Landscape Architect Articles

LSMP Tree Care September 200409-01-04 | News

Tree Protectors

By Richard Bailey, Tree Pro

The characteristic symptom of frost crack is a long vertical crack down the main trunk of the tree. Frost crack is caused by drastic changes in winter temperature. Uneven contraction of the wood causes the trunk to crack. Once a frost crack has occurred it is likely to occur again. A callus forms, but generally the damage is only cosmetic.

Planting trees can be a losing proposition if not done properly. Transplant stress, lack of water and less-than-ideal soil can add up to losses that can impact your bottom line. The costs of replacing dead trees can quickly spoil a project. Using tree protectors and applying mycorrhizae, other bio-stimulants and fertilizer will go a long way toward keeping tree-planting projects profitable.

The good that tree protectors do has been well established. Many studies and countless applications attest to their ability to protect trees from deer, provide accelerated growth, preserve moisture during times of drought, etc. The problem arises from the fact that not all protectors perform these functions equally. Some do the job better than others and some actually harm or even kill the trees.

Tree protectors are designed to protect trees from deer browse and rub, rodents, wind, drought, winter crack, sun scald, mowers, weed-eaters and herbicides. While most protectors perform these functions adequately, they sometimes cause new problems in the process of solving the original ones. Tree protectors that are light in color with adequate ventilation holes are more effective in eliminating these additional problems while still performing their vital protective function.

The first problem caused by tree protectors is rodent infestation. Research shows almost four times as many trees (21.4 percent) protected by dark, unventilated shelters died from vole infestation than did trees protected by light colored, ventilated protectors (5.1 percent)

A tree farmer in Pennsylvania found only one lonely mouse in the 80 lighter colored tubes he installed. But in the other protectors he installed, he found between 50 and 60 percent were infested with mice and many of those had numerous mice–large families of mice, in fact.

It is generally felt that the higher incidence of rodent infestation has to do with the cozier environment provided by dark protectors without ventilation holes. They provide a cozier, warmer home for mice and other creatures. Moreover, manufacturers of these protectors recommend they be pressed down into the ground when they’re installed and that causes reduced airflow inside. Mice, of course, don’t like drafty homes any more than we do.

The second problem is excessive growth rate. Although a more rapid growth rate is generally a good thing, rapid vertical growth, without commensurate diameter growth, produces a stem that is often too thin to support the crown. However, Tree Pro protectors provide for caliper or diameter growth, which is essential if the trees are to be prevented from bowing to the weight of an oversize crown. During a study lasting from 1996 to 2002, Purdue University of West Lafayette, Indiana, found the shelter with the lightest color produced a 35 percent improvement of diameter growth over the shelter with the darkest color.

During winter when deer don?EUR??,,????'???t have enough green leafy materials to eat, they start to strip bark from trees. They also rub against trees and both activities damage bark and leave it vulnerable.

The third problem is heat retention. Tree protectors create a “mini-greenhouse” inside the tube. Both temperature and humidity are generally higher on the inside than on the outside. For years, many of us believed this was beneficial to the tree, and under ideal circumstances it is. However, conditions are seldom ideal. Under real-world conditions some tree protectors cause heat to increase inside the protector to such an extent that the tree is harmed and sometimes even destroyed.

A “closed” system (i.e., one in which the only air circulating into the protector is through the opening at the top) is not healthy for the tree. For photosynthesis to take place at an optimal rate, there must be a ready supply of “fresh” air. A closed system also promotes the retention of heat and moisture inside the protector. In direct winter sunlight, over a period of days, it can get warm enough inside dark protectors for the trees to come out of dormancy prematurely. That often results in death and dieback when the temperature drops again.

The reverse happens in the fall when the trees are supposed to go dormant. Some protectors (again, usually the nonvented kind with darker, less translucent colors) retain heat, which delays the trees from going dormant. As a result, when the outside temperature drops into the low 20s, dieback and worse often occur because the trees haven’t hardened off.

Because Tree Pro protectors are lighter in color, they absorb less heat from the sun. In addition, the vented type of Tree Pro protector allows fresh, cool air to circulate into the protector. As a result the dieback and death that other protectors cause are virtually nonexistent.

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Fall Applications of Microinjection Treatments

By Terry A. Tattar, Ph.D., Professor,
Shade Tree Laboratory, Department of Microbiology,
University of Massachusetts, Amherst, MA 01003

Microinjection treatments can be applied to tree health problems in the fall and early winter.

Fall is a time when many tree health problems can be effectively treated. As trees in temperate climates and subtropical climates go into dormancy many plant pathogens and insect pests continue to be active. In some cases, fall treatments lower pest and pathogen populations and give trees protection against health problems in the following spring. In addition, the root growth without shoot growth that occurs in the fall facilitates treatments of nutrient abnormalities at this time.

A trees vascular system remains active until the soil temperatures drop below 40 degrees F (5 degrees C). Materials injected into the tree during the fall will move both upward into the branches and downward into the roots. The amount of sap movement is less in the fall compared to the spring and summer when large amounts of water are lost through the leaves during transpiration. Sap movement, however, in the fall is very similar to that in spring and summer.

The following 4 examples are common tree health problems that can be treated in the coming fall months by microinjection technology:

Leaf scorch diseases of hardwood trees – The pathogen over-winters in high populations in the roots. Symptom remission can be achieved by microinjection of oxytetracycline antibiotics in the fall. The antibiotic treatment, however, does not eradicate the bacteria, and treatments have to be repeated every one to two years to keep the infected tree in remission.
Adelgids on coniferous hosts – This insect is most active in cool weather and can be effectively eradicated by microinjection of Imicide??????oe*(imadacloprid) insecticide which has been shown to be extremely stable within plant tissues and often provides protection for one year after injection. Microinjection capsules are placed onto the hemlock trees in the early fall which helps eradicate the existing adelgids and prevent reinfestation during the next spring and summer seasons.
Anthracnose diseases of hardwood trees – Fall microinjection of fungicides can provide protection for recently formed twigs and buds and may help to improve to overall appearance of the trees during the spring growing season.
Nutrient abnormalities on all trees – Mineral nutrient deficiencies cause health problems, such as chlorosis, on many species of trees. A soil or tissue test is often needed to confirm the exact nature and severity of the deficiency. Many of these mineral deficiencies, such as iron deficiency and manganese deficiency, can be corrected by microinjection during the fall season because the root system is actively growing at this time. Minerals are quite stable in the tree and are available to be transported during the next spring and summer growing season. In some urban locations, the soil surface is covered with asphalt, bricks, cement or a wood deck, and microinjection provides the only practical approach to the application of mineral treatments.

For more information contact: tattar@microbio.umass.edu. *Imicide is a registered trade mark of the J. J. Mauget Company.

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Effects of Cold Temperatures on Trees and Plants

By Ron Kujawski, University of Massachussetts
Extension, Landscape, Nursery and Urban Forestry Program

Un-mulched fall planted trees and shrubs are most susceptible to injury from frost heaves because of the absence of extensive anchoring roots.

Sunscald occurs when the trunk is heated up in the late afternoon sun and that warms up the cells that were protectively hardened off for the winter months. The rapid evening drop in temperature then kills those cells. The trunk can be wrapped in a white tree wrap such as heavy kraft paper or burlap. This doesn?EUR??,,????'???t insulate the tree, however, it helps reflect light. Wrap the trunk from the soil line to the lowest branch in the fall and remove the wrap in the spring.

Once frozen, soil temperature remains fairly constant at least at depths greater than six inches. If low temperatures affect roots, it is the feeder roots nearest the surface that will be killed. It may be that the greatest damage to roots is a result of frost heaves that break the roots apart. One type of cold injury that is most certain is the killing of flower buds on those trees and shrubs that are marginally healthy. Flower buds are typically less hardy than leaf buds. Buds, however, are not the only structures where hardiness differences exist. In mid-winter, living xylem tissue tends to be less hardy than cambium and phloem tissue. It is the xylem in smaller branches that is most prone to damage. Affected branches will be to slow to leaf and flower in spring, or they may die. The xylem of cold damaged branches will appear to be black or darkened. Cold injury such as sun scald and frost cracks often occurs in response to sudden or wide fluctuations in the temperature of the wood. The temperature of the wood may differ as much as 18 degrees from the air temperature on sunny days. On cold days when the sun warms the sunny side of the trunk to a temperature above freezing some expansion of the wood will occur.

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Rules for Freeze Damage to Citrus Trees

By L.K. Jackson, D.P.H. Tucker and T.R. Fasulo,
University of Florida, Institute of Food and Agricultural Sciences

Damaged trees that sweat in the bank or wrap may be attacked by a fungus that can quickly damage or kill them.

Tree damage at the time of a freeze is probably the most important factor influencing the susceptibility of citrus to freezing temperatures. Citrus trees are evergreens that never become fully dormant and therefore cannot withstand temperatures as low as those tolerated by deciduous trees. Cold weather preconditioning induces a degree of dormancy in citrus, but only if the preconditioning comes gradually. Trees in active growth are more severely injured by cold than those that are somewhat dormant. One of the best ways to lessen cold injury and hasten recovery from cold damage is to maintain healthy trees. Follow cultural practices that will induce dormancy in early winter and try to maintain this dormancy until all cold weather has passed.

Rules for the care of cold damaged citrus trees depend on the time of year the injury occurred, the condition of the trees at the time of injury and weather conditions immediately following. The natural reaction is to do something right away, however, there is actually very little that can be done at that time since it is impossible to determine the full extent of the injury. Twigs and branches may continue to die for several months and for up to two years following a severe freeze. They should receive extra care, however a ?EUR??,,????'??wait and see?EUR??,,????'?? attitude is best.

If damage is slight and there are some leaves and green twigs above the bank or wrap, no special steps need to be taken. These trees have enough living wood to develop new tops. Even so, the banks and wraps should be removed to make sure the bark is firm. This should be repeated every week. Trees that were not banked at the time of the freeze should not be banked until the next forecast of freezing temperatures.