Tuesday, 29 March 2016

Organic Approach to Pest Control Part VI - Citrus

Green lacewing - a beneficial bug


A few guidelines for good citrus health with some organic remedies:

Practice good hygiene by never leaving fruit to rot on the ground.

Keep an eye out for Bronze Orange Bugs - they often give away their presence by their foul smell. The young pale green nymphs appear in winter, their colour changing through orange to bronze as they grow into adults. They can be serious pests - causing flower and fruit drop by sucking on the stalks. Hand removal is possible (although it is recommended to wear eye protection, long sleeves and gloves) by placing them into a bucket of hot water with some dish washing liquid.



The adult spined citrus bug has projecting horns on either side of its head, the young change colour from yellow through orange and finally to green. They attack the fruit, causing shedding of the young fruit and dry patches in mature fruit - control by hand picking as above.



Collar Rot is a soil fungus that attacks the tree trunk at ground level and if left untreated it can kill the tree. The first signs of Collar Rot are splitting, oozing bark and yellowing foliage. Cutting the bark back with a sharp knife or chisel until undamaged bark is reached is the main treatment. Avoid wetting the trunk when watering and keep mulch away from the trunk. Make sure that there is good air circulation and excellent soil drainage.



Citrus Gall Wasp is something we all need to keep an eye out for. Prune out any affected twigs and branches before August and either burn or double bag and place in Council red bin. If there are any tiny holes in the gall - that's it folks, they have already hatched!!




Scab is a fungal disease that affects young fruit (especially lemons) causing raised light brown corky scabs on the surface of the fruit. Good hygiene and improving air circulation will help this problem.



Citrus Leaf Miner causes ugly distorted leaves with silvery trails in the leaf tissue, especially in spring and summer. Eco Oil is a non-toxic control, spray when new growth is about 1cm long and reapply every 2-3 weeks.

Scale are sap-sucking insects with small, round shells and are often found along the veins of leaves and the stems of plants. They look like small bumps and can be mistaken for part of the plant, as adults do not move. Eggs are laid under the scale or white louse scale can seriously damage or kill young citrus trees. To control treat with Lime Sulphur spray in winter. Other scale outbreaks can be controlled with Eco Oil, which works by smothering the scale. Some soft scales, including white wax scale and black scale, secrete large amounts of 'honeydew' which causes problems by sticking to the lower leaves where it is fed on by a fungus called Black sooty mould. Honeydew also attracts ants, which feed on it. The ants can 'farm' the scale, protect them from predators, so the first step is always control any ants, as without their protection the abundance of natural enemies in an organic garden will usually be able to keep scales under control. Keep ants out of your trees by banding the trunks with horticultural glue. Prune any low branches that are touching the ground and make sure that tall stems of grass aren't providing a 'ladder' for the ants. You can read more on scale here.


Improving the environment for the natural predators of scale is a long-term strategy that will eventually pay off. Natural enemies of scale include lady beetles, lacewings, spiders and tiny parasitoid wasps. Many beneficial insects that feed on garden pests need nectar and pollen for food during part of their life cycle. Growing a year-round supply of suitable flowers such as Green Harvest's 'Good Bug Mix' which will maintain beneficial insect populations throughout the year. This mix contains colourful re-seeding annual and perennial flowers including red clover, alyssum, cosmos, marigolds, Queen Anne's Lace, buckwheat, lucerne, dill caraway, coriander and phacelia and gypsophila. There will be blooms for much of the year, providing nectar, pollen and habitat for wild and introduced beneficial insects, such as predatory mites and tiny micro wasps. ladybirds, lacewings, hoverflies, tachnid flies and predatory beetles. These insects or 'good bugs' are generally small with correspondingly small mouthparts, so they are only able to feed on particular flowers with suitable attributes. By providing a plentiful food supply these 'good bugs' can live longer and reproduce more. Small insect-eating birds are also helpful in controlling scale; attract them by providing safe nest sites and a constant supply of water.






Black sooty mould is a fungus that feeds on honeydew. Honeydew is produced by a range of insects including aphid, scale, mealybug and planthopper. Sooty moulds make a plant look really unattractive and interferes with photosynthesis. To get rid of the sooty mould you need to address the pest problem. Once you have that under control and they are no longer producing the honeydew, the sooty mould will dry up and flake off.






Spider mite there are some easy things you can do that will have a big impact on spider mite numbers. Try a high pressure hosing in the early morning, three days in a row. An unlikely pest control device is a hand held vacuum cleaner - after vacuuming, tip the contents immediately into a plastic bag and freeze for a couple of hours. You can control whiteflies doing this as well. Pruning back affected plants and removing infested leaves will reduce pest numbers. 

Mealybug treat with Eco-oil, horticultural glues, natrasoap or pyrethrum. But first address the issue of the ants - one comes with the other usually.



Aphids are sucking insects that have a large number of natural enemies including some of the beneficial insects mentioned above. They tend to be a problem where the use of pesticides is wiping out the natural enemies or at times of the year when natural enemies are not present in large numbers.

Whitefly are small white moth-like flies. Eggs are laid on the undersides of leaves and hatch in about 8 days. Both newly hatched 'crawlers' and adults feed by sucking the sap from the underside of the leaf. They also excrete 'honeydew' which causes problems with black sooty mould. Vacuming in the early morning and freezing for some hours seems to be quite effective. Companion planting with nasturtiums can often help.


Snails - start with a garden clean up to reduce snails and slug breeding sites. Remove any old wooden boards and other garden rubbish. Check any pot rims and around drains and retaining walls. Have a bucket of soapy water at the ready and drop them in as you find them. Handpicking, will over time, greatly reduce the number of snails - it is less effective for slugs. A really good way is to give financial reward to children and make it a fun activity by torchlight to collect as many snails as possible. Of course, if you have ducks snails will most probably not be a problem for you!




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