|Figure 14.1 Red spider
mite symptoms on palm
A small selection of important mammal pests is included here.
The rabbit (Oryctolagus cuniculus)
The rabbit is common in most countries of central and southern Europe.
It came to Britain around the eleventh century with the Normans, and
became an established pest in the nineteenth century.
The rabbit may consume 0.5 kg of plant food per day. Young
turf and cereal crops are the worst affected, particularly winter varieties
that, in the seedling stage, may be almost completely destroyed. Rabbits
may move from cereal crops to horticultural holdings. Stems of top fruit
may be ring barked
by rabbits, particularly in early spring when other
food is scarce. Vegetables and recently planted garden-border plants
are a common target for the pest, and fine turf on golf courses may
be damaged, thus allowing lawn weeds, e.g. yarrow, to become
The rabbit’s high reproductive ability enables it to maintain
high populations even when continued control methods are in operation.
The doe, weighing about 1 kg, can reproduce within a year of its birth,
and may have three to five litters of three to six young ones in 1 year,
commonly in the months of February to July. The young are blind
and naked at birth, but emerge from the underground ‘maternal’ nest
after only a few weeks to find their own food. Large burrow systems (warrens),
penetrating as deep as 3 m in sandy soils, may contain as
many as 100 rabbits. Escape or bolt holes
running off from the main
burrow system allow the rabbit to escape from predators.
Rabbit control is, by law, the responsibility of the land owner. Preventative
measures, available to both amateur
horticulturists are effective. Wire fencing,
with the base 30 cm underground
and facing outwards, represents an effective barrier to the
pest, while thick plastic sheet guards
are commonly coiled round the
base of exposed young trees (see Figure 16.2). Repellant chemicals, e.g. aluminium ammonium sulphate,
may be sprayed on bedding displays
and young trees.
Small spring traps
placed in the rabbit hole, winter ferreting
placed at the corner of a field to catch herded rabbits are methods
used as curative
are used on large horticultural
holdings by holders of gun licences.
is an effective method, but must be applied only by trained
operators. Crystals of powdered sodium cyanide
are introduced into the
holes of warrens by means of long-handled spoons or by power operated
machines. On contact with moisture hydrocyanic acid is released as a
gas and, in well-blocked warrens, the rabbits are quickly killed. Care is
required in the storage and use of powdered cyanide, where an antidote ,
amyl nitrite, should be readily available.
Pest . A mammal, bird, insect, mite or
nematode that is damaging to plants.
a flea-borne virus disease of the rabbit, causing a swollen
head and eyes, was introduced into Britain in 1953, and within a few
years greatly reduced the rabbit population. The development of weaker
virus strains, and the increase in rabbit resistance, has combined to
reduce this disease’s effectiveness in control, although its importance in
any one area is constantly fluctuating.
The brown rat (Rattus norvegicus)
The brown rat, also called the common rat, is well known by its darkbrown
colour, blunt nose, short ears and long, scaly tail.
Its diet is varied; it will eat seeds, succulent stems, bulbs
and may grind its teeth down to size by the unlikely act of
gnawing at plastic piping
and electric cables. A rat’s average annual
food intake may reach 50 kg, a large amount for an animal weighing
only about 300g.
This species has considerable reproductive powers. The
female may begin to breed at 8 weeks of age, producing an average of six
litters of six young ones per year. Its unpopular image is further increased
by its habit of fouling the food it eats, and by the potentially lethal human
bacterium causing Weil’s disease,
which it transmits through its urine.
gardeners are able to use products containing aluminium ammonium sulphate
to deter rats. Sonic
sometimes used to disturb the animal and provide a round-the-clock
with rat poison should be performed by trained operatives.
This method is best achieved by a preliminary survey of rat numbers in
buildings and fields of the horticultural holding, and by the identification
of the ‘rat-runs’ along which the animals travel. Baits containing a
mixture of anticoagulant
poison and food material such as oatmeal are
placed near the runs, inside a container that, while attracting the rat,
prevents access by children and pets. Drainage tiles or oil drums drilled
with a small rat-sized hole often serve this purpose. The poison, e.g. difenacoum,
takes about three days to kill the rat and, since the other
rats do not associate the rat’s death with the chemical, the whole family
may be controlled. The bait should be placed wherever there are signs
of rat activity, and repeated applications every three days for a period of
three weeks should be effective.
Strains of rat resistant to some anticoagulants are found in some areas,
and a range of chemicals may need to be tried before successful control
is achieved. The poison, when not in use, should be safely stored away
from children and pets. Dead rats should be burnt to avoid poisoning of
The grey squirrel (Sciurus carolinensis)
This attractive-looking 45 cm long creature was introduced into Britain
in the late nineteenth century, at a time when the red squirrel population was suffering from disease. The grey squirrel became dominant in most
areas, with the red squirrel surviving in isolated areas such as the Isle of
The horticultural damage caused by grey squirrels varies with
each season. In spring, germinating bulbs
may be eaten, and the bark
of many tree species stripped off (see ring barking). In summer, pears, plums
may suffer. Autumn provides a large wild food
source, although apples
may be damaged. In winter, little
damage is done. Fields next to wooded areas are clearly prone to squirrel
Squirrels most commonly produce two litters of three young
ones from March to June, in twig platforms (dreys
) high in the trees.
The female may become pregnant at an early age (6 months). As the
squirrels have few natural enemies, and this species lives high above
ground, control is difficult.
horticulturists may need to reduce
grey squirrel numbers. During the months of April–July, when most
damage is seen, cage traps
containing desirable food, e.g. maize seed,
reduce the squirrel population to less damaging levels. Spring traps
placed in natural or artificial tunnels achieve rapid results at this time
of year if placed where the squirrel moves. Professional
are able to use poisoned bait
containing a formulation of anticoagulant
chemical, e.g. warfarin,
when placed in a well-designed ground-level hopper
(one hopper per 3ha). This can achieve successful squirrel
control without affecting other small wild mammal numbers. In winter
and early spring, the destruction of squirrel nests by means of long poles
may achieve some success.
The mole (Talpa europea)
|Figure 14.2 Mole hill in grass
The mole is found in all parts of the British
Isles except Ireland.
This dark-grey, 15 cm long
mammal, weighing about 90 g, uses
its shovel-shaped feet to create an
underground system 5–20 cm deep and up
to 0.25 ha in extent. The tunnel contents
are excavated into mole hills (see Figure
14.2). The resulting root disturbance
grassland and other crops causes wilting,
and may result in serious losses.
In its dark environment, the
solitary mole moves, actively searching for
earthworms, slugs, millipedes and insects.
About 5 hours of activity is followed by
about 3 hours of rest. Only in spring do males and females meet. In
June, one litter of two to seven young ones are born in a grass-lined underground nest, often located underneath a dense thicket. Young
moles often move above ground, reach maturity at about 4 months, and
live for about 4 years.
Natural predators of the mole include tawny owls, weasels
and foxes. The main control methods are trapping
and poison baiting,
usually carried out between October and April, when tunnelling is
closer to the surface. Amateur
use pincer or half barrel traps
placed in fresh tunnels and inserted
carefully so as not to greatly change the tunnel diameter. The soil must
be replaced so that the mole sees no light from its position in the tunnel.
The mole enters the trap, is caught and starves to death. In serious
mole infestations, trained operators use strychnine
salts mixed with
earthworms at the rate of 2 g ingredient per 100 worms. Single worms
are carefully inserted into inhabited tunnels at the rate of 25 worms per
hectare. DEFRA authority is required before purchasing strychnine, a
highly dangerous chemical, which must be stored with care.
Deer may become pests in land adjoining woodland where they
hide. Muntjac and roe deer ring-bark
trees and eat
succulent crops. High fences and regular shooting may be used in