With the warmer weather of spring, eggs laid by adult defoliating insects have started to hatch. Caterpillar larvae will begin feeding on leaves and tender parts of the plant. The resulting defoliation is unsightly and can greatly reduce photosynthesis, thereby reducing the energy a tree has to grow, thrive and defend itself against insect and disease pathogens.
Most deciduous species are at risk especially if trees are stressed by weather, poor soil conditions or other factors. One of the best things you can do is simply to keep your trees healthy with regular maintenance including proper irrigation and mulch, fertilization, and removal of dead wood. Healthy trees are better able to withstand an infestation.
Once damage is apparent it is often too late to provide effective treatments for optimal protection. With this in mind, trees should be inspected for signs of an infestation in early spring.
Mulching is a great practice to keep trees healthy. It eliminates competition between tree roots and turf as well as conserving soil moisture and moderating soil temperature.
Ideally, mulch should be applied beneath the entire canopy, but smaller mulched areas are acceptable. Depth should not exceed four inches and two inches is adequate on shallow rooted shrubs and perennials. Mulch beds do not have to be round or symmetrical. Shrubs and perennials can be planted within the mulch areas, but solid masses of ground covers should be avoided where optimum tree growth is desired.
The biggest mistake people make when mulching is piling it against stems of trees and shrubs. Mulch “mountains” and “mulch volcanoes” are so common in some regions that homeowners and some professionals think this is acceptable and even desirable. Stem tissues are not intended to remain constantly moist from mulch accumulation. Insect and disease infestations, as well as stem girdling roots, often develop on trees with excessive mulching.
Plant leaves manufacture sugar and carbohydrates that are the basic food or energy source for all plant processes – growth, root development and flower and seed production. Leaves also provide indirect benefits such as emitting oxygen, screening out air pollutants, shading the ground to moderate surface temperatures and intercepting precipitation to minimize erosion.
Defoliation, or loss of leaves, eliminates food production capability. This weakens the tree, reduces growth and results in pale leaves and branch dieback. Effects can range from a slight reduction in vigor to total death in severe cases.
When defoliation occurs early in the growing season just as leaves reach full expansion, it is most detrimental. At this time, considerable energy has been expended in leaf development but food reserves are not yet replenished. In spring, the tree is further weakened as it expends additional energy in refoliation.
Trees that receive regular care including pruning, fertilization, mulching and watering during dry periods are better able to tolerate defoliation. If a tree is defoliated, watering during dry periods is recommended to aid the refoliation process. Fertilization can also help encourage refoliation and replenish nutrients.
YOUNG TREE CARE
The highest tree loss rates in a landscape are within the first three years of planting while the root system grows from the root ball into your soil. Many of these losses are preventable with the proper care of newly transplanted, young trees.
Applying water at the right time, and in the right way, is the first step. Water should be applied to both the original root ball and surrounding soil. This should occur one to two times per week during dry periods, depending on the weather and soil moisture levels.
Properly applied mulch will conserve soil moisture and provide a better environment for roots to grow in. Mulch should never be in contact with the trunk of the tree.
Pest management is also important for young trees since they cannot afford to lose many of their leaves or branches to pests. Fertilization can help in establishing healthy growth and is a cost-effective way to help turn small plants into larger ones!
MANAGING DAMAGING TREE INSECTS
Borers, mites, scale and beetles are common tree pests in the late spring and summer. Their presence can result in wilting, thinning of the canopy, premature leaf drop and branch dieback. Many of these insects are not selective, feeding on various types of deciduous and evergreen species.
Treatments including the release of beneficial insects can be very effective for suppressing damaging pests. Examples of natural predators include lady beetles, green lacewings, trichogramma wasps and predaceous mites. When released as part of a managment program, these beneficials help eliminate problematic insects. The first step to proper treatment is correctly identifying the type of infestation. After diagnosis, the best method of treatment can be determined and timed appropriately for maximum effectiveness.
CARING FOR MATURE TREES
By the time a tree has made it to maturity, it is well adapted to the soil and other environmental conditions of its location. It has withstood stresses such as drought, extremes of moisture and windstorms. Often, it has also reached large stature and has become a “feature tree” in the landscape.
But, unfortunately, as a tree gets older, it becomes less able to adapt to major changes and can more easily be pushed into a spiral of decline. Therefore, the key to care of mature trees is to maintain stable conditions – avoiding disturbances to the root system and pruning to preserve structural integrity.
Pruning of mature trees should usually be restricted to dead branches, removing foliage only when necessary. Soil management goals are: (1) to simulate ideal conditions found in nature by mulching as far out to the dripline as possible, (2) fertilizing by prescription to correct nutrient deficiencies and (3) irrigating as needed to avoid drought stress.
Shrubs are routinely pruned to maintain size, remove old branches and stems that do not flower well and to eliminate dead and dying branches. But don't confuse shearing with pruning. These are very different methods that are used to maintain shrubs.
Shearing is usually done with manual or powered hedge shears and removes a portion of only the new growth each year. Shearing usually alters the natural form of the plant resulting in a dense outer crown and a “rigid” formal appearance. Because only a portion of the new growth is removed, sheared plants become larger each year. It is difficult to maintain the size, health and appearance through frequent shearing. Shearing is usually desirable only on hedges and formal shrub gardens. Late summer or fall shearing may result in winter injury.
Pruning removes current and previous season’s growth using hand pruners. Pruning is the desired method of maintaining the size, shape and health of shrubs. By selective thinning, light and air can penetrate the interior crown, which promotes growth inside the plant. This provides a healthier plant with an informal, natural appearance. By pruning new and old growth, the plant can be maintained at a desired size.
Foliar diseases caused by fungi are common this time of year. With this in mind, as leaves appear, it is important to notice anything unusual in the foliage of your trees. Some signs of an issue include:
Discolored or dead “spots” on leaves
Unusual coating on the leaf surface
Browning or yellowing on the outer margins of leaves or along leaf veins
Bumps or pustules on leaves
Loss of needles on conifers
Virtually any tree species can be impacted by foliar diseases. Infected trees can be unsightly, and tree health issues may arise when defoliation, or loss of leaves, occurs. Effective management varies according to the underlying problem so trees with symptoms should be inspected by a certified arborist.
Tree Artisans 3415 Cedarlawn Dr. Colorado Springs, CO 80918 www.treeartisans.com 719.822.6733