Magnolia, Southern Magnolia Magnolia grandiflora Propagation Magnolias are usually propagated by semi-hardwood stem tip cuttings taken in the summer. Rooting should occur in 9 weeks with IBA Quick Dip 12000 PPM, intermittent mist, and soil temperatures of 75-80 degrees F. Pests and Diseases The current Insect Management Guide for Commercial Foliage and Woody Ornamentals can be found at http://edis.ifas.ufl.edu/ig012. The current Professional Disease Management Guide for Ornamental Plants can be found at http://edis.ifas.ufl.edu/pp123. Black twig borer (Xylosandrus compactus) Recognition: Twig dieback in otherwise healthy trees is conspicuous. The twigs will eventually break off and fall to the ground. Tiny entrance holes may be found on undersides of affected twigs, where the female insect has bored holes in which to lay her eggs. The white grub-like larvae feed and pupate inside the twig. Contributing factors: none Management recommendations: Prune out and destroy infested twigs. The problem is primarily aesthetic. Magnolia white scale (Pseudaulacaspis cockerelli) Recognition: Adults are pear-shaped, shiny white armored scales with yellowish brown bodies underneath the armor. The stationary adults may be clustered along the midrib on the undersides of leaves, or scattered on both leaf surfaces. Feeding damage results in yellow spots on the leaves. Eggs are laid underneath the armor, and newly hatched crawlers (small yellow ovals) emerge which move along the leaves and twigs. They are tiny and require a hand lens to detect. Contributing factors: Scales are present year 1
round, but large numbers of eggs and crawlers are present in the early spring. Management recommendations: On established trees, the problem is primarily aesthetic rather than damaging to the tree. Mature scales are difficult to control. Round holes in the scale bodies indicate parasitic wasps have emerged and are helping control the pest population. Contact insecticides should be timed to control crawlers, since matures are well-protected by a waxy covering. Systemic insecticides may be needed for severe infestations. Dead scales will still remain on the plant, however. Magnified Scale Insect Magnolia Root Borer (Euzophera magnolialis) Recognition: Plants may first be seen to generally decline, as seen to the left. The decline is caused by reduced root function and partial girdling of the tree by larval feeding. Symptom severity depends on numbers. The insect itself is often difficult to find. The larvae feed on the roots, and then crawl to the crown area where they tunnel under the bark. They pupate just under the bark and adults emerge. There are approximately two flights per year, but there may be more in warm pots. The adults oviposit in the bark, when the eggs hatch the larvae head straight for the roots, moving up to the crown as they mature and prepare to pupate. Contributing factors: The magnolia root borer attacks the roots of stressed trees (potted trees are often stressed), and causes a general decline. High fertilization and irrigation rates in nurseries may allow adventitious roots to mask the damage symptoms, but once in the landscape these root systems are shallow and structurally poor. Management recommendations: There is little documentation about this insect and the adult is difficult to find. Root and crown drenches with a systemic insecticide or beneficial nematodes may provide some control. Adult Magnolia Root Borer Magnolia Root Borer larvae and root feeding damage Magnolia Root Borer Larvae 2
Magnolia root borer late-stage larval damage (barked scraped) Adventitious root growth following root borer damage Tuliptree Scale (Toumeyella liriodendri) Recognition: Adult females are ¼ - ½ inch in diameter, hemispherical dark brown, some with yellowish markings. The stationary females are clustered along twigs. Males are grayish ovals and congregate on the backs of leaves. Sooty mold growing on the scale excretia is often the first symptom noticed, since the Tuliptree Scale adults scales blend in with the twigs so well. The scales bear live young underneath the armor, and crawlers (small ovals) emerge and move along the leaves and twigs. In more northern areas they have one generation per year, but in Central Florida they appear to have more. Contributing factors: Scales are present year round, but large numbers of eggs and crawlers are present in the early spring. Management recommendations: This scale can kill small trees and significantly reduce vigor of larger established trees. Horticultural oils may be used, but will require repeated applications. Contact insecticides should be timed to control crawlers, since matures are well-protected by a waxy covering. Systemic insecticides like dinotefuran are needed for severe infestations. Dead scales will still remain on the plant, however. Sooty Mold Tuliptree Scale males 3
Algal leaf spot (Cephaleurus virescens) Scouting Procedure for Magnolia: Recognition: Silvery-grey, green or tan, raised spots or blotches with green margins on leaves are caused by algal leaf spot. Heavily infected plants may experience premature yellowing and leaf loss. Contributing factors: Abundant moisture, high temperature and direct sunlight favor infection. It seems to be most damaging on slow-growing, weakened plants. Management recommendations: Use selective pruning to increase air circulation and remove heavily infected leaves. No fungicides are recommended. Choose 2-3 trees to monitor. Sample 5 (if heavily infested) to 10 (lightly infested) leaves per plant and count mature scales. Count or estimate crawlers. Turn over the armor on a few scales on each leaf and record the presence of eggs using a hand lens. Double stick tape method for crawler detection: as an alternative to counting crawlers on leaves, put double-stick tape around 2 branches on each plant. Count the number of crawlers on the tape. Change tapes weekly. Sail traps can be pinned to a leaf on each tree to detect male adults, which precede crawler emergence by about two weeks. Count the number of adult males on sail traps each week. Sources 1. Knox, G. 1994. Magnolias. University of Florida Extension bulletin CIR1089. http://edis.ifas.ufl.edu/mg270 2. Leibee, G. 1992. Unearthing a Magnolia Menace. American Nurseryman, Jan.15, 1992, p. 70. 3. Leibee, G. 2007. Personal communication and photos of Magnolia root borer. 4. Neal, Cathy, Celeste White and Eleanor Foerste. Key Plant and Key Pests in Central Florida Landscapes. University of Florida Extension slide set. 5. University of Florida Landscape Plant Propagation Information. http://hort.ufl.edu/lppi/ Prepared by: Juanita Popenoe, PhD, Commercial Horticulture Lake County Extension, 1951 Woodlea Rd., Tavares, FL 32778-4052 Tel.: (352) 343-4101, FAX: (352) 343-2767. May 2010. The Institute of Food and Agricultural Science (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. DEPARTMENT OF AGRICULTURE, COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, IFAS, FLORIDA A. & M. UNIVERSITY COOPERATIVE EXTENSION PROGRAM, AND BOARDS OF COUNTY COMMISSIONERS COOPERATING. 4
5