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  • The Stewardship web page keeps you informed of current Arboretum staff activities. Here we share past articles from throughout the year
 

Past Events

Dying Pines on Washington Place East

Over the past 5 years we have been seeing both 5 needle (P. strobus, and related spp.) and 2 needle (P. sylvestris) pines dying along Washington Place E. It has accelerated in the last 2 years. 8-10 mature specimen pines have been removed to this date. Several existing pines are weak and the remaining healthy pines could be vulnerable. There has been much speculation as to the cause: drought, buried root crowns, neighbors dumping alkaline waste, wood boring insects and root disease. Recently, we had 2 UW/CFR professors, Bob Gara and Bob Edmonds, visit the site to inspect and evaluate. Their conclusions thus far: the wood boring insects found appear to be secondary. There may be the presence of Heterobasidium annosum (Fomes) – a root rot organism. Bob Edmonds will confirm this with a lab test and then notify us. The droughty conditions of the last few summers may be one of the main predisposing factors.

Large Picea orientalis Falls

Another significant (in size at least) collection blow down. WPA's largest (second tallest in Seattle),  Picea orientalis (831-47-B), 75' tall x 4.5" circum., located in Pinetum (Grid 34-5W), was uprooted Wed. late afternoon.
Picea orientalis falls winter 2006

Noteworthy Pine Downed in Winter Storm

The largest girth (over 6' circum) Pinus attenuata, Knobcone Pine, in Seattle was uprooted yesterday, February 1, 2006, during an early morning storm.  Due to both a high water table and lopsided scaffold branching, the shallow root system gave way under tension from the variable 25-35mph wind gusts and heavy rain. Located along Broadmoor fence, just north of compost bins, UWBG arboretum staff cleared the massive tree from the nursery road yesterday and will finish cleaning up today. A log will be salvaged and used along the trail in Woodland Garden. Other information:

  • Collateral casualty from downed pine: 1616-56-A Malus 'Henry F. Dupont' Grid 34-6E;
  • Acc#: 200-54-B Pinus attenuata Grid 34-7E(adjacent to 200-54-A) is in worse condition than downed pine and under similar circumstances it may also fail. Arborist Lou Stubecki recommends removal in near future to mitigate hazard to public and nearby collections.
  • New Accession: # 200-54-A Pinus attenuata Grid 34-7E;
  • Good News! The tallest Knobcone in our state is located in Pinetum. 81', as noted by Van Pelt in 1993.

 

 

 

 

 

 


Cherry Blossom Brown Rot

Cheery Brown Rot

Blossom brown rot is a fungal disease that is a perennial problem for cherries grown in our region. The fungus overwinters on infected twigs and dried fruit on the tree or ground. The fungal spores are spread in the spring by wind and rain through the blossoms, causing twig dieback. As part of the Arboretum’s Integrated Pest Management program (IPM) moving toward our goal of eliminating the use of all synthetic pesticides we have decided to experiment with not spraying the cherries this year with a fungicide.

IPM relies on many strategies to manage plant health care:

  • Proper ID of the pest and its life cycleRegular monitoring of the plantsThe use of physical, mechanical, cultural, and biological controlsChemical controls used as a last resort
  • Least toxic chemicals used

This year we are not going to spray the cherry collection with a fungicide to protect against brown rot infection. We will carefully monitor the trees this spring and summer to see how they fare without the usual fungicide treatment. With luck, and cooperative weather, we may find that the trees are not any worse off than if they had been sprayed. Trees that are badly affected and very important to the collection will be noted as candidates for spray next year. Our staff is researching the latest findings on the least toxic chemical controls available if they have to be sprayed next year. The other part of the IPM program involves the use of physical and cultural controls. The cherries are pruned in the summer to remove infected twigs and improve air circulation. Tree rings are given a fresh coat of mulch in the fall to bury any infected plant material that may be on the ground. In our Cherry Replacement Program we are only using cultivars that are resistant to Blossom Brown Rot.

 

Hazard Tree Removals

Hazardous Willow
  • This willow, Salix babylonica ‘Crispa’, located on the northeast side of Foster Island bridge, will be removed week of November 20th for public safety.
  • This tree has been monitored since before the Shoreline Restoration project and it is now slowly beginning to uproot towards the bridge.
  • Cuttings of this tree have been taken and will be eventually reintroduced into the UW Botanic Garden’s Salix collection.
  • Bridge will remain open during removal, although flaggers will be on-hand for safe crossing. PDF Flyer

 

This large, mostly dead Big Leaf maple (Acer macrophyllum), located in the Asiatic Maple area, is scheduled for removal Monday, August 8th and Tuesday, August 9th. Its accelerated decline due to verticillium wilt has deemed it a threat to public safety and surrounding plant collections. Many of our big leaf maples are dying due to age and disease. Each tree problem requires evaluation to determine the best course of action for the site.

 

Cherry Bark Tortrix

The Cherry Bark Tortrix (CBT) is a moth whose larvae bore under the bark of the trunks and limbs of cherry trees, causing gummy sap to exude from the tunnels, which can become extensive enough to girdle the trees. Infestations can weaken trees and increase their susceptablity to other pests and diseases.

(right - larval frass tubes, which occur around wounds, cracks, and naturally occuring lenticels)

CBT was first detected in Washington state at Peace Arch State Park in 1991. Nearly all the older cherry trees in Whatcom County were severly damaged or dying by 1993. As it's spread is noted through the State, it could be devastating to the culture of fruit and ornamental cherry trees.

The insect is common in Europe, but kept below damaging levels by natural predators.

Entomologists from Washington State University - Vancouver Research Station are studying methods for control, with strong interest in the use of natural predators. The researchers have been studying our trees for the past few years, and have noted a much higher infestation from last year. The Washington Park Arboretum is currently working with WSU on the study of our trees and methods for control.

For more information, please visit http://www.vancouver.wsu.edu/programs/cahe/wsureu/Ento.cbt.htm

Cherry Blossom Brown Rot

Blossom brown-rot disease is a perennial problem for cherries grown in our region. The fungus infects through the blossoms, causing twig dieback. Currently, the only control is the application of fungicide sprays three times during the bloom period - "popcorn" stage, full bloom, and petal drop.

The Arboretum employs a holistic approach to managing plant health problems, combining the use of carefully timed, least toxic control applications, cultural practices to improve plant vigor, and the removal of severely affected plants beyond restoration. Extensive monitoring and follow-up evaluations are a critical part of this work.

Twig dieback on Prunus subhirtella 'Eureka Weeping'

The Arboretum's flowering cherry trees along Azalea Way are treated each year. Signs are posted at the main entries to the Arboretum, and in the Graham Visitor Center. Small yellow signs are posted to treated areas, advising visitors not to enter those areas. In addition to carefully timed sprays, severely weakened trees are removed. With our damp wet springs, complete control is never achieved, and trees are pruned later in the season to remove dead twigs and branches. This also helps reduce the infection source for next season.

Cultivar testing: In planning for future plant replacement, the Arboretum has a test plot of cherries to evaluate cultivars that show resistance to infections. The goal is to eventually replant with trees that survive well with less spraying. This plot is located in the old nursery area east of Arboretum Drive.

Ivy Removal & Status

English ivy is one of the more serious weed problems at the Arboretum. An invasive, non-native plant, English ivy threatens natural environments and cultivated landscapes alike. There are over one hundred cultivars of English ivy, nine of which have been commonly used in landscapes throughout the Pacific Northwest. This year, the presence and removal of ivy is on everyone's minds, as four cultivars were recently added to the State Noxious Weed List with a Class C status.

Class C status weeds are "priority weeds" that are commonly found throughout the state. Class C status indicates that local, long-term programs may successfully control the weed.

English Ivy Cultivars: Gaining Status

Mature ivy flowerhead. Mature leaves are quite different from their juvenile counterparts.English ivy is an evergreen vine, usually with glossy leaves. Juvenile leaves have three to five lobes in the classic "ivy" shape. Plants remain in juvenile form for at least ten years.

Mature leaves are more triangular to diamond shaped (right, with immature berries). Mature portions tend to be more upright, producing flowers on the tips of vines in fall, which are insect pollinated. Dark blue to black berries mature in late spring, which are then spread by starlings and robins. The seeds have a short dormancy and germinate quickly, even in dry, shady conditions. English ivy is extremely long-lived; one plant in France was estimated to be over 400 years old.

The four cultivars are Hedera hibernica 'Hibernica', H. helix 'Baltica', H. helix 'Pittsburgh', and H. helix 'star'. Descriptions following are from Midori Murai's thesis (1999):

  • H. helix 'Baltica' is a vining plant. The leaves are usually 1.5-2 inches (3-5 cm) long, three-lobed, dark green, and leathery. H. helix 'Baltica' is very cold hardy.
  • H. helix 'Pittsburgh' has a "self-branching habit" ("shoots arise from every node"). The leaves are 1.5-2 inches (3-5 cm) long, five-lobed, medium green, and thin in comparison to other Hedera species. One of the fastest growing species, H. helix 'Pittsburgh' regularly reverted to the vining habit.
  • H. helix 'Star' also has a self-branching habit. The leaves are longer, 1.5-2.5 inches (4-6 cm) long, with five deeply cut lobes, and dark green. H. helix 'Star' is a "bird's-foot type," with leaves resembling bird's tracks. H. helix 'Star' grows quickly and commonly reverts to the vining form.
  • H. hibernica 'Hibernica' is a vining plant with 2-3.5 inches (5-9 cm) long leaves, five-lobed, and thicker thanany of the H. helix species. H. hibernica 'Hibernica' grows extremely rapidly and is considered to be responsible for over 80% of ivy invasions in the Pacific Northwest (Murai 1999).

It is important to note that not all English ivies are included in this listing. These four cultivars were extensively researched before being placed on the Washington State Noxious Weed Lists. These cultivars, however, are sold under a variety of names in the nursery trade.

English ivy seeding in bird's-foot ivy bed.Not all ivies are created equal (left)~ This slow-growing bird's-foot ivy has been invaded by an English ivy seedling.

History of Management Practices at the WPA

The thick, waxy leaves are nearly impervious to herbicides, limiting their effectiveness. Arboretum staff have had some success using herbicides, labeled for cut stump treatment, after cutting the ivy down with a brush cutter or weed-eater. The herbicide method, however, kills adjacent vegetation and should be used only when ivy is the sole plant in the area. Therefore, most control efforts rely on manual labor.

At the Arboretum, management of English ivy is perpetual, though it has been successfully removed in several locations.

Approach to Management

Removing ivy can be an overwhelming task, but plan to first control and then remove ivy for maximum management effectiveness:

  1. Remove flower and seed heads when they first appear. This greatly slows the spread by seed. Do this between October and March before seeds mature.
  2. Look at the boundaries. (right) Is the ivy reaching past property lines or into other undesired areas? Cut back ivy at the boundaries first, where spread may soon be out of immediate control.
  3. Remove vines from soil during dormant season. This is during the late winter/early spring when the moist soil facilitates root removal.
  4. Cut and cover - repeatedly! Repeatedly cutting off or mowing vegetative growth reduces ivy reserves and suppresses growth. Covering with a heavy layer of mulch will slow regrowth.

To learn more about ivy removal, please visit the No Ivy League ~ Ivy Removal Project.

For more information on noxious weeds and invasive species in our region, please visit:

Reference:

Murai, Midori. 1999. Understanding the invasion of Pacific Northwest forests by English ivy (Hedera spp., Araliaceae). Thesis. University of Washington.

Murai's thesis is available in the University of Washington's Forestry Library or the Elisabeth C. Miller Horticulture Library at the Center for Urban Horticulture.

 

 

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