Citrus tree problems

~ mine is still outside but will be going into the greenhouse~ see the RHS report below re mealy bug

Mealybug
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last updated Feb 17, 2009

Phormium mealybug
Mealybugs. Image: RHS, Horticultural Science

Mealybugs are common sap-feeding pests that infest a wide range of houseplants and greenhouse plants. Mealybugs weaken plants and excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.
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* What is mealybug?
* Symptoms
* Control
* Biology

What is mealybug?

Mealybugs are common sap-sucking insect pests which tend to live together in clusters in protected parts of plants, such as leaf axils, leaf sheaths, between twining stems and under loose bark. They suck sap from plants, producing a sticky sugary substance, called honeydew, on leaves and stems.

Mealybugs are found mainly on greenhouse plants and houseplants, especially cacti and succulents, Bougainvillea, Saintpaulia, orchids (especially Phalaenopsis), Fuchsia, tomato, Hoya, Nerium oleander, Passiflora, peach, citrus plants and grape vines. Some other mealybug species can attack outdoor plants, such as Ceanothus, redcurrant, Laburnum and Phormium.

Most mealybugs thrive in warm conditions, which is why they are not usually a problem on outdoor plants. Mealybugs are active all year round on houseplants and in greenhouses.
Symptoms

You may see the following symptoms:

* Infestations are usually first noticed as a fluffy white wax produced in the leaf axils or other sheltered places on the plant. The insects or their orange-pink eggs can be found underneath this substance.
* Heavy infestations may result in an accumulation of honeydew. This makes plants sticky and encourages the growth of sooty moulds. Severe infestations will reduce plant vigour and stunt growth. Heavy infestations may cause premature leaf fall.
Control
Non chemical control

Female mealybugs do not fly or crawl far, so infestations are usually brought in on an infested plant. Inspect new plants carefully before putting them in a greenhouse or conservatory and, where possible, keep them in quarantine for a month or so before adding new acquisitions to an existing collection.

Dead leaves and prunings should be removed from the greenhouse as these may have mealybugs or eggs on them.

Biological control

A ladybird, Cryptolaemus montrouzieri, can be released into greenhouses to control mealybugs. Note that the ladybird's larvae look like large mealybugs! Both the adult ladybirds and their larvae are able to find and eat mealybugs and their eggs in confined spaces on the plants. Parasitic wasps (Leptomastix spp.) are also available for use against this pest.

The ladybird and parasitic wasps need relatively high temperatures and so are only likely to be successful during May to September. They are susceptible to most insecticides and should therefore be used as an alternative, rather than in addition to chemical control. They are available by mail order from suppliers of biological controls.
Chemical control

* A systemic insecticide, thiacloprid, is available as Provado Ultimate Bug Killer Ready-to-Use or Provado Ultimate Bug Killer Concentrate 2. This can be used on ornamental plants and greenhouse-grown tomatoes, peppers, cucumbers and aubergines, but not other edible plants.
* Other systemic insecticides that can be used against mealybugs are acetamiprid (Scotts Bug Clear Ultra concentrate or Bug Clear Ultra Gun) and thiamethoxam (Westland Bug Attack). These two pesticides are for use on ornamental plants only; thiamethoxam is restricted for use on container-grown plants.
* Growing Success Winter Wash (contains plant oils) can be used on peach and grape vines in December while they are fully dormant. Scrape loose bark off grape vines before treatment in order to expose hidden mealybugs. Spread newspaper under the vine to collect the bark scrapings for disposal.
* Other organic treatments include fatty acids (Bayer Organic Pest Control, Greenfingers Organic Pest Spray or Doff Greenfly and Blackfly Killer) or plant oils or extracts (Growing Success Fruit & Veg Bug Killer, Vitax Organic 2 in 1 Pest and Disease Control, Scotts Bug Clear for Fruit & Veg). These organic pesticides have a contact action and short persistence and so may require more frequent use. They can be used on edible plants.

if there are only a few then use meths/white spirit or acetone on a cotton bud to dab the critter. you can also squish them under finger and thumb. if you can bare too.

but the previous response is very thorough and spot on.

I had this problem again this year and have found a cure - I managed to find a company that supplies live bugs that eat the mealy bugs & eggs. They came in a glass tube and are very small about the size of a pinhead - about a dozen in all - the most difficult part was getting them out of the tube onto the tree - how ever it worked and in a week the lemon tree was clear and has been since - the odd thing is all the killer bugs that were introduced seem to have disapeared - don't know where to - but hey they did a good job!!