Dr. Dave Clement, University of Maryland Extension Plant Pathologist, explains two common diseases of this popular evergreen tree.
Colorado blue spruce trees, although not native or adapted to Maryland, are commonly planted in landscapes for their attractive color and shape. There are, however, two plant diseases that commonly infect and disfigure them. Both diseases also can occur simultaneously and progressively speed up the decline of this popular tree.
I was very excited to have the opportunity to take a winter tree identification class. I attended a great University of Maryland Extension (UME) Master Gardener Advanced Training course with UME native plant specialist Sara Tangren last week. I assumed we’d be looking at bark. The classroom at the Extension in Westminster was filled with tree twigs… not bark.
I never took the time to really notice the details of a twig. The opposite leaf pairs on the stem are opposite side to side, then front to back. I never paid attention to that simple pattern. I recognized new stem growth and last years’ growth, terminal buds, leaf scars, vein scars, lenticels, etc.
Maple twig buds and leaf scars are opposite. A trick to remember trees that have opposite leaves is “MAD Horse Buck” – Maple – Ash – Dogwood – Horse Chestnut – Buckeye!
How well do you know your trees? Can you identify the trees in the images above? Do you know where to start and what to look for?
When we get tree identification questions at the Home & Garden Information Center, we look not only at the leaves or needles but also the leaf arrangement along the branches, the size and shape of the tree, the bark, buds, and fruits too.
If you want to get better at tree identification, like most anything, it helps to have a good foundation and to practice. If you are interested in getting better at tree identification, you may be interested in the upcoming events we are sponsoring.
We’ve recently received inquiries about oak trees declining and dying. People usually want to know if this is caused by oak wilt. Importantly, oak wilt is not known to occur widely in Maryland. Two common leaf diseases of oaks in Maryland are oak anthracnose and bacterial leaf scorch of oak.
Oak anthracnose is caused by a fungal pathogen, Apiognomonia quercina, and it typically is a cool, wet weather, springtime disease. In wet cool summers like the one we’re experiencing this year however, the symptoms can continue through the season. Most oak species will show a range of symptoms scattered through the leaf canopy. Symptoms range from small brown spots and irregular dead areas on distorted leaves to severe blight that kills twigs and causes leaf shriveling. This disease in oaks typically doesn’t cause much leaf drop.
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Q: I have a cherry tree that has been in the ground for three years and has grown well. This year, the leaves have holes and they are falling to the ground already. The tree was sprayed twice with an insecticide and a fungicide. All sprays have been at the recommended dilutions. The leaves continue to fall. What is the problem?
A: The foliage of your tree looks like it was subject to cherry shot hole disease. Infected leaves will turn yellow and drop from the trees in mid-summer, if the infection is severe. This disease can be common when we have wet spring weather. The pathogen may continue to infect leaves throughout the growing season if rainy weather persists. In most cases, trees recover from this disease and no treatment is necessary. Rake and dispose of fallen leaves in the fall to reduce overwintering pathogens.
In addition, be sure to identify a pest or disease before you decide to spray. Some insecticides are “broad-spectrum” products which will also harm many beneficial insects. Also, an insecticide will not do anything to treat a fungal or bacterial disease.
Learn more about cherry shot hole on flowering cherries and how to manage it.
Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask Extension.
Q: Do bagworms kill trees?
A: If there is a large infestation of bagworms on an evergreen tree, it is indeed possible for them to kill the tree if the defoliation is severe. Bagworms can be a problem on deciduous trees as well, but they typically do not kill them.
Bagworms are a common pest in Maryland and we receive a lot of questions about how to deal with them. Fall and winter are the best time to remove and destroy the bags that contain the eggs.
Here are a few tips about the lifecycle of bagworms and how to control them. Continue reading
Q: I have two beautiful, mature Leyland cypresses in my yard. I noticed that their tips are turning brown in spots. I see the same phenomenon on my neighbor’s evergreens that border my yard. Is this a disease? Do the trees need to be treated?
A: The brown tips on Leyland cypresses at this time of year are a symptom of Seiridium canker, a fungal disease. When these trees are stressed due to drought, poor planting techniques, and/or poor drainage, they can be susceptible to disease and insect issues. If the trees are planted too close together, there is a lot of root competition for moisture and nutrients, and the trees will also suffer from a lack of sunlight and poor air circulation.
There is no treatment for Seiridium canker. The brown tips will drop off naturally. Prune any dead branches during dry weather. The best recommendation is to keep the trees well-watered during dry periods. Keep mulch no thicker than several inches deep and away from the base of the trunk. Avoid over-fertilization. Leyland cypresses grow best in full sun with plenty of air circulation and appreciate moisture during dry periods.
Have a plant or pest question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask an Expert.
