When you think of all that trees provide us — oxygen, shade, beauty and shelter — it makes sense for grounds care professionals to do as much as they can to protect them from harm. However, if you are not able to check the trees under your care everyday, you need to enlist the help of your clients and teach them how to care for the trees on their property.
One way to teach employees, property managers and homeowners how to reduce and control disease activity is through the tree disease triangle. This triangle clearly illustrates how to break the disease cycle with sound horticultural practices or pathogen removal.
The presence of all three triangle criteria mean that a disease can develop. On one side of the triangle is the tree and its susceptibility to a particular pathogen. That pathogen forms side two of the triangle. The third side is the specific environment or cultural condition at the site. The host tree, pathogen and environment join forces to create a problem. By breaking a side of the triangle, the chances are greatly increased for disease control.
Before you begin to council clients on tree selection, take advantage of information from nurseries and agricultural extension services about disease-resistant plants. Consider the specific diseases a plant can tolerate in relationship to the site in which it will be planted. Suggest specific varieties of trees compatible with the planting site and give customers Web site addresses, names and phone numbers of tree information resources.
Selecting the right tree for the right location is critical to the survival of that tree. For example, if your clients want to add a Cotoneaster to their property, make sure they understand that fire blight will threaten the Cotoneaster because of nearby ailing pear trees. Instruct customers that planting Douglas Firs on slopes promotes air circulation. Tell property owners why a Hemlock won't grow well in their wet, alkaline soil. Help customers choose a disease-resistant Juniper. Customers can then choose to change locations, change species or alter threatening conditions such as excessive shade or type of irrigation.
In order to ensure the tree has a fighting chance, give customers the benefit of professional experience by planting the tree properly. The skimpy planting instructions on shipping tags are insufficient for the best possible start.
Help property owners create a good growing environment for their trees. Give them information on all aspects of tree care including pruning, leaf raking, watering, mulching, fertilizing, plant compatibility, aerating, cone removal and weed control. Unless you handle every aspect of their tree care, your clients likely will neglect or mishandle these chores.
To battle tree diseases, you need to find out about fungal, viral and bacteria pathogens. Understand how they are introduced into landscapes by insects, rain, wind, soil, mulch and plants. Learn about the types of pathogens that affect specific species. It might also help to know the difference between leaf blight on arborvitae caused by Cercospora and twig blight on pines caused by Sphaeropsis sapinea.
Compare healthy leaves to those with spots, holes or other signs of stress. It is important to know that a sycamore with anthracnose has browned edges on the leaves as they expand and that juniper tip blight begins on recent growth of the lower branches. Know that cherry trees in the early stages of black knot have small swellings on the current or last season's growth.
Check trees regularly for signs of pathogens or diseases. Routinely look for signs of stress and help clients learn to identify problems, as well. Provide customers with simple guidelines to help them identify specific symptoms, so that if problems occur, early intervention is possible.
There are a variety of treatments for tree diseases. Pruning affected twigs and destroying them may be more effective than applying a fungicide. Watering from below rather than applying top irrigation may reduce blight on junipers.
In some cases, no treatment is the best remedy, especially when a disease is simply aesthetically unappealing and not life threatening to the tree. It also can become too late in the growing season for a treatment to be effective.
The pathogen side of the triangle is the hardest to break because complete removal of a pathogen is nearly impossible.
There are specific growing conditions in which pathogens thrive. Know which pathogens increase in wet conditions and find out how drought affects pathogens. Also, understand how shade promotes specific diseases when combined with excessive rain and determine which type of irrigation will work best for a specific type of plant. Recognize the effects of overcrowding and the need for increased air circulation.
By thinning plants out, you might reduce powdery mildew. Another example would be to irrigate in the early morning to give plants the change needed to fight disease.
When it's time to renew annual agreements or solicit new customers, emphasize tree health through horticultural practices. Show customers how to properly care for their trees and that proper pruning, raking, fertilizing and mulching are the best disease prevention.
Sometimes it is necessary to actually remove a tree to promote air circulation and healthy growth. Provide customers with brochures, fact sheets and other information from reliable sources that reinforce these recommendations.
Inspect trees carefully in spring. If plants have been neglected, then contact customers before treatment. Ask customers to first try horticultural remedies. Explain again that chemical treatments may not work if the tree isn't cared for properly. Emphasize the cooperative nature required between contractors and customers to insure healthy trees.
If chemical treatment becomes necessary, explain again that chemicals may help trees only to fight disease rather than completely eliminate it. Use a printed notice prior to treatment to reinforce this point.
If trees continue to suffer after treatment, then customers will have known in advance of that possibility. Their expectations will be more reasonable and they will be less likely to hold you responsible for failing to cure the disease.
Rich Nelson is a certified tree arborist and the division manager of tree and shrub care for One Step Tree & Lawn Care (Rochester, N.Y.).