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Posts Tagged ‘crepe myrtle’

Drought and Heat May Have a Long-Lasting Effect on Urban Trees

Easter red cedar vs Leyland cypress

Native Eastern Red Cedar (left) has proven to be more drought and heat tolerant than it's non-native counterpart, Leyland Cypress (right)

It may be a few years before we fully understand the impact of last summer’s drought and heat on our urban forest.  The immediate effect is quite blunt.  Whether from relentless heat or lack of water, many trees have died.  The most obvious losses include Southern Magnolias, Leyland Cypress, Japanese Black Pine, and other broadleaf evergreens and conifers that continue to retain their damaged brown foliage.  It will be May before we can better assess deciduous trees.

We have made some early observations that could help you in caring for your trees or factor into selecting replacements.  Trees that are generally in good health have not been as negatively impacted by the drought and heat as those already stressed.  This is apparent when comparing mistletoe infested Cedar Elms with their clean counterparts.  The same can be said of Bradford Pears and other trees that are highly susceptible to Cotton Root Rot.

Trees native to North Central Texas fared better than most introduced tree species.  Post Oaks are the first to come to mind.  Even on non-irrigated sites, Post Oaks’ leaves remained glossy and green until fall.  Pecans seem to have fared well, too—some even producing a crop.  The exception to this observation would include Crepe Myrtles.  From the old standards to the latest improved varieties, Crepe Myrtles are proven tree selections.  However, Silver Maples have reconfirmed their place as a poor choice for local landscapes.

Magnolia Heat and Drought stress

Heat and drought damage to many Magnolia trees is severe enough to consider removal

Mulch continues to serve as a tree care staple.  A simple 2 to 4 inch layer of mulch covering a tree’s critical root zone retains moisture and insulates soils.  Both newly planted and well-established trees have benefited from the buffering effects of properly mulched trees.  There is added benefit in the nutrients made available to a tree’s root system when mulch decomposes into compost.

Adequate watering, regular fertilization, and appropriate tree care are practices that have a measurable effect on a tree’s ability to address stress.  Should you have questions or concerns about the trees in your landscape, a Certified Arborist is available to assist you.  Simply call our office or complete a service request.

How To Prune A Crepe Myrtle

By: Steve Houser

In order to know how to properly prune any plant, a basic understanding of the characteristics and growth habit of the plant in our area is required. A Crepe Myrtle is not quite like any other local plant in how it grows, and is therefore not like others when considering how they can be pruned. A Crepe Myrtle is an ornamental plant that blooms profusely throughout most of the growing season. They can grow to over 25’ tall, are very hard wooded and the small twigs or old seed pods do not produce new growth in the spring (like most plants). Tip growth normally dies back approximately 7-12 inches in the winter months. If a Crepe Myrtle is not tip pruned by spring, the new growth will emerge approximately 7-12 inches from the old seed pods. This leaves dead tips as it emerges in the spring. Since Crepe Myrtles are rapid growers, the new growth will rapidly obscure the view of the dead tips within a few months. The dead tips are of no great consequence to the overall health of the plant. Aesthetically, the dead tip is not attractive for the first few months of the growing season. They are also known for producing root sprouts that grow upward from the outward growing roots or near the root collar (or root crown).

The three factors that must be considered in the pruning of Crepe Myrtles are health, aesthetics and cost or time to maintain the desired condition.

Crepe Myrtles are hardy plants that can sustain moderate freeze damage or severe reductions in size (even to the ground level) and in most cases, still grow back. Crepes that are planted north of our area can encounter freeze damage to the top growth, but are like an annual in that they can grow back from their roots. From a pure health prospective, they should be maintained in the same fashion as a shade tree by removing crossing limbs and canes (if practical), removing root sprouts, structural pruning, and basic deadwood removal. This type of pruning can be done anytime of the year and is the most beneficial to the long term health and longevity of the plant

From an aesthetic point of view, tip pruning of Crepes can be utilized to make them more attractive. Proper tip pruning should be accomplished in late January thru March, but not after the new shoots have emerged in the spring. Current research shows that tip pruning (or heavy pruning) at other times of the year, may increase the odds of freeze damage. Tip pruning should be to approximate pencil size twigs and in a rounded form. Some Crepes may end up columnar in shape, but in any event, the top growth should not be cut flat because it encourages all the blooms to be at one height. Severe cutting back is not attractive, reduces food storage, encourages poor branching structure and should be avoided. Since all Crepe Myrtles will have dead tips in the spring, removal of pencil size twigs avoids viewing the dead portion and is more aesthetically pleasing. The best show of flowers can be obtained by constantly removing the spent seed pods (dead heading) throughout the growing season, although it can be very time consuming.

The amount of time (or cost) required to achieve a positive effect is much less for small (or medium) size Crepe Myrtles. Large or tall Crepes can be structurally pruned as noted above, however, tip pruning can be very time consuming (or costly) and is not of much benefit to the overall health. Severely cutting back the trunks will reduce the amount of time (or cost) to maintain them, but it is not what is best for the plants structure or health.

In summary, if you are concerned about only health, prune it like a small shade tree. If you are concerned with the aesthetics, prune it like a small shade tree and also tip prune. If you really want show, prune the seed pods as they die. Each step beyond leaving them alone involves more time and cost. What is right for you depends on your personal preference, the characteristics of the plant, the site and of course, and the budget.

Crepe Myrtle Turning Black

Why are the stems and leaves on my Crepe Myrtles turning black?

Aphids and azalea bark scale feed on the sugars produced by Crepe Myrtles.  The insects’ digestive systems do not process all of the material they eat. The undigested sugars pass through the insects and are deposited on the leaf or stem where the insects are feeding.   This excretion is called honeydew. Honeydew has a high sugar content and is sticky to the touch.  Honeydew is a perfect medium for the growth of black sooty mold.  This black mold is what you are seeing on the twigs and limbs of Crepe Myrtles.  To eliminate the black sooty mold, it is necessary to stop the production of honeydew.  To eliminate the honeydew it is necessary to manage the insects producing it.  Azalea bark scale can be managed with appropriately timed applications of horticultural oil .  We are also experiencing great results managing aphids, azalea bark scale, and thus sooty mold, with the systemic insecticide, Merit®.  A single soil injection application between late winter and early spring provides a year’s management.  The Crepe Myrtles also benefit from the soil injection process, which includes fertilization and soil aeration. Your arborist can design a management program that best meets your needs.

by Chris Brewer – I.S.A. Certified Arborist

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