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 (isolated from other plants) for at least a month before adding new acquisitions to an existing collection.
Check susceptible plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the damage to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
- Dead leaves and pruning’s should be removed from the greenhouse as these may have mealybugs or eggs on them
- It can be simpler to dispose of heavily affected plants rather than try to eliminate mealybugs
- Plant can tolerate some levels of mealybug, although populations can quickly build if left unchecked
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., Leptomastidea spp.
spp.) are also sometimes available for use against these insects. The parasitic wasps can give control of mealybug populations where population levels are fairly low.
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 pesticide control. They are available by mail order from suppliers of biological controls
Due partly to the waxy covering mealybugs are difficult to control with insecticides, affected plants should be sprayed thoroughly. In many cases it may be impossible to eliminate mealybugs.
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear for Fruit and Veg) can give some control of glasshouse mealybugs. These pesticides have a very short persistence and so may require reapplication to keep mealybug numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults.
- Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against aphids (e.g. Ecofective Bug Control, RHS Bug and Mildew Control, SB Plant Invigorator and Westland Resolva Natural Power Bug & Mildew). These are not considered organic.
- More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. On edible plants make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval. Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Pesticides for gardeners (pdf document)
Biological control suppliers (pdf document)