PESTS AND PESTICIDES

Cereal crop pests

The UK climate is ideally suited to producing high yields of cereal crops such as wheat. However, our climate also favours the growth of diseases and pests, which reduce yield and increase the cost of production for farmers. In natural ecosystems, plant pests and pest predators reach a balance. However, large areas of a single plant species such as wheat provide the ideal conditions for pests to breed. Insect pests of the wheat crop include slugs, aphids and midges.

Pest management can involve cultural and chemical control.

• Cultural control involves the use of crop rotation, careful choice of plant variety, management of sowing date and seed rates. This control will encourage pest predators and help to reduce the use of chemical controls.
• Chemical control means the application of pesticides. Insecticides can be used to kill them but must be chosen with care to ensure they do not harm natural species.

There are three main types of pesticide that are used to protect wheat crops in the UK:

• insecticides: to control insect pests
• fungicide to control disease caused by fungi
• herbicides: to control weeds.

Pesticides are extremely expensive and because of the safety risks associated with them, there are a number of regulations governing their use and storage. For example, spraying can only take place when the conditions are correct and the crop is at the right stage of growth. Ideally there should be a light breeze without rain.

From 1992–2002, pesticides were used increasingly often on arable crops including wheat. But the amount used actually fell – new products needed lower doses to be active, and research showed that reduced applications of pesticides were effective. At the same time, there was a big drop in the use of older, more environmentally-damaging pesticides. Today's farmers must balance using pesticides for a good crop yield with protecting the environment.

Grain store pests

Insects

Insect pests in the grain store include:

• storage mites: extremely small but they are widely distributed and breed very rapidly; they can survive unfavourable conditions by going into a 'resting stage'. Mites damage grain directly by eating the germ or hollowing out the seeds. They can also carry fungal spores and bacteria such as salmonella. Very accurate application of chemical methods can be used to control mites.
• primary storage insects (beetles and moths): invade grain from previous harvest residues, are specialised for the grain storage environment and breed at low moisture content and relatively low temperature. A few species, e.g. the grain weevil, develop inside the grain. Resistance to pesticides makes some insects, e.g. the saw-toothed grain beetle, hard to control.
• secondary storage insects (e.g. fungus feeders, spider beetles and booklice): may invade grain from nearby sources, such as haystacks. They only damage poorly conditioned or already infested grain. Occurrence is seasonal and populations build up slowly.

Prevention by cooling and drying the grain is preferable to chemical control. However, if monitoring shows infestation is present or levels are rising, pesticide use may be justified.

Fungi

In the right conditions, mostly through incomplete or slow drying of the grain, fungi (or moulds) develop rapidly in the store. They cause discolouration and off-odours. They may produce mycotoxins, which are toxic to humans and animals. Visibly mouldy grain will be already tainted and mycotoxin production may have started. However some species of mites feed on fungi and may mask evidence of fungal growth. Farmers and millers should not sniff mouldy grain as spores can cause 'farmer's lung', an allergic disease which affects the respiratory system. Controlling the moisture and temperature of the grain helps to reduce fungi development.

Rodents

Rats and mice can cause problems in the grain store including:

• diseases which affect humans, e.g. Weil's disease, salmonellosis, cryptosporidiosis, toxoplasmosis and listeria.
• damage by eating grain or by gnawing, to buildings and fittings (e.g. wiring) as well as machinery
• grain contamination with faeces, urine, hair and carcasses.

The control of most rat and mouse infestations should be achieved in 3–4 weeks, but it is better to make the environment unfriendly to rodents. Courses of action include removing food and edible material, eliminating free water sources, proofing the store against rodents, and applying rodenticides safely where rodent activity is detected.

Birds

Birds can cause the following problems:

• disease transmission, e.g. salmonellosis, ornithosis and Newcastle disease
• eating grain
• grain contamination with faeces, feathers, carcasses and nest material
• introduction of primary and secondary stored product insects, and subsequent contamination of stores.

The risk can be reduced by cutting down access to food and shelter for birds, blocking entry points and using netting or 'birdwire' to prevent roosting.

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