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.
- The Oregon Invasive Species Hotline is a great resource for people to report suspected ash trees suffering from EAB.
- Oregon Department of Agriculture – EAB Resources
- The Emerald Ash Borer – Untamed Science
- Oregon State University – Oregon Forest Pest Detector Training
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.
Determining Your Tree’s Watering Needs
We’ve had a wet April, which means your trees are getting plenty of water! But the transition from spring to summer can be a tricky time to determine when to water your tree. Come this time of year, we recommend watering once a week when the weekly rainfall is less than one inch. But you might find yourself wondering, “when did it rain last?” (You can check here!)
Too much watering is the most common mistake, but consistent watering is crucial to getting these young trees established. A good way to know if your tree needs water is to check the soil. Stick a garden trowel or even a pencil 2-3 inches into the soil. If the soil at that depth is dry to the touch, then your tree is ready to be watered.
Once the dry season settles in, watering once a week is a good schedule (pick a day to water and keep it up!). Deep watering is best for these newly planted trees. Give 10-15 gallons at a time. Water slowly so that moisture soaks deeply into the soil and water doesn’t run away from the root zone. Mulching is a great way to hold water in the soil for your new trees.
Either a gator bag, hose on a gentle trickle for maybe 20 minutes, or a 5-gallon bucket with three 1/8″ holes drilled on the side at the bottom and filled 2-3 times consecutively works great. It’s a good practice to move the bucket around the tree each time you fill it to ensure that the whole root system gets water. Think of it this way: we’re trying to simulate a rain storm, during which all parts of the root system will get water at about the same time and rate.
It’s important to note that dry and hot are two different things. In late spring and early summer, we may get some seemingly perfect weather, and you don’t think to water your tree because it isn’t hot outside. But regardless of temperature, a dry spell is characterized as 2-3 weeks without significant rainfall. It might not be hot out, but your tree still needs a drink!
If the temperature gets over 90 degrees, bump your watering schedule up to twice a week. If we see another heat “event” coming, a good, deep soak beforehand can help the tree survive.
Spring has Sprung – What that means for your trees
Trees are breaking dormancy, but that doesn’t look the same for every species. Some are early risers, and some sleep in. A bunch of factors go into it, including species, daylight, and temperature. Here are some things you can do to take care of your trees this time of year.
It’s a great time to refresh mulch as needed. The objective is to mulch the tips of the roots as they grow outward from the base of the trunk. They will grow into soil that’s moderate in temperature and contains moisture, factors that mulch will provide. Because the roots are growing outward, when you mulch trees in their second year in the ground, aim for more of a 4-5′ diameter ring of mulch, still 3” thick, about a foot from the base of the trunk.
You may have noticed that some trees hold their leaves through winter. They’re called marcescent leaves, and they are a sign of last season’s growth. You’ll see them on native oaks like Oregon white oak (Quercus garryana) and scarlet oaks (Quercus coccinea). Come spring time’s flush, these leaves will be shed to make room for new growth. You can use these leaves as mulch!
Go easy on the pruning
It’s best to go easy with regard to pruning during “bud break.” This is when sap is rising up the tree, after having dropped to the roots in the fall. As the sap is rising, some trees (maples, for example) will “bleed” if pruned as sap is rising. It’s not harmful to the tree—that’s where maple syrup comes from, after all—but it can be disconcerting to see.
It’s almost time to start weekly watering for newly planted trees. “Deep and infrequent” is the recipe for success. Starting mid-April, 15 gallons all at once, once a week is ideal. Either a gator bag, hose on a gentle trickle for maybe 20 minutes, or a 5-gallon bucket with three 1/8″ holes drilled on the side at the bottom and filled 2-3 times consecutively works great.
If the temperature gets over 90 degrees, bump that up to twice a week. If we see another heat “event” coming, a good, deep soak beforehand is very wise as preventative medicine.
Most people by now are fairly well attuned to the benefits of trees environmentally, socially, mentally, and more. However, less people are aware of how tree canopy is distributed among a city and its neighborhoods.
A trend across the country in large cities is that trees, and the benefits they bring, are distributed inequitably across neighborhoods based on race and income. Higher income neighborhoods with majority white residents have over 75% tree canopy coverage as compared to lower-income neighborhoods with around 15-30% canopy cover. These are large discrepancies that result in hotter environments, more air pollution, and factors contributing to respiratory conditions like asthma for children.
These trends are reality here in Portland: west Portland (excluding Forest Park) has about 75% canopy cover in most neighborhoods, while east Portland neighborhoods average about 15-30% canopy cover. Friends of Trees prioritizes planting street and yard trees in neighborhoods on the eastside of Portland to help decrease this disparity.
However, many people are wary about – if not outright opposed to – getting a tree of their own because of the costs of tree care, which can increase as a tree grows. This is just one of the reasons Friends of Trees provides tree care along with tree planting, including proper pruning of young trees at no cost to the property owner. And we’re exploring ways to increase the availability of low to no cost tree care for folks who need it, because we know the benefits of trees far outweigh the costs.
In the City of Portland, tree care and maintenance costs are the responsibility of the tree’s adjacent property owner. This is an inequitable financial burden for low-income households, renters, and populations vulnerable to gentrification. Many communities of color cite the financial burdens that a mature tree can bring as a reason to not want to plant trees next to their houses. It’s important to address these very valid concerns since trees have so many benefits, which is why Friends of Trees is continually working on creating programming that is responsive to community needs; in fact, we have funding proposals pending with Portland’s Clean Energy Fund that would help subsidize costs of mature tree care so we can grow our already considerable post-planting tree care services.
Understanding concerns about tree care
In 2018, Friends of Trees partnered with APANO and LARA Media to conduct three focus groups toward better understanding how community members viewed neighborhood trees and tree planting efforts. To increase accessibility these focus groups were conducted in multiple different languages including Vietnamese, Mandarin, and Spanish. Overall, many community members cited the benefits of trees within the city, including their health and environmental benefits:
“Trees are good for the lungs. They are the lungs of the city.”
“In the city, there’s big trees that make the air cooler. It also makes the city greener.”
–participants from the Vietnamese focus group
However, when asked if there are barriers for them to plant trees, many community members cited the long-term costs associated with mature tree care. One participant said: “One of the negatives is that sometimes Portland has a lot of storms and trees fall down when there’s strong wind. I experienced that once. The tree can fall into the house and collapse the house. Usually I try to hire a professional to cut the tree, but it [can cost] thousands of dollars. The tree bothers us.”
Trees and access to the natural environment are integral to healthy, livable neighborhoods. The benefits trees bring are strongest when they are mature, at least 10-15 years after they are planted. However, the fears community members have about the costs trees may bring are also valid, especially since the median household income on the eastside of Portland is lower and there are fears of being pushed out.
Friends of Trees is committed to equitably growing the urban forest through community-centered tree plantings. We offer tree care for the first three years of a tree’s life after it’s planted, including affordable (or free if cost is a prohibiting factor) summer watering service; free mulch; and structural pruning provided at no cost (see the next story for more about our pruning program). Structural pruning on a young tree is vital for its long term health, and can help prevent limbs falling onto a house or car later on in its life, since we can prune for the built environment and the tree will grow into that structure.
However, Friends of Trees also recognizes there are long term costs and concerns that need more support within our communities to make sure the urban forest is distributed equitably. We are continually working on creating programming that is responsive to community needs and when the opportunity arises we pursue grant funding to help subsidize costs of mature tree care. Because we know that, all in all, the positives of trees far outweigh the negatives; as our good friends at J Frank Schmidt like to say, “Trees are the answer.”
Photo: Street tree planting in east Portland, January 2020.