Extension Agent: “Wet conditions can harm Camellias”
By: Bobby Smith
The following is a news column first published by a fellow County Agent, Charles Phillips, who just retired from Cooperative Extension in Columbia County. I have been seeing these same problems in our area.
As I look out the window, I see rain beginning to fall, again.
We have been blessed with a surplus of rain, and we hope that it will continue during the summer months. Rain is beneficial to plants, but too much can cause problems.
Excessive rain can damage camellias, which are blooming now and will be putting on new growth when the weather warms up. There are three major diseases of camellias—camellia dieback and canker, flower blight and root rot. Also, there are secondary diseases such as edema and algal leaf spot.
Camellia dieback and canker will cause the leaves on affected branches to suddenly turn yellow and wilt. Then, the branch tips usually die and gray blotches appear on the bark and stem.
These blotches will turn into sunken areas, which are cankers, and these cankers will eventually girdle the stem. Parts of the plant above the stem canker lose vigor, wilt and die. This disease will show up more during hot, dry weather.
Camellias should be planted in well-drained soil. They need to be fertilized and pruned properly to reduce the amount of stress on the plant. If your plant is affected by dieback and canker, you need to remove the infected parts of the plant and treat with a fungicide to help protect the plant.
The second major disease is flower blight. This disease causes the flowers to turn brown and drop off. Flower blight likes cool, wet conditions. The first symptoms of the disease are small, irregular shaped spots on the flower petals. These spots enlarge to cover the entire flower within 24 to 48 hours.
If there are small spots on the flower that don't enlarge, these spots could be sun scold or wind damage. The best control of this disease is sanitation. Remove all infected flowers from the plant, and rake up all leaves, flowers and mulch from under the plant. Then put in new mulch.
With all the rain lately, root rot could be a major problem this year. Most root rot is caused by the fungus Phytophthora cinnamomi. The first symptoms of root rot are a uniform leaf yellowing, poor growth and wilting of the entire plant.
The infected root systems lack small feeder roots and appear discolored. Infected roots are a red-brown to dark-brown color. Healthy roots are white.
Death of the plant can occur rapidly, or the plant might remain in a state of decline for several years. The best way to control this disease is to plant in well-drained soil and to watch how much water is applied to the plants.
Another disease that we might see this year because of the wet conditions is edema (sometimes spelled oedema), a disorder of camellia leaves due to excessive water uptake by the roots and a reduced ability of the foliage to transpire this buildup of water.
The symptoms will first appear on the bottom of the leaf as small, water-soaked, raised areas. As the water pressure builds up in the leaf tissue, blisters will form. They will be rust to yellow in color and will show up on the top of the leaf.
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.
Edema can make the plant look bad, but does very little damage. In addition to camellias, this condition occurs on several other landscape plants, such as English ivy, fatshedera, ligustrum, rhododendron and jasmine.
To help control this problem, improve air movement around the plants and increase the level of sunlight by pruning back adjacent plants and overhanging tree limbs. Also, watch how much irrigation water is being applied.
The last disease problem is Algal leaf spot, a common disease on both camellias and magnolias. These leaf spots can be green, brown, reddish or tan, and occur on the top of the leaf. Camellias that receive more sunlight are more prone to being infected with algal leaf spot. Other conditions that increase the chance or severity of infection are poor air circulation and excessive leaf wetness through rainfall or irrigation.
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 can reduce the amount of algal leaf spot. Fungicides are not the answer if the growing conditions of the plant are not improved. If a fungicide is used, it should contain copper.
For information on Camellia’s and other ornamental plants contact your local UGA Cooperative Extension office at 1 800 ASKUGA1 or 1 800 275 8421.