ACES Publications

Author: Jacqueline Mullen, Austin Hagan
PubID: ANR-0943
Title: Algal Leaf Spot
Pages: NA     Balance: 0

ANR-943, Web Only, Revised Nov 2003

Jacqueline Mullen, Extension Plant Pathologist and Diagnostician, and Austin Hagan, Extension Plant Pathologist, Professor, Entomology and Plant Pathology, both with Auburn University

Algal Leaf Spot

Algal leaf spot on magnolia

Algal leaf spot, caused by the alga Cephaleuros virescens, may appear on a wide variety of plant species. In Alabama, southern magnolia and camellia trees are the most common targets of algal leaf spot problems. The list of plants susceptible to C. virescens also includes apple, aucuba, azalea, blueberry, bougainvillea, boxwood, cleyera, crape myrtle, fig, gardenia, holly, Indian hawthorn, jasmine, juniper, leucothoe, magnolia, oak, orchid (Cattleya), pecan, philodendron, photinia, privet, pyracantha, rhododendron, schefflera, sycamore, viburnum, and wisteria.

Symptoms. Leaf spots develop as pale green or pale red, rough, superficial, netlike circular spots with wavy or feathered margins. In some situations and on some hosts, the alga may infect twigs and branches, causing girdling lesions. Algal infections of twigs often cause superficial cell layers to become slightly swollen and cracked; this cracking will cause the twigs to be more susceptible to fungal infection. When sporangia (algal spore structures) are produced, the lesions become reddish. When sporangia are not produced, the spots remain light green in color.

Persistence and Transmission. Disease spread is favored by frequent rains. During wet weather, spores are spread by water droplets or wind-driven rain to leaves or twigs which are then colonized by the alga. Cephaleuros virescens will survive adverse conditions in spots on leaves and twigs. Weakened trees or plants are most susceptible to attack.

Control. Algal leaf spot can be controlled by the following strategies:

’ΔΆ Use good sanitation practices for control in most home landscapes.

’ΔΆ Hand remove spotted leaves on lightly diseased plants. Collect and discard or destroy all fallen leaves. You can discard leaves with trash, burn them, or add them to a hot, properly maintained compost pile.

’ΔΆ Prune overhanging trees around diseased plants to help lower humidity levels and speed the drying of leaf surfaces.

’ΔΆ Improve soil drainage if this is a problem.

’ΔΆ Apply Bordeaux mixture
(8 tablespoons per gallon) as protective sprays on heavily spotted camellia and southern magnolia. Always follow the directions on the label. Repeat spray treatments every 2 weeks if cool wet weather persists.

Use chemicals only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee and product and does not recommend one product instead of another that might be similar.

For more information, call your county Extension office. Look in your telephone directory under your county's name to find the number.

Issued in furtherance of Cooperative Extension work in agriculture and home economics, Acts of May 8 and June 30, 1914, and other related acts, in cooperation with the U.S. Department of Agriculture. The Alabama Cooperative Extension System (Alabama A&M University and Auburn University) offers educational programs, materials, and equal opportunity employment to all people without regard to race, color, national origin, religion, sex, age, veteran status, or disability.

© 2003 by the Alabama Cooperative Extension System. All rights reserved.

For more information, contact your county Extension office. Visit or look in your telephone directory under your county's name to find contact information.

Published by the Alabama Cooperative Extension System (Alabama A&M University and Auburn University), an equal opportunity educator and employer.

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