Summer Tree Issues

Each August, the arborists at Ross Tree assess summer tree issues they faced in Denver. The tree insect and disease issues we find each summer depend on what happened in the winter and spring seasons. Sometimes Denver has wet winters and springs, and other times both are dry. Or it can be a mix of wet and dry months. The amount of moisture produces a unique set of tree diseases and insects to treat each year. In 2022, we had a bone dry winter and a wet June. So this year’s tree issues are Aspen Cytospora, Honeylocust Thyronectria, and soft-bodied tree insects.

What Happens to Trees During a Winter Drought?

Denver tied a record set in 1887 for the most days without measurable snow. The trees that took the brunt of this year’s winter drought are Aspen and Honeylocust trees. Desiccation hit these trees’ shallow root systems hard. Desiccation is when the amount of moisture lost by the tree exceeds the amount of water taken in by its roots. Extreme dryness in trees occurs during freezing weather with high winds or prolonged periods without snow cover. Deciduous trees with dried-out root tissue starve because the root systems’ lose their ability to store and transport food. Also, winter drought kills branch tissues turning them dark brown in the spring. Once tree tissue dies, it does not grow back. An arborist should prune out all dead branches and twigs to make room for new growth during the warmer months. Evergreen trees have the same problem with their needles and branches drying out and turning brown.


Trees weakened by drought become susceptible to disease. Aspens in Denver have been hit hard by Cytospora, which quickly attacks plants stressed by drought and injury. The fast-growing fungi colonize recently dead tissues as saprobes. Saprobes are decomposers that feed on dead and decaying wood and other organic matter. As they grow, they girdle the tree killing it. Denver neighborhoods are now full of denuded Aspens. These leafless trees will need removal.

Thyronectria cankers

Thyronectria cankers are harming and killing Honeylocust across Denver. Disease symptoms include branch dieback, reduced foliage, premature fall coloration, and early leaf drop. If large abscesses appear on the trunk of trees, they will die and need eventual removal. Click here for more information about Thyronectria cankers.

Unfortunately, once established, there are no cures for these two cankers. The best way to keep Aspens and Honeylocust fungus-proof is by signing up for a deep watering maintenance program with Ross Tree. We take the fuss out of tree watering and have the equipment to water the biggest trees found in Denver.

Soft-Bodied Tree PestsĀ 

Honeylocust Aphid

After the 235-day drought, Denver experienced a wet June, which created perfect growing conditions for Aphids and Scales. These sap-sucking insects targeted Spruce and Maple trees this year. Homeowners finding honeydew messes on the patio furniture, driveways, and sidewalks should give Ross Tree a call. For more information about Aphid control, check out our blog titled “Surprising Rise in Tree Aphids This Summer in Denver.”

Early Fall Colors on Trees

Grass eater and lawn mower mechanical damage

The Autumn Blaze Maple is turning to its fall colors in August, which indicates a tree is in distress. Stress can come from desiccation, tree insects, or disease. The tree above has succumbed to careless mowing and grass trimming around its base, causing mechanical damage. Over time the trunk was girdled, robbing the rest of the tree of nutrients from its root system. The tree also has sunscald. The tree’s vascular system is shutting down and dying, so it needs removal. The pretty caterpillar on the trunk is an American Dagger. As its name implies, the insect is venomous and should not be touched. The Caterpillar lays eggs on rotting wood in late summer to overwinter and hatch next spring. These caterpillars are another indicator of tree stress. When doing lawn work, be sure to avoid hitting the trunk of trees with mowers and weed eaters.

Since most trees growing in Denver yards are not native, it makes sense that these plants need extra watering throughout the year. Please click here to schedule a deep root watering service or call 303-871-9121