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  • Writer's pictureJennifer Anderson

Dogwood Dilemma

A woman visited my nursery recently and asked whether I carry Kousa Dogwood (Cornus kousa).


Well, no, I carry only native trees. I showed her my native White Flowering Dogwood, Cornus florida, and I shared with her its susceptibility to mildew and other diseases.  She said she’d be back, and I haven’t seen her again.


Her visit, and others like it, highlights a dilemma: the desire to stay true to my native-plant mission while also providing beautiful, carefree trees people want to plant.


For many people, there is no substitute for a Dogwood.  Our native Flowering Dogwood is the most beautiful of all – “as close to perfection as nature is willing to tread,” says William Cullina in Native Trees, Shrubs and Vines.


It feels like a crime that this beautiful tree, with its loose, airy crown and large white bracts framing a small, central bloom, is so beset with problems that people are looking overseas for alternatives.


Dogwood Anthracnose


No one knows for sure, but fingers are pointing to Kousa as the culprit in the fall of the native Flowering Dogwood – “the prime suspect,” says the National Wildlife Federation.


The earliest known imports of Cornus kousa date to the late-1800s.  It wasn’t until the 1970s that imports of Kousa accelerated.  As more Kousas entered the country, so did a new fungus, Dogwood Anthracnose, first reported as a disease in 1978.  Kousa appeared immune to the pathogen, Discula destructiva, while our native Flowering Dogwood had no resistance.


Spot Anthracnose


While Dogwood Anthracnose has become less prevalent, another fungus has emerged, Elsinoë corni, causing Spot Anthracnose.  This disease is primarily cosmetic, causing spots, or dots, on the leaves and petals and curling of the leaves, especially after a wet spring.  The spots are tan with a purplish border and appear on the leaves, bracts and fruits.  The fungus overwinters on the twigs and is most severe during wet springs.


Mildew


Yet another fungus hit in the 1990s, Erysiphe pulchra, or powdery mildew.  The mildew coats the leaves and causes yellow and brownish patches, eventually causing the leaves to curl, droop and often fall early.


Powdery mildew weakens but does not kill the trees, although stress from the fungus can make the trees susceptible to borers and other pests that can kill the trees.


Changes in the climate, or in the pathogen, could have brought on the widespread onslaught.  


“My suspicion is that dogwoods have always been susceptible,” says Steve D. Pettis, of the North Carolina Extension.  “But because we plant dogwoods outside of their preferred situation, they get stressed and are therefore more susceptible to all kinds of health issues.”


Two Dogwoods


Kousa, which means Dogwood in Japanese, shares similarities with the native Flowering Dogwood, but also a few key differences.

  • Kousa blooms in May or June, after its leaves have come out, while our native Dogwood blooms in April, before the foliage emerges and just as pollinators are seeking early nectar sources.

  • Kousa has yellowish-white “bracts” that open up in a diamond shape to reveal the inner flower; Flowering Dogwood has white bracts that make more of a cross shape.



  • Kousa berries are pinkish-red, about an inch or so in diameter and a favorite of monkeys in their native Asia. 


  • Our native’s fruits are a half-inch red ovals rich in calcium, proteins and fats beloved by birds and also quail, black bear, foxes and deer.


  • Kousa does not support any caterpillars.  Cornus florida has very high pollinator values and is a larval host to the Spring Azure and more than 20 other butterfly and moth species.


  • Both trees have a reddish-purple fall color.


Emerging Invasive


Kousa offers little ecological benefit to insects and birds.  Squirrels do eat the fruit, and this may be the reason Kousa dogwoods are invading natural areas, to the extent New Jersey has declared the Kousa an “emerging invasive” – a plant that has demonstrated the potential to become a widespread invasive species.


What to Plant?


If you have your heart set on a Flowering Dogwood – and who could blame you – and you think you have the right spot and are willing to manage the tree, go for it.  


Nothing is easy, right?  There are differing opinions over whether Flowering Dogwood is best placed in the sun or shade.  UMass Extension advises full sun, given an inverse relationship between sunlight and anthracnose. 


Pettis, of North Carolina, however, notes that Flowering Dogwoods grow naturally along forest edges.  “It is when we place them out in open spaces where the soil is too hot they get stressed.”


Soil compaction from heavy mowers and mulch – not enough over the roots and too much around the trunk – also can stress the trees.  Dogwoods also benefit from good air circulation and strategic pruning to keep the canopy open.


Also consider applying an organic fungicide, especially after a wet spring, twice weekly from bud-break through the end of July.  


Resolution


While I would never carry a non-native, I understand the desire to plant and enjoy a tree without a lot of maintenance. To that end I am considering two native, mostly disease-resistant cultivars of Flowering Dogwood, both in the Cherokee line.


Cherokee Brave, ‘Comco No. 1,’ has red bracts that fade to white in the center.  It is resistant to mildew and spot anthracnose but not anthracnose.  


‘Cherokee Princess’ has extra large white bracts and high resistance to spot anthracnose.  If mildew is present, this cultivar responds well to fungicide applications.


Other Options 


If an alternative to Flowering Dogwood will do, consider:


  • Pagoda Dogwood, Cornus alternifolia, not quite matching the beauty of Cornus florida but with a lovely branching pattern that looks like a pagoda. Pagoda Dogwood is resistant to anthracnose but has some susceptibility to spot anthracnose.  


  • Blackhaw Viburnum, Viburnum prunifolium,a beautiful tree that attracts all kinds of wildlife.  Blackhaw technically is a shrub but can be trained as a small tree, getting up to 20 feet.  It has clusters of white, spring flowers, edible blue-black fruits and reddish fall foliage.  


  • Sweetbay Magnolia, Magnolia virginiana, with creamy white blooms and high pollinator values.  Sweetbay is considered rare and endangered in Massachusetts.


  • Serviceberry (Amelanchier, spp.), a beautiful tree with early spring blooms, lovely foliage, edible blue berries and reddish fall color.




Climate-Smart Gardening


For gardeners looking for unusual plants but wanting to avoid invasives, Invasion Ecology Researcher Bethany Bradley recommends “climate-smart gardening,” the practice of choosing plants native to slightly warmer climates.


One of the main reasons species become invasive is because herbivores don’t munch on them.  Most plants south of New England evolved with the same bugs and mammals we have up here, and therefore the likelihood of them becoming invasive “is really quite low,” she says.


A Few Options 


Jersey to Florida and with very high pollinator values and host to several butterfly and moth caterpillars. White fringetree gets about 20 feet tall and in spring is covered with fragrant, frilly blooms.  Birds feed on its fall fruits.


  • Sourwood, Oxydendrum arboreum, native from Pennsylvania south and also with very high pollinator values.  Sourwood also is called Lily-of-the-Valley Tree because its mid-summer blooms look like strings of bells.  Sourwood has red fall foliage, sometimes turning while the flowers are still blooming.


Outliers


  • Carolina Silverbell, Halesia carolina, is definitely stretching the concept of “nearby native,” given its primarily southern range.  It is hardy to New England and a featured plant at Garden in the Woods in Framingham, Mass.  This tree has medium pollinator values but still is a larval host to three moth species.


  • Yellowwood, Cladrastis kentukea, likewise is native to Virginia and areas south but hardy to New England.  It

gets a little bigger than Flowering Dogwood, 30 to 50 feet, and it attracts butterflies and native bees.  Yellowwood is one of the rarest of our native trees and, says Cullina (Native Trees, Shrubs and Vines), “one of the greatest and yet most under-appreciated of our flowering shade trees.”   


Fun Fact ☺: The name dogwood apparently originated in Europe. The bark of one of the European species was boiled in water and used for washing dogs suffering from mange.  


 

About the author:

Jennifer Anderson is the owner of Tree Talk Natives, a native tree and plant nursery in Rochester, Mass. She loves to talk native plants and can be reached at jennifer@treetalknatives.com.



 

Sources:


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