by Andrew Raper
Camellias’ reputation for being hardy and sustainable garden shrubs is well deserved. However from time to time some seasonal condition or insect event may cause concern in the home garden. Before reaching for the most lethal or toxic chemical to eliminate the problem, consider which solution will have the smallest impact on you and your beneficial friends in the garden. Most insecticides cause a blanket kill effect (non selective) on all the insects, spiders and mites wiping out both good and target bugs. This is now known as a vacuum effect that is unfortunately recolonised by the bad bugs first. Camellias Victoria recommends ‘integrated pest management’ practices be employed rather than a “ground zero” approach to pest control, i.e. tolerate minor infestations for the sake of friendly predators such as lady birds, praying mantis, native birds, etc.
These small and easily recognised insects are usually associated with new growth. They can be green, black or brown in colour and may occur on flower buds during autumn and even winter and new growth in spring. Aphids are sucking insects whose damage weakens the host camellia and are often associated with the spread of more serious diseases. Squashing them between your fingers can attain control of small infestations. Some people recommend squirting with a strong spray of water, be cautious, this may only be spreading the problem further around the garden. For chemical control, you should ask for a modern low toxic and, most important, selective insecticide eg. ‘Confidor’.
Two types are found in quantities which may require more than an occasional walk past squeezing the rolled up growth tips. They are the cabbage white and the light brown apple moth larvae. For a major outbreak requiring spraying, use a chewing insect spray, eg ‘Carbryl’. A biological spray ‘Dipel’ may be applied, this has proven effective in orchards and vineyards. Whilst it is not 100% effective once the microbes are active a high level of caterpillar control is achieved.
May be found on camellias where plant vigour is not strong, also large containers, heavy shade and over dry conditions seem to promote scale. Scales are small roundish insects that may be found on the underside of the foliage or on the stems. They can be white, brown or black and are often found in conjunction with ants. The ants offer protection to the scales and also aphids in exchange for excess sap that they exude that the ants use for food. Control of the scale will also make the ants move on. Use “Pest Oil” or “Malascale” as recommended and use a follow up spray to kill off any secondary hatchings.
European garden weevil damage is easily identified by tell-tale scalloped chew marks around the outside of the leaf. The damage is unsightly but usually localised to a small area of thegarden. Weevils are nocturnal so identification can be tricky as catching one isn’t easy. The traditional method is by far the easiest using trap boards. Weevils only move under cover of darkness so a plank (50cm x 15cm) strategically placed near the affected plant flat on the ground gives this villain a hiding spot. You will find your weevil waiting for you in the morning. Chemical control would be a residual chewing insecticide, eg. “Carbryl”.
Two-spotted mite (also known as red spider mite) may choose camellias as a host over the hotter months. This seems more common in garden situations where dry, still conditions are constant particularly along fences and in shade houses where over-crowding occurs. Chemical control of mite has become nearly useless due to chemical resistance of the mite. Changing the host environment is beneficial, more direct watering of the foliage, pruning overhead branches to reduce shading is also effective.
They are so small and difficult to see without some magnifying device that they often go undetected. They are wormlike and range in length from 0.1 to 0.3 mm. They also have considerable reduction in body structure; the two pairs of hind legs and most body setae have been lost and the front legs are reduced. The symptoms they produce include odd colour patches on leaf surfaces, leaf margins that roll inward or downward, swollen and distorted leaves, galls, russetting, and “witches brooms”. The symptoms are often confused with the symptoms of growth regulator or herbicide damage.
Biological Control: Predatory mites are voracious eaters will devour the imbalance and then establish their own balance in your garden. Note: predatory mite are very susceptible to many chemical sprays, use with caution. Predatory mites can be bought by mail order and sourcing through the internet is a good way to access them.
This unsightly black sticky substance is actually growing on the residue products secreted by aphids and scale. Identification and elimination of the pest as previously discussed will correct this situation, followed by an application of white oil or pest oil to eliminate the sooty mould spores.
Botrytis (Grey Mould)
This is one of the most common airborne fungal diseases affecting camellias. It causes premature aging of blooms and brown spots especially in the centre of flowers. To confirm the presence of botrytis turn the affected flower over and look for grey hairlike growths around the base of the flower. Botrytis may also result in pink circles on the front of the flower as in roses. Botrytis is a seasonal event commencing around late April with sasanqua flowering and continuing throughout the entire season. Cool, moist and very still conditions favour botrytis and, infrequently, these are constant enough to make this disease a big problem for home gardeners. Keeping potted plants spaced and maintaining affected bushes trimmed to allow better air circulation make it unlikely problems will occur. If chemical control is required most rose fungicides such as Triforine or Mancozeb contain agents to combat Botrytis.
Camellia Dieback and Canker: (Glomerella cingulata.)
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 and 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. There are fungicides available to treat the affected areas which 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.
Leaf Gall: (Exobasidium camelliae)
This disease is more common on sasanqua varieties of camellia (Camellia sasanqua) than on Camellia 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. The galls later 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 and 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.
Phytopthora and Pythium
Young cuttings and seedlings are especially prone to these root rot diseases particularly when in potting mixes rather than the garden. The use of “Fongarid” as a protective drench is a worthwhile practice for all propagators to make routine, even if only a few cuttings are attempted a year. Propagation trays or pots should be washed down in household bleach at recommended rates for floor cleaning.
In larger plants root rots are more likely to occur as secondary issues taking hold only if there are pH issues or micro nutrient problems. Regular re-potting even if no increase in size is required (say every second year), fertilizing regularly especially in pots in spring and autumn with a complete fertilizer, and maintaining a soil pH at a range of 5.5—6.5 will keep healthy camellias.
Camellia Petal Blight
Just the mention of this disease leaves Australian camellia growers in a cold sweat! At present camellia petal blight is not in Australia, however our friends in New Zealand and the UK are the most recent additions to the list of infected countries, which includes China, Japan, USA and most of Western Europe. This fungus disease uses air currents to spread, its spore landing on camellia blooms, turning them brown and to mush in as little as a day. The devastated bloom falls to the ground where the full cycle of the fungus is completed and ready for repetition next season.
Chemical control has to date been almost useless as chemicals are only in the developmental stage or very expensive. Even cleaning up the spent blooms will only help a little as wind spread has been found to be a massive 300 kilometres a season. The greatest risk to Australia is an illegal imported plant being brought in outside our stringent quarantine services. Soil contaminated shoes are also a major threat so declare your shoes to the Quarantine officer at the airport for inspection. They are happy to assist you with this.
Camellia flower buds may drop off of the plant before opening or the tips of the young buds turn brown.
Prevention and 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 autumn 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 due to a lack of nutrients, poor soils or drainage can cause flower buds to drop. Excessive use of nitrogeneous fertilisers such as, Blood & Bone and Nitrosol can also push new foliage growth at the expense of flowers. These fertilisers are best applied just after the flowering cycle to maximise the regrowth spurt. 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 a problem of location that can be solved by transplanting.
Camellias planted in full sun or against a north or westfacing wall often get sunscald. Leaves will develop scorched or bronzed/yellow 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 and 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. Investigation of the sun hardiness of individual camellia classes and cultivars should also be investigated. By way of example and generally speaking, Sasanquas, Reticulatas, Hybrids and many darker flower coloured Japonicas can endure more exposure. This is also predicated upon the presumption that, they live in good soil, receive adequate water and are mulched during warmer months.
Frost is more likely to damage the flowers resulting in browning off and shrivelling. Although rainfall can also cause this affect, frost damage can be more pronouced. Lighter coloured cultivars are particularly suseptible to frost and weather damage and should be sited in a more easterly aspect and not facing towards prevailing, wet or frosty weather directions.
Drought: Severe drought conditions and all the stresses related to them such as, inadequate watering, heat stress can result in the underperformance of your camellias. This can equate to some levels of defoliation and poor flower-set or qualtity. However, established camellias have proved themselves to be extremely drought tolerant.
This disorder appears as numerous small bumps on the lower side of leaves or on stems. The “bumps” are tiny clusters of cells that divide, expand and break out of the normal leaf surface. At first, they form tiny greenish-white swellings or galls. Later, the exposed surface of the swellings becomes rustcolored with a corky texture. Oedema is a condition promoted by abundant soil water taken up by the plant in warm weather. Under these conditions roots absorb water faster than it is lost through the leaves, especially when a sudden cool weather change occurs. This excess water accumulates in the leaves and then is expelled by bursting leaf cells.
Prevention and Treatment: This problem is not caused by disease or insects. Oedema can be caused by overwatering, especially during cloudy, humid weather. Water less frequently and avoid overcrowding plants to increase air movement.
It is advised that correct protective clothing be worn while engaged in remedial spraying, e.g. full body covering clothing, gloves, glasses and face mask. As a further suggestion, if children or pets are an issue, make this the last job of the day so that they are retiring from the garden as you are applying sprays. Never exceed the manufacturer’s recommended application mix rates. Do not apply sprays in climatic temperatures over 25°C. Remember that an environmentally friendly outcome is a safe and sustainable outcome.
Andrew Raper is the owner of Rhodoglen Wholesale Nursery, at The Patch, which is located in the picturesque Dandenong Ranges finging the north of Melbourne. This nursery is at the cutting edge of camellia and other plant material propagation.