- Identifying And Fixing Problems With Camellias
- Common Camellia Problems
- Other Problems with Camellias
- Camellia Troubleshooting
- Camellia Diseases & Insect Pests
- Insect Pests
- Other Problems
- Common Pests and Diseases of Camellias
- How to Manage Pests
Identifying And Fixing Problems With Camellias
Even under the best of circumstances, problems with camellias can and do occur. However, learning how to identify and fix common camellia problems before they become an issue is the best solution.
Common Camellia Problems
Several diseases affect camellia plants. The most common include petal blight, canker, leaf gall, root rot and camellia yellow mottle leaf virus.
- Petal blight affects camellia flowers, causing them to turn brown. This fungal disease generally occurs in spring and is usually due to abundant moisture. Petals develop small brown spots that quickly enlarge until the entire bloom has browned. The infected flowers will usually drop within one to two days. Dark brown veins in the petals are a good indication that a camellia plant is suffering from petal blight. Pull off and dispose of infected flowers and treat with a foliar fungicide every one to two weeks.
- Canker disease can be identified by the sudden wilting of branches along with gray colored blotches. The infected bark usually splits open, giving way to pinkish cankers. Branch tips may also die back. Once infected, prune and destroy cankerous branches, cutting several inches below affected area. Planting camellias in well-drained soil usually helps prevent canker. Spraying with fungicide may also help.
- Leaf gall, or Oedema, is often the result of fungus due to overly moist conditions. Leaves become enlarged and fleshy with small greenish-white galls on the undersides. These eventually turn brown or rust colored. Remove affected leaves and spray with fungicide. Reduce watering and when planting camellias, avoid overcrowding.
- Root rot is a fungal disease causing leaf yellowing, poor growth, and wilting followed by imminent death. Rather than healthy white roots, affected plants exhibit brown root systems. Root rot often results from over watering or poor drainage. Prevention is key to avoiding this problem.
- Camellia yellow mottle leaf virus causes irregular yellow patterns or mottling on camellia leaves. Leaves may eventually turn completely yellow. There is no cure for camellia yellow mottle; therefore, prevention is important. As this virus is transmitted through infected stock, make sure camellia plants are obtained only through healthy plants.
Other Problems with Camellias
Other problems affecting camellia plants include pests and physiological disorders such as scale, camellia brown leaf and bud drop.
- Scale bugs are the most serious pest that attacks camellia plants. These tiny insects attach to the undersides of leaves, which may be cottony in nature. Plants may become yellow, have fewer blooms, drop leaves, and even die. Handpicking can alleviate small infestations; however, the use of horticultural oil is often recommended to smother scale and their eggs.
- Camellia brown leaf or sunscald is the result of too much direct sunlight. Scorched or brown leaves on camellia plants do not usually recover. Avoid planting in direct sun. If necessary, transplant to a shadier location.
- Bud drop occurs when plants receive too much or too little water, insufficient light or extreme cold temperatures. They may also suffer from nutrient deficiencies or mite problems. Unopened buds typically drop off plant prior to blooming and may turn brown.
- Sooty mold is common in summer and into fall. Often the result of sucking insects, like aphids and scale, the black coated leaves will eventually drop.
You can’t help but be attracted to the beauty of camellias and other acid loving plants. It makes them one of the most popular plants in New Zealand gardens.
Here is a quick guide to pests and diseases that camellias can be prone to.
These small and easily recognised insects are associated with new growth. May occur on flower buds during autumn or even winter and new growth in spring.
Symptoms: Clusters of insects on young growth
Remedy: Spray with Enspray Oil at 2 weekly intervals
Mites are another insect that can be found under the leaves of camellias as very fine dust like substance.
Symptoms: Leaves yellow (stippled or mottled) and dehydrated in hot dry weather Remedy: Spray with mite killer
This pest invades our gardens in spring and early summer, they use favourable wind currents to cover large distances to spread through our gardens.
Symptoms: Leaves silver and dry. Brown-black specks appear on underside of leaves
Remedy: Spray with Enspray Oil at 2-3 weekly intervals through summer
This unsightly black sticky substance is actually growing on the residue products secreted by aphids and scale.
Symptoms: Black sooty mould on leaves and twigs
Remedy: Spray with Enspray Oil
It is caused by the fungus Exobasidium camelliae. Leaf galls are most often observed during the spring flush of growth.
Symptoms: Developing leaves and flowers are thickened, fleshy and pale green. As the thickenings enlarge, they become white or pink, with powdery appearance during wet weather
Remedy: Remove and burn all infected parts. Spray with Enspray Oil or Mavrik.
Symptoms: Earliest symptom is light brown or whitish coloured circular spots on petals. Spots enlarge to form irregular blotches until whole flower collapses. Petals feel slimy when rubbed between fingers. Diseased flowers dry up and cling to the plant (leaves and stems are not affected)
Remedy: Avoid overhead watering. Pick off diseased flowers. Spray at two weekly intervals with GroSafe Fungus Fighter.
Lack of fertiliser
Symptoms: Leaves yellow and/or develop dark purple tone. Slow, stunted growth
Remedy: Tui Enrich Rose, Camellia, Azalea and Gardenia Controlled Released Fertiliser in late spring after flower finishes and just before new growth starts
Soil too alkaline
Symptoms: Decline in vigour and leaves turn yellow while the veins remain green
Palmers Remedy: Fertilise with Tui Enrich Rose, Camellia, Azalea and Gardenia Controlled Released Fertiliser in late spring after flowering finishes and just before new growth starts. Do NOT use lime.
Camellia Diseases & Insect Pests
Camellia flower blight rapidly turns flowers brown.
Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
Camellias are one of the most desirable and well-adapted plants for Southern gardens. Many of the common problems of sasanqua camellia (Camellia sasanqua, C. hiemalis, and C. vernalis) and the common Japanese camellia (Camellia japonica) can be prevented or minimized by following the proper cultural recommendations.
The three most serious camellia diseases in South Carolina are camellia dieback and canker, flower blight, and root rot. The most important insect pest to watch for is tea scale. More information on successfully growing camellias is available in HGIC 1062, Camellia.
Camellia Dieback & Canker: This is one of the most serious of all camellia diseases and is caused by the fungus Glomerella cingulata. Leaves on affected branches suddenly turn yellow and wilt. Branch tips usually die. Gray blotches appear on the bark and stem, and then sunken areas (cankers) develop, eventually girdling the stem. Parts of the plant above the stem canker lose vigor, wilt, and die. Damaged plants show more symptoms during hot, dry weather.
Prevention & Treatment: Keep camellias as healthy as possible. Plant in a well-drained acidic soil, avoid wounding and fertilize properly. Remove diseased twigs by pruning several inches below the cankered areas. Disinfect pruning tools between all cuts, using a solution of one part household bleach to nine parts water. Fungicides, such as thiophanate-methyl or copper-based fungicides can be applied during wet periods and normal leaf drop periods to protect fresh leaf scars from infection. Apply all chemicals according to directions on the label. See Table 1 for examples of products.
Camellia Flower Blight: This serious disease of camellia causes the flowers to turn brown. Flower blight appears in early spring when moisture is present and is caused by the fungus Ciborinia camelliae. Symptoms begin as small, brown, irregular-shaped spots on the flower petals. These spots quickly enlarge to cover most of the flower. The entire flower turns brown and usually drops within 24 to 48 hours. Only the flowers of the plant are affected.
This disease can be confused with several other problems that can damage camellia flower petals. Slight browning at the edges of the flower petals may be caused by sun or wind. Suspect a disease problem if the brown area rapidly spreads to the center of the flower. Cold temperatures can also cause browning of the flowers. Dark, brown veins in the petals distinguish flower blight from cold injury.
Prevention & Treatment: Sanitation is the best control. Pull off and destroy all infected flowers. Rake up and remove all leaves, flowers, and plant debris that have fallen to the ground. Replace the mulch under the plant. This fungus survives in the soil. Spores of the fungus can be wind-borne for up to a mile. Therefore, best control is achieved when controls are applied to other camellia plants in the landscape.
Fungicide sprays recommended for the flowers include mancozeb. Application of soil drenches, such as mancozeb or captan, around the plant every 2 weeks from late December through January may be helpful in reducing the intensity of disease. See Table 1 for examples of products. Apply all chemicals according to directions on the label.
Root Rot: This fungal disease is caused by Phytophthora cinnamomi. The first symptoms are a uniform leaf yellowing, poor growth, and wilting of the entire plant. 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 may remain in a state of decline for several years. All varieties of common Japanese camellia are susceptible and all varieties of sasanqua camellia are resistant to this root rot.
Prevention & Treatment: This disease is difficult to control once plants are infected, so prevention is very important. In areas where this disease has been a problem, select Camellia sasanqua cultivars for planting or request C. japonica cultivars grafted onto a sasanqua rootstock. Purchase healthy plants that show no signs of wilting or yellowing of the leaves.
The fungus thrives in areas with poor drainage and warm soils. Always choose locations that have good drainage for planting. The drainage of existing areas can be improved by using raised beds. Fungicides can be effective on a preventative basis only, and repeat applications are required. Fungicides containing mefenoxam (Subdue GR) can be applied in the home landscape, but will not cure an infected plant. Due to product cost and for accurate application, homeowners may want to hire a licensed landscaper to apply products containing soil-applied fungicides. Apply all chemicals according to directions on the label.
Camellia leaf gall (Exobasidium camelliae) on Camellia sasanqua.
Joey Williamson, ©2012 HGIC, Clemson Extension
Leaf Gall: This disease is more common on sasanqua varieties of camellia (Camellia sasanqua) than on Japanese camellia (C. japonica). It is caused by the fungus Exobasidium camelliae. Leaf galls are most often observed during the spring flush of growth. New shoots and leaves become enlarged, thickened and fleshy, and appear abnormal. The color of the affected areas turns from light green to nearly white or pink. Later the galls rupture on the undersides of the leaves revealing a whitish mass of spores. The galls eventually harden and become brown. Plants are seldom severely damaged.
Prevention & Treatment: Remove and destroy young galls before the lower leaf surfaces turn white and spores are released, or the disease will be worse the next year. Rake up and remove fallen leaves. Avoid wetting the leaves when watering. Humid, moist, shady conditions favor gall formation. Chemical controls, such as mancozeb, are limited in effectiveness and must be applied before infection occurs. Start sprays at budbreak and continue through the first of June at 7- to 14-day intervals. See Table 1 for examples of products. Apply all chemicals according to directions on the label.
Camellia yellow mottle virus symptoms on Camellia japonica.
Joey Williamson, ©2009 HGIC, Clemson Extension
Viruses: Camellia yellow mottle virus is transmitted by root grafts and propagation of diseased stock. This virus causes irregular, yellow, mottled, or splotchy patterns of various sizes and shapes on the leaves. Some leaves may turn entirely yellow. Irregular white blotches will appear on infected flowers.
Prevention & Treatment: There is no chemical that will cure the virus. Plant only virus-free plants obtained from a reputable garden center.
Algal Leaf Spot: The parasitic alga Cephaleuros virescens is the most common causal agent of algal leaf spot on camellia and other shrubs and trees. Algal leaf spots may be circular or blotchy in shape, and they are slightly raised from the plant surface.
Camellia japonica foliage with algal leaf spot.
Joey Williamson, ©2010 HGIC, Clemson Extension
The edges of the spots may be wavy or feathered. These spots may vary in color from a crusty gray-green to greenish brown. However, in summer when the alga is reproducing, the spots take on a velvety, red-brown appearance due to the production of reddish, spore-producing structures. If colonies are numerous, premature yellowing and loss of leaves can occur. For more information and control measures for alga leaf spot, please see HGIC 2060, Algal Leaf Spot.
Scales: In South Carolina, the most common insect pests of camellia are scales. Scale insects feed on plants by piercing plant tissue and sucking sap. Scales do not look like typical insects. They are small, immobile, and have no visible legs. They vary in appearance depending on species and sex. Some look like small fish scales attached to the plant. As a result of their unusual appearance, populations can reach damaging levels before they are noticed.
Tea scale (Fiorinia theae) damage to top of camellia leaf.
Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
On camellia, scales usually attach to leaves but some species also attach to stems. Their feeding weakens the plant. With a heavy infestation, symptoms include yellowing of the upper leaf surface, fewer and smaller blossoms, leaf drop, twig dieback, and sometimes plant death.
Tea scale (Fiorinia theae) is the most serious scale insect on camellia. This scale attaches to feed on the underside of leaves. Tea scale has an oblong shape with a ridge down the center parallel to the sides. It is a small scale with the female about 1/20-inch long. The male is about two-thirds the size of the female. The females vary in color from dark brown or gray to nearly black. Males are white. The female lays 10 to 16 eggs, which remain protected under her body until they hatch. In one to three weeks, bright yellow immature forms called crawlers hatch from the eggs. A typical symptom of tea scale infestation is yellow splotches on the upper surface of leaves. With a large infestation, the undersides of the leaves are covered by a cottony mass.
Adult tea scales (Fiorinia theae) on underside of camellia leaf.
Joey Williamson, ©2014 HGIC, Clemson Extension
Cottony camellia scale (Pulvinaria floccifera) is a soft scale that infests not only camellia, but also holly, hydrangea, English ivy, euonymus, maple, rhododendron, yew, and pittosporum. The adult scale is flat, 1/8-inch in diameter and yellowish-tan. As with other soft scales, cottony camellia scale produces large amounts of sugary honeydew, which both attracts ants and causes the leaves to become covered with black sooty mold.
The adult cottony camellia scale females lay ovisacs, which are the cottony white egg masses, during the early summer. The eggs hatch in summer, and the crawlers (small mobile immatures) will move around on foliage to find a place to feed on the lower leaf surfaces. Foliage with a heavy infestation may turn pale green or yellowish.
Prevention & Treatment: With a light infestation, scales can be scraped off the plant and discarded. If only a few leaves are infested, hand picking and destruction of infested leaves is very effective.
Cottony camellia scale (Pulvinaria floccifera) on lower leaf surface of sasanqua camellia. The adult scale is flat and yellowish-tan, and the ovisacs, which contain the eggs, are elongate and white.
Joey Williamson, ©2014 HGIC, Clemson Extension
The best time to spray with refined horticultural oil is in late winter or early spring, and the danger of cold weather has passed. This will kill many adults, crawlers, and eggs by smothering them.
Apply horticultural oil sprays at a 2% solution (5 tablespoons oil per gallon of water). Spray the plants thoroughly, so that the oil spray drips or “runs off” from the upper and under sides of leaves, twigs, and plant stems. Spray when temperatures will be above 45 °F for the next 48 hours. Spray when no rain is in the forecast for 24 hours.
Spraying an insecticidal soap later during the growing season will help control crawlers, as well as adults. Spray two applications, 10 days apart. Spray when the temperature is between 45 and 90 degrees, and spray in the evening to slow soap drying time and to increase effectiveness. See Table 1 for examples of brands of horticultural oils and insecticidal soaps.
Most contact insecticides are effective only against the crawlers. In addition, using a contact insecticide against scales can result in the deaths of naturally occurring enemies of scales (predators and parasites). As such, contact insecticides generally should be avoided if possible.
With tea scale, crawler activity coincides with the flush of new plant growth in the spring, but with cottony camellia scale, crawlers emerge in early summer. To determine when to best spray with a contact insecticide (or an insecticidal soap), monitor the crawler emergence with sticky cards, tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the South Carolina coast.
Insecticides labeled for homeowner use against scale crawlers (only) include acephate, malathion, cyfluthrin, bifenthrin, cyhalothrin, and permethrin. Of these insecticides, acephate may give the best control, as it is a foliar systemic insecticide. See Table 1 for examples of products. As with all pesticides, read and follow all label instructions and precautions.
A soil application can be used once in the spring around the base of the infested plant with a product containing dinotefuran to control both soft and armored scales. See Table 1 for examples of products, which may be found at landscaper supply stores. Read and follow all label instructions and precautions. Soil applications may be used in addition to sprays with horticultural oil or insecticidal soap. Note: Soil applied products containing imidacloprid do not effectively control armored scales, such as tea scale, or soft scales, such as cottony camellia scale. On evergreen shrubs like camellias, dinotefuran may be applied either in the early spring or early fall.
Bud Drop: Camellia flower buds may drop from the plant before opening, or the tips of the young buds may turn brown.
Prevention & Treatment: Bud drop can be caused by several different factors. One of the most common causes is large fluctuations in temperature or moisture. Camellias perform best planted in areas with uniform moisture that are not too wet or too dry. Freezing temperatures can cause buds to drop before opening. Hot weather during the fall or spring may encourage shoot growth and cause the plant to drop its flower buds. Avoid planting varieties that bloom late in the spring and plant in a shadier, cooler location to help prevent this problem. Other plant stresses from a lack of nutrients or poor drainage can cause flower buds to drop. Camellia bud mites cause buds to develop slowly and either open late or fall off before opening. Camellias that drop their buds year after year may have a varietal problem, or it may a problem, of location that can be solved by transplanting.
Sunscald: Camellias planted in full sun or against a south- or west-facing wall often get sunscald. Leaves will develop scorched or bronzed areas on the side of the plant directly exposed to the sun. Leaf-spotting fungi may infect the damaged leaves. Sunscald is a particular problem on camellias transplanted from shaded to sunny locations.
Prevention & Treatment: Prevent sunscald by planting in a shadier location or providing more shade to their present location. Once the leaves have turned brown, they will not recover.
Oedema: Oedema (sometimes spelled edema) 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 oedema will occur primarily on the lower leaf surfaces, and at first appear as small, water-soaked, greenish-white raised areas.
Advanced stages of oedema on lower leaf surface of camellia.
Photo by Dr. Jean Williams-Woodward, Extension Plant Pathology, University of Georgia
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. Oedema 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.
Prevention & Treatment: 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.
Note: Control of diseases and insects on large shrubs and trees is usually not feasible, since adequate coverage of the foliage with a pesticide cannot be achieved.
Table 1. Fungicides & Insecticides to Control Camellia Diseases & Insect Pests.
|Active Ingredient||Examples of Products|
|Acephate||Bonide Systemic Insect Control Concentrate|
|Bifenthrin||Ortho Bug-B-Gon Insect Killer for Lawns & Gardens Conc.; & RTS1
Ferti-lome Broad Spectrum Insecticide Concentrate
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate
Monterey Turf & Ornamental Insect Spray
Bifen I/T Concentrate
Talstar P Concentrate
Up-Star Gold Insecticide Concentrate
|Captan||Southern Ag Captan Fungicide WP
Bonide Captan 50% WP
Drexel Captan 50W
Arysta Captan 50% WP
Hi-Yield Captan 50W Fungicide
|Copper Fungicide||Bonide Liquid Copper Concentrate (1.8%)
Camelot Fungicide/ Bactericide Concentrate (1.8%)
Natural Guard Copper Soap Liquid Fungicide Concentrate (1.8%)
Bonide Copper Fungicide Spray or Dust (7%)
Monterey Liqui-cop Fungicide Conc. (8%)
Southern Ag Liquid Copper Fungicide (8%)
|Cyfluthrin||Bayer BioAdvanced Vegetable & Garden Insect Spray Concentrate; & RTS1|
|Dinotefuran||Ortho Tree & Shrub Insect Control Ready to Use Granules (2%)
Valent Brand Safari 2G Insecticide (2% granules)
Gordon’s Zylam Liquid Systemic Insecticide (10%; drench2)
Gordon’s Zylam 20SG Systemic Turf Insecticide (20%; drench)
Valent Safari 20SG Insecticide (20%; drench)
|Horticultural oil3||Ferti-lome Horticultural Oil Spray Concentrate
Bonide All Seasons Spray Oil Concentrate
Southern Ag ParaFine Horticultural Oil Concentrate
Espoma Earth-tone Horticultural Oil Concentrate; & RTS1
Monterey Horticultural Oil Concentrate
Summit Year Round Spray Oil Concentrate
|Lambda or Gamma Cyhalothrin||Spectracide Triazicide Insect Killer for Lawns & Landscapes Conc.; & RTS1
Martin’s Cyonara Lawn & Garden Concentrate
|Malathion||Spectracide Malathion Insect Spray Concentrate
Southern Ag Malathion 50% EC
Hi-Yield 55% Malathion Insect Spray Concentrate
Tiger Brand 50% Malathion Concentrate
Gordon’s Malathion 50% Spray Concentrate
Bonide Malathion Insect Control 50% Concentrate
Martin’s Malathion 50% Concentrate
Ortho Max Malathion Insect Spray Concentrate
|Mancozeb||Bonide Mancozeb Flowable with Zinc Concentrate
Southern Ag Dithane M-45
|Permethrin||Bonide Eight Insect Control Vegetable, Fruit & Flower Concentrate
Bonide Total Pest Control Outdoor Concentrate
Hi-Yield Indoor/Outdoor Broad Use Insecticide Concentrate
Bonide Eight Yard & Garden RTS1
Tiger Brand Super 10 Concentrate
|Thiophanate Methyl||Cleary’s 3336-WP Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
Note: Pollinating insects, such as honey bees and bumblebees, can be adversely affected by the use of pesticides. Avoid the use of spray pesticides (both insecticides and fungicides), as well as soil-applied, systemic insecticides unless absolutely necessary. If spraying is required, always spray late in the evening to reduce the direct impact on pollinating insects. Always employ cultural controls first, then use less toxic alternative sprays for the control of insect pests and diseases. For example, sprays with insecticidal soap, horticultural oil, neem oil extract, spinosad, Bacillus thuringiensis (B.t.), or botanical oils can help control many small insect pests and mites that affect garden and landscape plants. Neem oil extract or botanical oil sprays may also reduce plant damage by repelling many insect pests. If soil applied insecticides are used, make applications immediately after flowering to reduce the amount of insecticide exposure to pollinating insects. For more information, contact the Clemson Home & Garden Information Center.
Common Pests and Diseases of Camellias
There are not many – but you will encounter a few pests and diseases with camellias. Prevention is worth an ounce of cure in most cases.
Scale & Mites
Scale insects and Mites are both insects that can attack your camellias. Both usually start at the underside of the leaves.
Scale is noticed by its white powdery substance under the leaves and results in a yellow mottled appearance to the upper leaves. If left untreated- it can spread to all parts of the plant and nearby plants as well.
Mites are actually spider-mites. They live and reproduce on the underside of the leaves are visible by their faint dust like appearance. Their damage causes a bronzing look to the upper side of the leaves.
Both of these insects can be controlled with regular treatments with oil spray or insecticides.
Aphids are small green ant-like insects that are usually visible in the spring when the new growth appears. You can treat with insecticides to control aphids which can damage the foliage on your camellias. Aphids also attract ants that feed on their secretions.
The most common symptom of aphids is the black sooty mould which can be found covering the top of leaves. The only cure for this is to treat with insecticide and then wipe the mould from each leaf. Its a tedious job, but well worthwhile. Treat again with insecticide in early Spring to avoid a repeat infestation.
Petal blight is a disease of the blooms that usually appear in February or March of each year. It is characterized by brown splotches that can leave blooms with an undesirable appearance. There is no cure for petal blight and picking up blooms will only minimize the problem as spores can travel by the billions up to 5 miles away! Planting early blooming varieties can give you some relief from Petal Blight.
Dieback is a common disease and affects some camellias more than others. It is spread by splashing water, wind or unclean pruning shears. The spores enter through wounds on the plant and can cause limbs to “die” . If infected in the lower part of the plant, entire plant death could occur. It can be prevented by sanitation, disinfecting pruning shears, and possibly the use of a fungicide if you think you have problems with dieback to prevent it from spreading to other plants.
Canker and Dieback (fungus – Glomerella cingulata): Sudden wilting of branches is usually the first indication of disease. Gray blotches appear on bark of stem or branches. Underlying wood dies and bark may split to form open wounds or cankers. Pinkish pustules or spore masses may be seen in these cankers during moist periods. Leaves on affected branches turn chlorotic and branch tips die back. Plant in well-drained soil that has the proper pH and fertility level. Avoid excessive nitrogen fertilization. When dieback occurs, prune out and destroy diseased twigs. Prune several inches below visible canker, and use a commercial wound dressing on all cuts. Spraying plants during wet periods and during the period of normal leaf drop with a fungicide will help control the disease.
Petal Blight (fungus – Sclerotinia camelliae): Petal blight affects only the flower portion of the plant. The first evidence of infection is the appearance of small, brown, irregular-shaped spots on the petals. Affected petals have a “veined” appearance and the tissue remains firm. Entire flower turns brown in 24-48 hours and usually drops. The disease generally occurs during the spring. Remove and destroy all infected plant tissue. Apply fungicide to the soil just prior to bloom to prevent germination of overwintering spores. Thoroughly cover all areas under the plant and at least a 10 foot radius around each plant. Applications of a foliar fungicide at the first sign of disease and at 7-14 day intervals is effective.
Leaf Gall (fungus – Exobasidium camelliae): Young leaves and buds may be infected. Leaves become thickened and succulent and may be larger than normal. The color changes from light green to nearly white. Little damage occurs but the plant appears abnormal or diseased. Pick young galls and destroy. Spray with fungicide before leaves open.
Leaf Spots (fungi – Phyllosticta camelliae, Pestalotia guepini and algae –Cephaleuros virescens): Various sized spots on the leaves. Small, black pinpoint dots may be in the dead leaf areas. Control requires preventive fungicidal sprays at two week intervals. Include a spreader sticker to increase effectiveness of sprays.
Ring Spots (virus): Occurs mostly in East Texas. Light green or yellowish rings surround islands of green in the leaves. Destroy diseased plants. Propagate from disease-free plants.
Yellow Mottle Leaf (virus): Irregular, yellow patterns on some leaves. No cure available. Propagate from disease-free plants.
Bud Drop (physiological): May occur as a result of overwatering, inadequate moisture in the soil, insufficient light, excessively high temperatures, severe freezing during the winter or a pot-bound condition of the roots. Also, certain camellia varieties shed their unopened bloom buds as a result of insufficient cold during the winter. Fertilize and water properly. Keep plants healthy by controlling diseases and insects.
Oedema or Scab (physiological): Corky bumps or raised areas on leaves. Usually due to excessive water in soil.
Sunburn (physiological): Leaves have brown or faded green areas. Occurs on side of bush directly hit by the sun. Particularly a problem on bushes transplanted from a shaded to a sunny location.
(physiological): Margins of leaves turn light brown and dry. Camellias cannot tolerate high soil salinity.
How to Manage Pests
Camellia petal blight—Ciborinia camelliae
Camellia petal blight, also called Ciborinia petal blight, affects all cultivars of Camellia japonica. Camellia sasanqua is infected less often in California.
Infection by the Ciborinia camelliae fungus initially causes small, brown, irregularly shaped blotches in petals. Spots enlarge rapidly until the entire flower is brown and dead. Except when wet, blighted petals are dry or leathery but do not crumble when handled. Blossoms drop prematurely to the ground, often as intact flowers. Prominent dark brown veins give infected petals a netted appearance.
Damage resembling that of camellia petal blight is also caused by Botrytis blight, frost, old age (overmature blossoms), and injury due to chemicals, rough handling, or wind. Symptoms that distinguish camellia petal blight from these other causes include petal veins darker than the surrounding tissue, infections beginning near the central part of the flower (not appearing first near petal margins), and symptoms that occur only on petals.
Ciborinia camelliae produces dark, hard, irregular-shaped sclerotia at the base of infected flowers, where they replace the calyx lobe. Depending on the extent to which nearby sclerotia unite, they typically range in size from 1/12 to 1 inch. Sclerotia can lie dormant for several years on or near the soil surface.
During winter and spring when camellias blossom, sclerotia produce light brown saucer-shaped apothecia (inverted mushroomlike bodies) about 1/5 to 3/4 inch in diameter. Apothecia forcibly discharge large numbers of spores that are carried by wind onto emerging blooms, where they germinate and infect flowers when they are wet.
Pathogen development is favored by wet or humid conditions and mild temperatures (about 59° to 70°F) during bloom. Outbreaks are initiated by sclerotia-infested soil received with new plants and by sclerotia persisting beneath established plants that have previously been infected. Sclerotia continue to produce apothecia for 3 to 5 years after being introduced into soil and the pathogen cannot be eradicated once present.
Prevention is the best control. Remove the top layer of potting soil when new plants are purchased and replace it with pathogen-free soil. Plant camellias in a well-ventilated location and avoid overhead irrigation. Pull off infected flowers as they appear and collect fallen blossoms and dispose of them in a covered location away from camellias.
Do not add camellia petals or leaves to mulch that will be used around camellia, even if it has been composted. It is difficult to expose camellia debris to the 140°F required to kill all of the Ciborinia propagules by composting.
Each year, when blossoms are no longer present, apply a fresh layer of pathogen-free organic mulch and maintain a 4-inch layer of organic mulch beneath and somewhat beyond plants to suppress pathogen spore production. Remove fallen petals and other camellia debris before applying fresh mulch, but otherwise avoid moving or disturbing existing mulch where fungi may be present. Keep mulch thin near the trunk or several inches away from the trunk.
Spraying an appropriate fungicide during bloom can help to reduce infections. Depending on the fungicide, reapplication may be needed every 10 to 14 days while conditions remain suitable for the pathogen. Use fungicides only in conjunction with recommended sanitation and cultural practices.