Camellia - Pests & Diseases and how to cure them
Camellias are an easy plant to grow in our regions, but like all plants there are certain pests & diseases they are prone to. Read below to learn more about how to diagnose camellia problems, and how to solve them.
Dieback and Canker
This disease is caused by the fungus Glomerella cingulate and is one of the most serious diseases of camellia in the Southeast. Camellia sasanqua is affected more commonly than Camellia japonica. It thrives in warm weather with high humidity. The first symptoms you’ll see are leaves turning yellow and dropping. Branch stems die, and you may find gray splotches on stems and bark. Eventually sunken areas, called cankers, will form on stems.
Preventative measures are the best way to control this disease. Spray with a fungicide, such as Bonide Copper Fungicide, in spring. This will prevent the disease from spreading but will not cure an infected plant. Prune already infected branches several inches below the canker, disinfecting your pruners between each cut. Throw away diseased leaves and branches and rake up any that have fallen on the ground. Do not put in your compost.
As the name suggests, this disease only affects the flowers of a plant, not the leaves or branches. In early spring when the climate is moist, the fungus Ciborinia camelliae causes small brown spots to form on flowers. These spots spread to the center of the flower, eventually covering the whole flower. Soon after, flowers drop. Identification of this disease can be difficult because flower browning can also be caused by sun scorch or freezing temperatures. However, in these cases the flower will typically completely turn brown at once instead of over time.
To control, destroy all infected flowers. Don’t put them in your compost. Since the fungus lives in the soil, remove debris and mulch from under the plant and replace with clean mulch. This is an airborne fungus that can travel up to a mile, so it helps if everyone in the community participates in this. Another option to avoid infection is to choose sasanqua varieties of camellia. Since they bloom earlier than japonicas, they are not affected by the springtime fungus. Finally, if chemical controls are necessary, use a soil drench every two weeks between December and January, such as Bonide Captan Fruit and Ornamental.
The most common root rot that affects camellias is caused by the fungus Phytophthora cinnamomi. Symptoms of the disease are entire leaves yellowing, and in severe cases, the wilting of the entire plant. Identification of root rot can also be seen in the roots, which turn red-brown (instead of white) when infected.
There is no cure for a plant infected with root rot, but preventative measures can be taken. Always plant camellias with good drainage, as the fungus thrives in heavy, badly-drained soils. Use fungicides as a preventative, or consider planting sasanquas, which are resistant to this root rot, over the more susceptible japonicas.
Leaf Gall is most commonly found on sasanqua camellias. During new growth in spring, the fungus Exobasidium camelliae infects new shoots and leaves, which become enlarged and fleshy. These leaves have the appearance of a succulent. Color in the infected leaves fades from light green to a pink, almost white. Eventually, these leaves will rupture, exposing white spores on the underside of leaves, allowing the fungus to spread further the following spring.
To prevent spreading of the disease, it is important to remove infected leaves before the spores are released. Also remove fallen leaves and dispose of in the trash. The fungus thrives in moist environments, so avoid getting leaves wet when watering. The fungus does not typically spread to other camellias in the garden, nor are plants severely damaged from the disease.
Camellia yellow mottle virus
This virus appears as irregular yellow splotches and patterns on leaves. If flowers are infected, they may show white blotches on the petals. The virus does not cause any lasting damage to plant beyond discoloration, and some growers actually propagate plants with the virus to create variegation in the leaves and flowers. There is no cure for the virus. It spreads predominately from propagation of diseased plants.
Algal Leaf Spot
Algal Leaf Spot thrives in wet weather during the summer. The alga, Cephaleuros virescens causes gray-green to green-brown spots, which are slightly raised from the surface, on leaves. If the infection is severe, entire leaves may turn yellow and drop.
To control, remove infected leaves and branches from the plant and around its base and discard. If the plant is growing close amongst other plants, improving air circulation by pruning back around it, may help as well. Apply Bonide Copper Fungicide every two weeks while wet conditions continue.
Aphids typically infect camellias on areas of new growth, which they damage by sucking out the insides of the foliage. A secondary effect of aphids is caused by the secretions the pests produce. These attract ants and create the perfect environment for the growth of sooty mold. Aphids may be controlled by using a hose to spraying aphids off the infected foliage, or with insecticidal soaps. Sooty mold, however must be treated with an insecticide and then wiped off.
Spider Mites are a common, but serious pest of many ornamental plants, including camellia. When infected, leaves appear speckled with a silver or bronze cast. Mites are typically most active during spring and fall when the weather is cool. Some control may be had by spraying the plant with water, but usually chemical controls will be more effective. To prevent damage for the upcoming year, apply a miticide three times in spring, at 7-day intervals.
Scales can cause serious damage to a camellia if not treated. These small insects pierce leaves (and occasionally stems) and suck out the sap. When young, scales are called “crawlers,” but adults are legless. Crawlers find a spot on the leaf, where they pierce the foliage. They then drop off their legs and remain in the same spot for the remainder of their lives. Many will form a hard shell, or “scale” protection over themselves, which makes treating these insects difficult. Systemic insecticides are more efficient for this reason. Natural forms of control include scraping the scale from the leaves or picking infected leaves off the plant and discarding them in the trash. If the infestation is more severe, spray the plant with horticultural oil in spring, when crawlers are active, to maximize efficiency. Repeat this regimen a second time, ten days later.