Garden Tips Newsletter
July 6, 2009
Azaleas
Yellow foliage is a common sight on azaleas throughout Mississippi, but the cause of the problem may vary. Azaleas grow best in acid soil, that is, with a pH of 4.5 to 6.0. If you live in an area where the pH is 7.0 or higher, your azaleas may have an iron deficiency, indicated by yellow leaves with green veins.
Even though adequate iron may be in the soil, it is unavailable to the plant roots. Lower the pH of the soil by applying acid-forming fertilizers, such as those formulated for azaleas and camellias. You can also treat the soil with aluminum sulfate or lime sulfur.
For quicker but temporary results, spray the foliage with iron chelate. If the foliage is stippled with yellow, the damage is probably due to the feeding of lace bugs or spider mites. Spray with insecticidal soap, and follow label directions carefully. For complete control measures of lacebugs and spider mites, look for the publication 2369, Insect Pests of Perennial Plants in the Home Landscape online or you can request one of these publications through your county Extension office.
Crape Myrtles
Lack of sunlight will affect bloom production in crepe myrtles. In addition, infestation of aphids may lead to poor flowering. Honeydew left behind by the aphids invites sooty mold on leaves. This black coating, in turn, interferes with photosynthesis, which reduces the plant's vigor. Sooty mold can be prevented by controlling the aphids. Spray with insecticidal soap according to label directions. Refer to the same publication mentioned above for more complete control measures of aphids.
Lelia Scott Kelly, Ph.D., writes Garden Tips weekly and is a Horticulture Specialist with the Mississippi State University Extension Service. Her office is in the North Mississippi Research & Extension Center, Verona.