Elm trees are towering beauties that bring much-needed shade to the Denver front range. Unfortunately, this species faces threats from several pests and diseases. Find out if you have elm trees on your property and how to keep them safe and healthy!
Elm Tree Species Commonly Found In Denver
There are different species of elm trees all over the globe, but here is a list of the popular varieties that thrive on the Front Range:
This large deciduous tree will grow to approximately 75 ft tall and 70 ft wide when mature, providing plenty of shade under it’s beautifully shaped canopy. Its ability to grow quickly, in many types of soil, makes it highly desirable in zones 2-9. The American elm is well suited to Denver because it can handle urban conditions and is resistant to drought. This produces 6 inch textured green leaves which turn vibrant yellow in the fall.
Also called the Weeping elm, this large accent tree is a stand out with its graceful, draping limbs and sweeping low canopy. The Camperdown elm produces rich colored dark green leaves and grows best in Denver’s zone 5. This elm species are known to be low maintenance and just needs full sun and room to spread! At maturity, it stands about 20 feet tall and 30 feet wide. This species is doing well in Denver due to its tolerance for high soil pH levels, urban conditions, environmental salt, and pollution.
Known for its longevity, this elm species can live for over one hundred years! The Cherry-bark elm should only be planted in wide open spaces because in adulthood it towers at about 100 feet tall! This beautiful giant produces bright green leaves and flowers during April and May. It is tolerant of several soil types but prefers to grow in zone 5. This species is also sought after because it defends itself well against Dutch elm disease.
Another elm species known for standing up to the Dutch elm disease is the Chinese Elm. Standing 40-50 ft tall, this variety shares the same shape as the American Elm. It also has the noticeable flaky trunk that adds interesting texture and color to any landscape. The Chinese elm is native to Native China, Japan, North Korea, and Vietnam, and grows well in the U.S. throughout zones 4-9.
The David elm is one of the smaller elm varieties, reaching approximately 30 ft tall at maturity. This Asian elm species originated in China, Japan, Korea, Mongolia, and Siberia, and can thrive in the U.S. in zones 3-8. The David elm has a reputation for being hardy and can thrive in Denver due to its reduced size, urban tolerance, and ability to survive Dutch elm disease.
As its name suggests, this elm species originates from Eastern Siberia and Asian regions such as Korea, Tibet, India, and Mongolia. In the U.S. Siberian elms grow to up to 70 feet tall in zones 3-9. This hardy variety can withstand all types of conditions and thrive just about anywhere. No green thumb? These persistent elms are tough to destroy!
Looking to add some trees that offer more than just ornamental benefits to your landscape? The Slippery elm is known for its healing properties. Called ‘slippery’ due to the mucilage found in the inner bark, this variety’s bark is believed to have properties that can help treat ailments such as sore throats, irritable bowels, and heartburn. Slippery elms need room to grow because at maturity they can reach between 80-130 ft tall!
How To Identify Denver Elm Trees
Easily identify different elms in your neighborhood and community by looking for these key features:
- All elm tree leaves have a symmetrical base and doubly serrate margin at the tips
- An elm trees leaf shape is oval, with a point tip
- Look closely and you can feel that the leaves are thick, rough, and deeply textured
- The large leaves are normally about 7 inches long
- Bark is relatively smooth on young adolescent trees
- Mature, older trees develop a textured, rough bark
- Slippery elm trees are easy to spot by looking at their smooth inner bark
- Bark is typically grayish brown with irregular ridges
- Elm wood is sought after for its high density
- The elm trees textured grains create a unique pattern in the wood
- Elm wood is resistant to splits and decay, perfect for carpentry
Elm Tree Diseases
Several life-threatening diseases are common among Denver elm trees. Knowing the dangers elm trees face is the first step to preventing them!
Dutch Elm Disease
Dutch elm disease is an aggressive fungal disease spread from tree to tree by the elm bark beetle and is the highest threat to American elm trees in the United States. The fungus blocks the trees water conducting and vascular system, resulting in death within the year.
Elms diagnosed with Dutch elm disease must be removed and disposed of, for the health and safety of all other trees nearby. If detected very early, it is possible to manage the disease by removing affected branches.
This common disease affects several shade tree varieties in Colorado. It attacks the trees inner core, creating bacterial slime that is toxic to the wood. Visible signs include yellow discolored wood, wet-looking bark and sometimes a slimy, foamy white ooze. Unwanted pets are sometimes attracted to this slime.
Cytospora canker is a fungal disease that occurs on parts of elm trees that are stressed. The canker-causing fungi cause girdling of the plant, killing the plant above the canker. The Siberian elm is known to be susceptible to this disease.
Elm Tree Infestations
Denver elm trees are plagued by a few different pests, but luckily you can protect your trees with proactive treatment. Colorado State University Extension offers these quick fact details on each pest:
- Aphids are found on almost all types of plants and a few species can cause plant injury
- Some aphid species can curl the new leaves of some types of plant
- Feeding aphids excrete honeydew, a sticky fluid that can attract other unwanted pests
- Leafminers are insects that feed within a leaf, producing large blotches or meandering tunnels
- Leafminer injuries are conspicuous but have little, if any, effect on plant health
- Insecticides applied when leafminers lay eggs are useful for control of many leafminers
Elm leaf beetle
- Adult elm leaf beetles chew holes in elm leaves, feed on the leaf surface, and create a lacy looking skeleton pattern
- Adult elm leaf beetles often spend winter in and around buildings and may be common nuisance invaders found within homes during this period
- Some insecticides that move systemically within plants can be applied to the soil to control elm leaf beetles
Elm Bark Beetle
- Elm bark beetles measure from 1/12 to 1/6-inch long and are covered in stiff, yellowish hairs
- Beetles dig small holes into trees and lay eggs underneath the bark layer
- Elm bark beetles spread Dutch elm disease
- Effective treatment involves killing the beetles before they bore into the bark in fall and when they first emerge in spring
Elm Tree Care And Treatment Options
Chemical controls can effectively control pests like elm leaf beetles, elm bark beetles, and aphids.
Treatment with Bacistat trunk injection: When your body has an infection, you take an antibiotic. Bacistat is an antibiotic for your trees! It can be applied yearly in April-May. We recommend treatment every 2 years to limit trunk damage. Bacistat will reduce only the twig stage, not the blossom stage of infection. Optimal results with Bacistat occur when applied prior to the onset of visual symptoms.
Elm tree fungal and bacterial diseases develop in trees that are stressed or injured. Healthy trees can fight off infection! Here are our recommendations on best seasonal practices for keeping elm trees in tip-top shape:
- Watering: proper watering is an overlooked but very important tree care practice. Some elm varieties are prone to fungi related diseases if their soil becomes too saturated with water, and other times the damage can occur if there isn’t enough water. We can provide expert consultation on how much water you should be giving your elms, and how often.
- Fertilization: for many elm species, even the ones commonly found in Denver, the high alkaline soil can lead to problems with chlorosis. The best way to neutralize this threat is with the right fertilizer application. Balancing the soil and getting your trees the nutrients they crave will keep them strong and healthy.
- Tree trimming: annual pruning and trimming help elm trees keep their beautiful shape and foliage. Trimming damaged or slightly infected branches can save the whole tree!
To learn more, schedule a complimentary on-site disease diagnosis of your elm trees. One of our arbor experts will walk you through our four-step approach for treating elm trees and create a custom plan for the unique needs of your trees!