you can spray with soapy water. A treatment like this just once or twice a year will be enough.

If you see any ladybugs alongside the aphids, that’s great! Ladybugs will eat the aphids, and their larvae will really go to town feasting on them.

Aphids are everywhere—there are even tiny ones floating in the air we breathe. Some trees, like littleleaf linden, will have so many aphids that you may feel a mist of aphid “honeydew” when you walk underneath. You guessed it, that’s aphid poop. Just think of it as a nice reminder that trees are part of a larger ecosystem of living things.

Leaflet: Summer Glory

Shop now, plant later

Now is when trees are in their full glory. You can see it, smell it, and feel it whenever you walk around the neighborhood. It’s not a good time to plant trees—we’ll wait until our planting season, October-April—but now is the time to be thinking about what tree you might want to plant. Look for the species on a Friends of Trees tag. Consider how big a tree gets when it’s mature.

“When we call you later this year to see what tree you want, you won’t be able to look around and see what a tree looks like in the middle of summer,” says Neighborhood Trees Senior Specialist Andrew Land. “Summer is an outstanding time to look around.”

Beyond finding a tree whose glory really speaks to you, now is also a great time to think critically about the conditions where a particular tree can succeed. A core aspect of the Friends of Trees ethos is right tree, right place. We want every tree to survive and thrive.

If you see a tree you really like and think, maybe I want one of those, observe the place that it’s in. Consider the conditions: sunlight, moisture, competition, space. Compare those to the conditions in your own yard where you might want a tree.

When we talk about a tree getting full sun, we’re really only talking about the growing season from mid-April through September. The sun exposure in your yard changes considerably from season to season. Now is the time to study how much sun your new tree would get next summer.

“Thinking ahead is how we set up a tree and its steward—you—for success,” Andrew says.

We always invite you to connect with staff about tree selection. And we encourage you to keep an open mind to something new and different. Don’t be afraid of big trees. Consider trees that will be more resilient to climate change. Glory is subjective, and there are so many factors beyond appearance.

“Take the Hardy Rubber Tree, for example,” Andrew says. “It’s nondescript. You wouldn’t necessarily call it pretty. But it’s the best air filter of all the trees.”

Or take the Amur Maackia. It’s not known for its spring flower or its fall color, but it casts a beautiful dappled shade and does really well in the urban environment. When it comes down to it, survivability is the biggest priority.

“Think of all the benefits that a tree provides to people and community,” Andrew says. “Those benefits expand exponentially every year that a tree survives, which is why we want every tree to last as long as possible.”

Leaflet

Restoring the Balance

Today, we’re asking you to put yourself in a tree’s shoes–or roots. Planting day is so exciting for volunteers. We get to hang out with our neighbors, get our hands dirty, and feel good about getting trees in the ground. But planting day is the most stressful day of a tree’s life.

When we plant a tree, we have to cut some of its roots. Container-grown trees need to have their roots cut to prevent them from circling in on themselves, even after they’re put in the ground. Ball and burlap trees are grown in the ground, but they also get their roots cut when they are put into that ball to be moved to their final location.

Trees are all about balance. Balance between canopy, where the tree can feed on sunlight and perform photosynthesis, and roots, which pull nutrients from the soil and provide the tree its needed strength and stability. For a newly planted tree, this time of year is all about restoring that balance and getting the roots and the shoots established.

Trees are like icebergs—there’s a lot more going on beneath the surface than we realize. Being able to understand what’s going on underground for our trees helps us better care for them, especially when it comes to watering.

We’ve mentioned watering plenty, but it’s so important that we can’t really talk about it too much. We have had an incredibly wet spring, which is great for the trees! As stewards, we’ve been able to keep our foot off the gas—we haven’t really had to worry about getting out our hose or watering bucket all that much.

But at some point the rain becomes intermittent and shallow enough that it doesn’t reach the tree roots. Watering trees is very different from watering grass, which benefits from frequent and shallow watering. One of the most common watering mistakes is watering your tree like you would your grass, for just a few minutes every day. For trees, we want deep and infrequent. In the summer, a thorough watering once a week is a perfect schedule (see details here).

When you water your tree, imagine what’s going on underground. We want to water the tips of the roots as they spread out. Another common watering mistake is when folks just point their hose at the base of the trunk and water there. You want to simulate a rain storm for your tree, watering all sides, and several feet away from the trunk so that you get the tips of the roots.

Overwatering is rare, but you still want to avoid it. Again, it helps to picture what’s going on beneath the surface. Perfect soil is about 50% air and water pockets. Too much water can flatten those pockets and there’s no air. You’re essentially drowning your roots. Beyond that, too wet soil threatens the stability of the tree. When a tree fails because it’s thrown by the wind, it’s usually because the soil is too wet.

This time of year, we are spectacularly rewarded for our care for our trees. Bud break, flowering, leafing out—it’s a rejuvenating thing to see each spring.

If you’re thinking about getting a new tree for your yard next year, now is a good time to consider which species you might want! What trees are catching your eye? What looks like it might be right at home in your yard. Take note now, and next year, we can get you what you’re looking for!