Test Your Knowledge - February

A Test Your Knowledge Unknown
Photograph by Dr. Jean Williams-Woodward, Extension Plant Pathology, University of Georgia

Yes. This is camellia edema.

Edema (sometimes spelled oedema) is a physiological disorder of camellia leaves due to excessive water uptake by the roots and a reduced ability of the foliage to transpire (or give off) this buildup of water. The symptoms of edema will occur primarily on the lower leaf surfaces, and at first appear as small, water-soaked, raised areas.

Edema on lower leaf surface of camellia leaves.
Early stage of edema on lower leaf surface of camellia leaves.
Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, bugwood.org

Eventually as the water pressure builds up in the lower leaf tissue, the blisters will erupt into rust-brown or yellow-brown, corky, wart-like layers of dead ruptured cells that are most characteristic of this disorder.

Edema on lower leaf surface of camellia leaves.
Advanced stage of edema on lower leaf surface of camellia leaves.
Photograph by Dr. Jean Williams-Woodward, Extension Plant Pathology, University of Georgia

Edema typically occurs in late-winter or early spring following wet, cool weather. With the cool temperatures, extended cloudy weather and higher relative humidity, camellia plants will take up much more water than they can transpire. It is important to recognize that this condition, although unattractive on the foliage, does not significantly harm the health of the plant, and no spray control measures are required or effective. In addition to camellia, this condition occurs on several other landscape plants, such as English ivy, fatshedera, ligustrum, rhododendron and jasmine.

Control measures include improved air movement around the plants, and an increased level of sunlight by pruning back adjacent plants and over-hanging tree limbs. If irrigation is being employed, monitor the soil moisture levels so as to not over-water these and other shrubs. Make sure new camellias are planted on well-drained soil, and maintain proper soil fertility through soil testing.

There are diseases and insect pests that make similar symptoms on camellia foliage to edema, and these must be controlled. Tea scales are common on camellias and will infest lower leaf surfaces. These infestations will result in a mass of white and gray scale insects that at first glance may appear like edema. Test by scraping with a fingernail; the scales will come off. Tea scale infestations can kill branches and reduce plant vigor.

Tea scale adults on camellias
Close up of adult tea scales on lower leaf surface of camellia leaf
Clemson University - USDA Cooperative Extension Slide Series, bugwood.org

With a severe infestation of tea scales on camellia foliage, yellow areas will result on the upper leaf surfaces corresponding to the presence of scales on the lower surfaces. Refer to HGIC 2053, Camellia Diseases & Insect Pests for control measures for tea scales.

Symptoms of tea scale damage
Yellowed areas on upper leaf surface corresponding to clusters of scale insect on the lower leaf surface
Clemson University - USDA Cooperative Extension Slide Series, bugwood.org

Algal leaf spot (caused by Cephaleuros virescens) is a common disease on both camellias and magnolias in South Carolina.  These leaf spots may be green, brown, reddish or tan, and occur on the upper leaf surfaces of foliage.

Camellia leaves with algal leaf spot
Camellia foliage with algal leaf spot.
Photograph by Joey Williamson, HGIC, Clemson Extension

Camellias that are grown in sites of higher light levels are more prone to being infected with algal leaf spot. Conditions that increase the chance or severity of infection are: poor air circulation and excessive leaf wetness through rainfall or irrigation.

Control can be achieved by raking and removing fallen, diseased foliage, eliminating or reducing frequency of over-head irrigation, and improving air circulation by pruning back nearby shrubs and over-hanging tree limbs. Sprays with a copper-based fungicide may be required.

A camellia leaf with algal leaf spot
Camellia leaf with algal leaf spot.
Photograph by Holly Thornton, University of Georgia

For proper camellia culture, please see HGIC 1062, Camellia. For more information on these and other diseases and insect pests of camellias, refer to HGIC 2053, Camellia Diseases & Insect Pests.

Joey Williamson, Ph.D.
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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.