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K20 Pest Control at KewProblems with pests
All plants can suffer from pests, and those growing at Kew are no exception. Aphids, spider mites, vine weevils and caterpillars can all damage or kill plants, by feeding on them or by transmitting diseases. Pest infestations can also look unsightly, for example black patches of sooty mould cover leaves where honeydew is secreted by aphids and whitefly larvae.
Many of the plants at Kew are particularly rare or valuable, so it is important that any pests do not cause excessive damage. From a global perspective, pest control is vital to ensure a continuing food supply to the world's population.
Problems with pesticides
Since the chemical revolution following World War II, synthetic pesticides have become the main response to pests in agriculture and horticulture. However, people are now realizing that while pesticides may be successful in the short term, they can cause many more problems than they solve. Using chemicals is becoming increasingly ineffective and inappropriate, for many reasons:
Most pesticides also kill the beneficial natural predators which would otherwise eat the pests and keep their populations under control.
As pesticides have been used for many years, many pests have become resistant to them. These "superbugs" can survive exposure to concentrations of pesticides which would normally kill them, usually by evolving ways to detoxify or avoid the chemicals.
Many pesticides cause environmental and human health problems.
Chemicals may not hit the pest. Pests may be living high out of reach, or hiding on the underside of leaves.
Some pesticides are poisonous to fish so cannot be used in glasshouses with ponds.
At Kew, glasshouses have to be closed when pesticides are used, to ensure the safety of visitors.
Kew uses Integrated Pest Management
Because of the problems associated with pesticide use, Kew now uses Integrated Pest Management (IPM) in all its glasshouses. The aim of IPM is to reduce the use of chemicals, employing instead a combination of pest control measures (biological, cultural and some chemical) that are less harmful to the environment and more effective.
Cultural control
Much of the work in pest control involves preventing pest outbreaks. Plant cultivation methods are very important. In many cases, controlling the temperature and humidity prevents pests from thriving. For example, spraying leaves with water reduces two spotted (red) spider mites and stops them spinning webs.
One of the most critical aspects of cultural control is to ensure that plants are maintained at peak health, as stressed plants can easily succumb to pests.
Chemical control
IPM can involve the use of small amounts of some carefully chosen chemicals. However, they are used only when absolutely necessary and applied so that they won't harm the beneficial insects.
Some chemicals only affect certain groups of insects, e.g. pirimicarb is sprayed to control aphids, and is less toxic to many other insects, such as ladybird larvae. Chemicals are applied at specific times appropriate to the insects' life cycles. Finally, application methods are designed to minimize the amount of chemical that is used. For example, spot treatment of affected plants is often used instead of blanket spraying the whole glasshouse.
Biological control of pests uses predators, parasites and pathogens:
Predators actively hunt out and eat pests. Lacewing larvae (Chrysoperla or Chrysopa species) eat aphids.
Parasites live on or in the pest, eventually killing it. Whiteflies (Trialeurodes vaporariorum) are parasitised by a small wasp, Encarsia formosa.
Pathogens, such as bacteria, fungi and viruses, cause disease to pests. A bacterium called Bacillus thuringensis infects and kills caterpillars.
These beneficial organisms can be encouraged by providing appropriate food and shelter, and not using chemicals that could harm them.
Using IPM - issues and benefits
IPM is far better for the environment than using pesticides alone. It is also more effective. Beneficial insects can usually reach places that direct spray can't - they will fly or follow pests into crevices. These biological control methods are, to some extent, self-regulating; as the pest populations grow, the predators respond. Also, using IPM avoids the problems of pest resistance which build up when large quantities of chemicals are used regularly. By using IPM in the glasshouses at Kew, less staff time is taken up by spraying pesticides (an uncomfortable job, due to all the protective clothing that must be worn), and the glasshouses are now rarely closed to the public for chemical application.
IPM is a complex method that requires detailed information and observation. Monitoring pest populations is crucial, so that they can be detected before they do too much damage. Trained staff at Kew regularly monitor plant health and populations of the pests and beneficial organisms. Sticky traps (pieces of cardboard or plastic coated with a tacky resin) attract and trap insects, so that staff can easily see which species are present.
To use biological control effectively, a detailed understanding of the biology of the beneficial and pest organisms is needed. Knowing the conditions that encourage the beneficials while discouraging the pests will help to balance the odds in favour of the "good guys".
Kew's research into pest control
Many well-known insecticides already come from plants. Pyrethrum and derris are examples. As plants have evolved to avoid being eaten, many contain compounds which are distasteful or toxic to insects. Scientists at Kew and elsewhere are using their knowledge about plants' natural defences to identify and develop new pesticides, for example azadirachtin from the neem tree (Azadirachta indica) and naphthaquinones from a slipper flower (Calceolaria andina).
Further information
Many biological control agents suitable for use in the home or greenhouse are available from garden centres or by mail order. Monthly gardening magazines are a good source of further information and addresses.
| Biological control of whitefly at Kew | ||||||
| Control agent | What is it? | How does it work? | Special requirements or conditions | |||
| Verticillium lecanii | Fungus | Infects and kills whitefly adults and larvae | Needs high humidity | |||
| Encarsia formosa | Parasitic wasp | Lays its eggs on whitefly larvae. The young wasp feeds on the pest eventually killing it. | Doesn't like high densities of whitefly larvae - the wasps get covered in sticky honeydew. | |||
| Macrolophus calliginosus | Predatory bug | Feeds on the larvae. It will also eat many other pests on Solanum plants, so some of these need to be | Thrives with high densities of whitefly. Lays its eggs on Solanum plants, so some of these need to be planted in the glasshouse. Will also feed on plant sap. Adults can fly, so have to be released into the glasshouses when the vents are closed, or they escape. | |||
