Common Tree Issues

All trees should get supplemental watering for at least the first 3 years after planting. Be aware that a tree’s water needs will vary by species. Selecting drought tolerant trees will save money on watering over the lifetime of the tree. All trees benefit from additional water throughout their lifetimes, especially in periods of excessive heat and drought, and even more so if their water needs are high. Remember that we live in a high, arid desert and our average rainfall amounts are much lower than what some of these non-native trees require. Add mulch (2-4” thick but not directly against the trunk) to help retain moisture and protect the roots from excessive temperature changes. Consider winter watering if it has been a very dry winter. Water on warm days when the water can penetrate into the soil.

Freeze damage may occur because of large fluctuations in temperatures in the fall or spring; when trees are not fully prepared for winter, or when they are preparing to leaf out in spring. Severe and rapid temperature changes can lead to desiccation of plant tissues and canopy loss. Most often, fall damage is noticed the following spring when the trees don’t fully leaf out. Spring freezes may impact early flowering or budding trees by freezing fragile new growth. The tree has to use additional resources to produce a second set of buds. Although it may take several additional weeks, trees can often recover on their own, especially if they were generally healthy in previous years. Supplemental watering during dry periods may also be helpful.

Here are a few things to consider when assessing a tree with significant freeze damage or delayed bud-break:

• Are the branches supple, or do they snap easily? Suppleness means that the tree may have a chance of a second leaf-out. Brittleness is not as good; the individual branch or the entire tree may need to be removed.
• Was the tree fine in the last few years? Healthy trees are more likely to recover. Trees that were already stressed may not be as likely to recover.
• Compromised trees from extreme weather events may also be more susceptible to insects or diseases; watch for increased activity around damaged trees.

What can be done?

• Wait and watch for signs that the tree is leafing out.
• Support the overall health of the tree: water slowly and deeply under the dripline (area beneath the canopy) every one or two weeks. Let a hose trickle slowly for half an hour or more while moving it around the base of the tree. Check the soil moisture to help determine when it is appropriate to provide supplemental watering.

Read the label before applying any herbicide. We have been seeing an increase in sudden tree death (2019) due to improper applications. Many readily available weed control products contain imazapyr or imazapic, which can be harmful or even fatal to trees. Be wary of products marketed for “season-long control” or “extended control” of weeds.

If using a product known to be harmful to trees, avoid applying it within the dripline (area beneath the crown of the tree), and consider that tree roots are concentrated in the upper 12-18” of soil and may extend in a radius 2-3 times the size of the above ground crown.

Cutting a limb too close to the trunk (flush cut) removes critical tissues that can help the wound callous over to protect the tree from disease and decay. Likewise, cutting a limb and leaving a stub also slows the tree’s response and can lead to increased decay. Learn about proper pruning techniques courtesy of Ed Gilman at the University of Florida, but also consider calling a certified arborist to assist you.

Read more on the Colorado State Forest Service website. Click on Trees and explore the publications under Tree Selection, Planting & Care.       

Consider adding a layer of wood mulch underneath the tree’s canopy (2-4” deep and not directly against the trunk) to eliminate the need to cut grass immediately next to the trunk. Be mindful of shallow roots and avoid running a lawnmower over them on a low height setting.

Fruittree leafrollers are native moth larvae that have been observed in large populations over the last few years. The larvae (caterpillars) emerge for a period of a couple of weeks in late May to mid-June (weather dependent) and feed on leaves of many species of trees (crabapple, honeylocust, ash, hackberry, linden, maple, etc). This may cause partial or complete defoliation of trees or nuisance silk webbing and larvae around leaves and trees. Mature and healthy trees will survive extensive defoliation and regenerate leaves after the leafrollers have pupated. Typically, once the issue has been noticed (extensive defoliation and silk webbing), it is too late for any treatment to be effective, as the larvae are cocooned in leaves.

While City Forestry does not have the resources to spray right of way trees, adjacent property owners or businesses who wish to take preventative action may request a free permit to have a licensed tree service spray dormant season horticultural oils (best applied before bud break in the spring to smother egg masses), or contact-insecticides (best applied after bud break to control larvae before leaf rolling activity occurs). Please consider consulting with an arborist to determine the best method for your trees.

Cutting roots for driveway expansion, sidewalk repair, xeriscape conversion, or other construction could significantly affect the health and stability of a tree. Consult an arborist when planning projects.

Construction vehicles or even just parking a personal vehicle close to a tree can compact the soil and make it difficult for the tree to absorb sufficient water, nutrients, and oxygen. Consult an arborist or designate a tree protection zone close to the tree. The majority of compaction occurs in the first few passes and is extremely difficult to reverse.

Though storm damage is not always preventable, you can improve tree outcomes by consulting with an arborist about the need for structural pruning. Training young trees during the first 10 years after planting can have the greatest effect on long-term tree structure. Minor pruning of young trees improves long-term structure and strength, while maintenance pruning of mature trees can significantly improve tree resiliency by identifying weak areas and proactively reducing potential hazards.

Consider how you will need to maintain a newly xeriscaped area. Will you need to apply herbicide to prevent weeds? Will you stop watering? To protect trees during a xeriscape conversion, consider applying an area of wood mulch to retain moisture and moderate temperature. While rock mulch may seem to be an attractive and more permanent solution, it can increase soil temperature, which is detrimental to the tree roots, and makes cleaning up fallen leaves more challenging.

Trees that were not completely dead may still have resources and energy left in their roots. If these trees were removed without stump treatment or stump removal, sprouts may grow. These sprouts often grow into shrub-like, multi-trunked trees.

Read more here.