PESTS AND PESTICIDES
Cereal crop pests
The UK climate is ideally suited to producing high yields of cereal crops
such as wheat. 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 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
used. This control will encourage pest predators and can 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 are only sprayed for good reason.
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 the
pesticides they need to give 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. Chemical methods can be used to control mites
but very accurate application is required.
- 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 using cooling and drying of 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:
- carrying diseases which affect humans, e.g. Weil's disease,
salmonellosis, cryptosporidiosis, toxoplasmosis and listeria.
- direct damage by eating grain
- grain contamination with faeces, urine, hair and carcasses
- damage, by gnawing, to buildings and fittings (e.g. wiring) as well as
machinery.
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 problems in the grain store including:
- disease transmission, e.g. salmonellosis, ornithosis and Newcastle
disease
- direct damage by 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.
