Biology Reference
In-Depth Information
(capable of killing various kinds of pest) but others are
more selective and some may be highly specific; modes
of action also vary. Choice of product will depend on
many different factors. Systemic materials (which are
absorbed through the leaves or taken up by the roots,
and then translocated through the plant in the sap) are
particularly effective against sap-feeding pests,
especially aphids and leaf miners. Contact materials
have a variety of uses, and stomach poisons are useful
for killing pests such as caterpillars, leaf beetles and
weevils. In some situations, fogs and fumigants may be
useful; in others, granules, pellets or sprays will be more
appropriate. Some pests (e.g. spider mites, and certain
aphids and thrips) have developed resistance to
pesticides, and this has limited the effectiveness of
many products. Whichever pesticide is selected, the
directions on the manufacturer's label should be
followed, and care taken to ensure that treatments are
applied appropriately, effectively and efficiently.
Some ornamental plants, such as Begonia ,
Calceolaria and Hydrangea , may be intolerant of
pesticides, and susceptibility sometimes varies from
cultivar to cultivar. In some cases, growth is checked,
perhaps imperceptibly; in others, tissue becomes
discoloured or distorted and, in extreme cases, affected
plants might be killed. Where information regarding the
safety of a pesticide to any particular plant species or
cultivar is lacking, or if doubt exists, a few plants should
be treated first and these later checked for signs of
phytotoxicity before larger-scale treatment is
undertaken. Young, tender plants are particularly
susceptible to chemicals; also, certain sprays
otherwise considered safe may have an adverse effect
on open blooms, causing a range of undesirable
symptoms such as speckling or overall discoloration of
tissue; spray damage of this type is well-known on
greenhouse-grown chrysanthemums. As a general rule,
spraying of open flowers should be avoided, not only
because of the risk of phytotoxicity but also to
safeguard pollinating insects which might be foraging
upon them. Further, spraying with pesticides should not
be undertaken during bright sunlight, the risk of
damage from excessive temperatures being particularly
serious in greenhouses and when plants are under
stress. In general, problems of phytotoxicity are more
likely to occur on protected plants than on those grown
outdoors.
Most pesticides recommended for use on ornamental
plants are available only to commercial growers.
However, some products are specifically formulated
and recommended for amateur use in private gardens.
These products will protect plants against the majority
of important pests. However, non-chemical methods
(see below) are often preferable and frequently just as
effective.
The application of pesticides in amenity areas poses
particular problems and is often impractical. Not only
are there increased risks of killing non-target species,
but potential hazards to the public must also be
considered. A few insecticides are specifically
formulated and recommended for control of pests in
amenity areas; such treatments are, of course, 'safe'
when used as recommended by the pesticide
manufacturers. Even so, on environmental grounds,
their use should be kept to the absolute minimum.
In some situations, both in amenity areas and
elsewhere, it is possible to use a biological control agent
rather than a chemical pesticide, and this has obvious
attractions. Examples include the application of the
bacterium Bacillus thuringiensis to kill caterpillars,
the use of predatory mites to combat spider mites, and
the release of parasitoid wasps to attack leaf miners on
greenhouse crops. Nowadays, various biological control
agents are available for use by both amateur and
commercial growers.
In nature, phytophagous insects, mites and so forth
are subject to attack by a wide range of natural enemies,
including a vast array of parasitoids and predators. Pests
also succumb to other naturally occurring controlling
agents, such as bacterial, fungal and viral diseases. Pests
of ornamental plants are no exception, and in many
situations their populations will remain below
economically important levels unless the balance of this
natural control is overturned. Although some pesticides
are intrinsically safe to beneficial insects and mites,
many have adverse effects upon them. It is prudent,
therefore, to restrict the use of chemicals and to ensure
that, when treatment with a pesticide is required, the one
chosen from the list of those available will have the
least deleterious impact on non-target organisms.
Recommendations relating to pest management often
vary according to local circumstances. They may also
differ in detail from country to country, if not from
region to region. Readers seeking information on pest
control or pest management, therefore, should refer to
information relevant to their regional or local
circumstances. On occasions, it might also be prudent to
seek expert advice.
Finally, an ability to identify pests correctly and to
recognize the symptoms of pest damage is an essential
starting point for good pest management. Knowledge of
the habits and biology of the various pests, and of the
risks they pose, is also required if correct decisions
concerning their possible control are to be made.
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