Hello fellow readers, Anthracnose (Ann-thrack-nose, my phonetics) is the most talked about and the most serious amongst the doggone dogwood dilemmas. Though powdery mildew, leaf and flower blight spot and crown canker also rank high. Never mind the dogwood borer, which can run amuck. It turns out, according to the Old Farmer’s Almanac, anthracnose affects many plants, and the fungi are spread quickly during rainy seasons.
The Penn State Extension Office’s website has a nifty spreadsheet titled Dogwood Diseases with photos to help ID the dilemmas. It’s organized in columns by diseases name, symptoms, pathogens (a fancy way of saying what caused the disease), and how to manage each. The anthracnose and decline pathogen’s scientific name is Discula destructiva. You don’t need to know Latin to know what that means – it’s destructive. In fact, deadly over time, which is why the much-loved native dogwood (Cornus florida) is rarely seen thriving along wood lines where they love to live. And, the pure species are long gone from nurseries as far as I’ve seen.
Symptoms start with brown spots on leaves, up to a quarter-inch, that often progresses to the tips of leaves becoming blotched with brown dead tissue. The lower branches begin to die on which acne seems to appear – pimply red bumps, which are the fungus’ fruiting parts. When in bloom, the bracts can be spotty, which is pretty, like reddish freckles, until the spots turn brown and distort the bracts. As you would guess, humid soggy conditions such as we’ve had have exasperated the dilemma.
What to do? Rake and destroy leaves that have fallen but don’t remove and destroy the dead twigs until the tree is dormant. For now, please take note of the bad branches and remove them in late fall or winter. Next spring, you can apply a fungicide to protect the flowers, leaves, and branches during budding. It’ll be challenging to reach the high parts and keep up with spraying every two weeks until the leaves are fully unfurled. It may be best to hire a high-reaching professional.
The bottom line, they suggest replacing dying trees with a hybrid of Kousa Dogwood (Cornus kousa, the hardier Asian species) and our native Flowering Dogwood (Cornus florida). Rutgers University has been a pioneer in this hybrid lead by Dr. Elwin Orton. He brought to market the Stellar series of dogwoods in 1990, including Cornus ‘Rutgan’ Steller Pink, Ruth Ellen, and Constellation. All are resistant to the gambit of dogwood diseases, including anthracnose and powdery mildew. However, the form of the Steller series of dogwoods is more vase-shaped than the much-loved broad-reaching canopy of the Flowering Dogwood. Still, they are magnificent trees. It took Orton a quarter of a century to breed, evaluate, and improve the hybrid before bringing it to market. Yup, it takes that long to tackle the fungus amongst us with such beauty and grace. Garden dilemmas? AskMaryStone@gmail.com