Sign of spring
Published 12:42 pm Wednesday, April 4, 2007
By By LYDIA GRIMES – features writer
This year the dogwood trees in many areas are beautiful. As I ride the streets, I notice that even trees in sites that dogwoods are normally considered to be poor adapted, the dogwoods are really showing off. Dogwoods are native and have been a mainstay of our southern landscapes for a long time. However, recently many people have been reluctant to add new plantings to the landscape. This is unfortunate, but I understand that they have become more difficult to grow in recent years. The problems with this tree can be traced to a few sources; site selection, fertility, insect damage, and disease pressure are some of them. The good news is that these problems can be successfully managed.
Dogwood naturally grows in the under story of other trees. In our area, it is typically pine trees. The pine trees allow some sun light to penetrate, but protect the dogwood foliage from direct sunlight. Auburn University researchers have noticed that dogwoods grown under 50 percent shade cloth have more and larger blooms. In the first few years, trees in full sun have full sized blooms for the particular cultivar. In subsequent years, the number and size of blooms drops in full sun when compared to shade protected plants. Additionally, dogwoods grown in shade have a higher survival rate and the surviving plants are thriftier.
A few years ago, Extension Plant Pathologist Austin Hagan, noticed that dogwood samples coming into the plant diagnostic lab at Auburn University were often coming from landscape companies that had planted the plants, cared for them for a year, and guaranteed them to survive.
When the people submitting the samples were questioned, a pattern of treatment emerged.
The trees were planted in home lawns and fertilized to encourage them to grow quickly.
Additionally, the home lawns were being fertilized to make the grass grow lush and green. Survival of young dogwood trees in this regime was very low.
The cause for this low survival rate is thought to be a combination of increased disease pressure and an imbalance in the canopy and the root system of the tree.
Regardless, the take home message is to be careful not to use too much high nitrogen fertilizer, when the tree is young.
Dogwood borer is an insect species that can be devastating to dogwoods, especially if the bark of the tree is nicked or wounded by lawn care equipment. Borers are also worse in trees that are planted in full sun.
Therefore, wounded trees and those in full sun may warrant more aggressive management. In this case, aggressive management means timely sprays with an insecticide.
The insect is active in the spring of the year and can be controlled with a series of sprays using the insecticide permethrin.
In the Escambia County area, the trunk and scaffold limbs of the tree should be sprayed in mid March, mid April and again in mid May to control the dogwood borer.
Dogwood diseases usually are not as devastating as the dogwood borer.
However, timely disease control can really extend the time that leaves stay on the trees in the fall.
This has at least two benefits.
First, the leaves produce the food for the plant, and the longer they stay on, the more likely the tree is to remain healthy.
Second, dogwoods have surprisingly good fall color.
This is often lost because the leaves are rarely held long enough to demonstrate fall color.
The diseases include mildews, and various leaf spots. To mitigate foliar disease problems, the plant foliage can be sprayed with two sprays of a fungicide such as dachonil in late May and again two weeks later.
As with most plants, it is best to plant in an adapted area. In many cases, dogwoods have thrived with little or no care.
However, the cultural practices that we use are important. In the case of dogwoods, homeowners should be careful not to over fertilize new plantings, and watch for insect and disease problems.
For more information on dogwoods is available at the local extension office (251) 867-7760 or on the web at www.aces.edu. I recommend ANR-551 Dogwood Diseases in Alabama, ANR-1077 Selection and Care of Dogwoods.
The University of Georgia has some good information on the Dogwood borer at www.caes.uga.edu/department/ent/lpm/ornamentals/dogwoodborer.html.