Home gardeners planting magnolias and camellias within close proximity of each other are potentially courting damage and plant decline in not one garden species, but two. The fungus disease algal leaf spot targets these two trees above others as hosts, easily spreading from one to the other. Maintain vigorous home garden plants to avoid infection and the widespread injury caused by spread.
Maintain vigorous, healthy trees through consistent care as weakened or stressed trees are much more likely to suffer from fungal infections. For vigorous magnolias, plant in areas that offer full sun to partially shaded conditions as well as well-drained, acid soil with a pH of 5.0 to 6.5. Camellias need protection from full sunlight and prefer well-drained soil high in organic content.
Algal leaf spot is a fungal disease that most often attacks camellias and magnolia trees as hosts, according to the University of Florida Nassau County Extension. Caused by the fungal pathogen Cephaleuros virescens, algal leaf spot prefers wet environments and spreads sporadically during rain when it lands on twigs and leaves, making fungus spread from camellia to magnolia trees easy, particularly when planted in close proximity.
As spores gather and infection develops, light green to light red spots that take on a scratchy texture appear on leaf surfaces. Leaf spot borders appear wispy instead of solid. Leaves are the most common site of symptoms; however, pathogens can infect twigs and branches. Lesions, or areas of dying plant tissue, on twigs results in cracks, and lesions may spread around the circumference of branches. Disease can cause cosmetic damage and diminished health but generally does not cause permanent harm.
Algal leaf spot infects many other hosts aside from camellia and magnolia trees. Gardening with susceptible host plants increases the likelihood of disease transfer within your landscape and a greater need for control. Avoid susceptible plants such as apple, boxwood, gardenia, jasmine, oak, pecan and wisteria, says the Alabama Cooperative Extension System. Additionally, if you choose a susceptible plant, avoid planting another susceptible variety nearby.
Avoid overhead irrigation of magnolias, camellias and other susceptible host plants since algal leaf fungus thrives in wet conditions on leaves and twigs, according to the University of Florida Nassau County Extension.
To control algal leaf spot on magnolia and camellia trees when fungus has spread, prune and destroy any affected plant parts. Remove and destroy fallen plant debris. Sanitize pruning tools between each cut and from one plant to the next to prevent disease transfer. Maintain extremely well-drained soil and apply a Bordeaux mixture fungicide to infected magnolia and camellia trees. Reapply once every two weeks during periods of high moisture and cool temperatures, says the Alabama Cooperative Extension System.