Dogwoods are dying. It's a sad fact but a lot of Dogwood trees in America are getting sick and in many cases dying from Dogwood Anthracnose, a disease that mainly infects flowering and Pacific Dogwood (Cornus florida and C. nuttallii). However, this is a sad story that seems to have a happy ending, as I'll explain in a moment.
Dogwood Anthracnose is caused by the fungus officially known as Discula Destructiva, and it might be helpful if I describe some of the symptoms. The first sign of infection can often be seen on the leaves, where you might see tan spots that develop purple rims. Leaves may also have necrotic veins and leaf margins, and large necrotic blotches.
Another indication is what's known as twig die-back, and this in turn often results in the appearance of succulent shoots on the lower trunk and main branches of affected trees. On the trunk and limbs, you might see cankers and lesions with purple or reddish borders. Split bark and swellings often are external indicators of these cankers.
The infection appears to be aided by cool, wet weather, and infection seems to worse in trees growing in shaded or high-humidity areas.
What can you do to control Dogwood Anthracnose? Unfortunately, once the tree has been planted there isn't much you can do. A fungicide such chlorothalonil, mancozeb will protect against leaf infections and needs to be applied before symptoms appear. Dogwood trees planted in a sunny, open environment are less susceptible to the effects of the infection.
If you suspect your Dogwoods are infected, or if you want to find out more about the disease, you can find a lot of very useful information at this USDA Forest Service website: http://www.na.fs.fed.us/spfo/pubs/howtos/ht_dogwd/ht_dog.htm You can click on a direct link to that page by visiting my website and finding this column in the section titled "The Plant Man". There, you will also find a link to another useful site: http://fhpr8.srs.fs.fed.us/pubs/dogwood/r8-pr26/dwr8pr26.htm which also gives a brief history of the disease that was first reported in the United States in 1978.
But now for the good news!
There is one (and so far, only one) Dogwood cultivar that is resistant to Anthracnose. It is known as "Appalachian Spring" and was developed by the Tennessee Agricultural Experiment Station in 1998. However, it is only now, in 2002, that Appalachian Spring has been made available to the retail market. (I should add that the variety known as Kousa Dogwood also shows some resistance to the disease.)
And the good news gets better.
Appalachian Spring is a very attractive Dogwood with large white "bracts" (they look like petals) and large foliage that is candy-apple green, turning to brilliant red in the Fall. So this cultivar is by no means a second-rate Dogwood, and it's reassuring to know that it will resist the dreaded Anthracnose.
Note: Our sponcer Greenwood Nursery, will be offering the Appalachian Spring Dogwood on its website in the next week or two.
Take a look at the two websites I mention above for a lot of information about caring for your existing Dogwoods. And if you decide to plant new Dogwoods, you might want to consider the new disease-resistant cultivar, Appalachian Spring. As always you are welcome to contact me if you have any concerns about your Dogwoods or any other landscape-related problem.
The Plant Man is here to help. Send your questions about trees, shrubs and landscaping to steve@landsteward.org or mail to: Steve Jones, "The Plant Man", P.O. Box 686, McMinnville, TN 37111. For resources and additional information, including archived columns, visit www.landsteward.org
QUESTION: "Are you able to help us? Our landscaping plants are growing (too) vigorously. Are we now able to trim? If so, when? These are the plants: Globe Arbovitre, Burning Bushes, Hosta 'Krossa Regal', Hydrangea 'Tardive', Spirea 'Little Princess'. Your help will be appreciated." - Don & Carnetta
ANSWER: You should be able to trim all the plants except the Hostas. Hostas can be taken up in the fall after they have gone dormant and divided into smaller divisions. These can then be planted out in different locations. All of the shrubs that you mentioned can be trimmed after the initial flush of growth or blooming period. This will allow plants that bloom to set buds for the next year, and cause them put on a new flush of growth. The size and age of your plants will determine how much to cut off. For an older plant it may have already gone past the stage of being able to prune much and have it look good. In other words, if your burning bush is 8 to 10 years old you don't want to cut it back so much there is not any foliage left. Usually a rule of thumb is to trim and shape just above where this years new growth has occurred. This will cause more dense branching to occur this growing season. Cut out any of the dead wood that you find and water and fertilize after trimming. This will help to make your plants healthier and more productive in your landscape.
