Life cycle of two pests
Life cycle of two pests
There are over 500 species in
Britain, fortunately only a few are
most are specific to one or two
The Peach - potato aphid (Myzus
persicae) is the green one which is
most often seen on a wide range
of plants, but can range in colour
from yellow, all shades of green, to
pink, red and almost black.
There are root aphids which
attack below ground and with
a severe infestation will kill
the plant by removing the
sap before it can rise up the
stem. They are white and
waxy, giving them the
appearance of a fungus.
The usual symptom of their presence is distorted, weak
growth of leaves and shoots.
A large infestation can cause roots to reduce in size due
to the sucking activity of the aphids increasing the
transpiration stream, so the plant requires fewer roots to
supply the volume of water by normal means.
When their numbers decrease the plant suffers.
They can be carried for hundreds of
miles by wind or air currents, and can
transfer viruses as they move to other
They need to suck up copious
amounts of sap to obtain the small
amounts of protein it contains.
The excess, which contains sugars is
flicked from their bottoms and is given
the appetizing name of honeydew.
This sticks to leaves and can be
colonised by Sooty Mould, which
reduces the amount of light reaching
the photosynthesising cells, so further
weakening the plant.
They are attracted by the pale
yellowish-green of young shoots
where they know there is plenty of sap
in tissues which are easily penetrated.
One species infests most Lime trees
where they are joined by Scale insects
which add to the problem - the honeydew
can usually be seen on parked cars and
plants below them.
Some colonies of Ants 'herd' the aphids
and collect the honeydew to feed their
larvae; they protect the aphids and carry
them to overwinter in their nests.
In spring and summer only females are present
reproducing asexually by a process known as
parthenogenesis, giving birth to live young.
In the autumn, males are produced and after mating the
females lay eggs which remain through the winter in
The population can double in 4 - 6 days;
starting with one aphid, after one year of uninterrupted
reproduction in perfect conditions would produce 250
million tons if none died!
This means that they are a good source of food to other
creatures including Ladybirds and their larvae,
lacewings, hoverfly larvae and parasitic wasps.
Where only a few are present they can be
rubbed off affected shoots, after a while natural
predators will arrive and remove them.
A hose with good force can be used to dislodge
them from tough-leaved vegetables.
A spray prepared from a couple drops of
washing-up liquid to a gallon of water as an
acceptable organic method of control; so are
insecticidal soaps made from plant fatty acids.
Avoid spraying in sunshine to prevent scorching
Biological controls need a constant supply
to survive, so there will always be a lowlevel presence, hopefully these will be on
nearby wild plants. Ladybirds are nocturnal
so if they are feeding during the day the
number of aphids may be low.
For chemical control use pyrethroids or
bifenthrin - spray as late in the day as
possible to avoid Ladybirds and other
There is evidence that Myzus persicae are
developing resistance to the pyrethroids
and Primocarb so it is best to vary the
chemicals used to reduce the chances of
An acceptable organic spray is
made from an extract of the Neem
tree called Azadiractin
Companion planting using partner
plants which deter the aphids, eg.
Borage to deter Black Bean
Slugs and Snails are molluscs of the class
Gastropoda which literally translated is 'stomach
Gastropods form the second largest class in the
animal kingdom, the largest being insects.
Of the 29 species in Britain a few are
carnivorous, but most live on living and decaying
plant tissue; usually the plants we like to look at
or eat ourselves!
Instead of a shell like the snails,
slugs have an internal horny plate
covering their breathing cavity.
There is a range of colours and
sizes of slug depending on the
species. The Field Slug is 2cm and
grey, while the Round Back Slug
can be 5-10cm, black or brown
and in some cases can have an
orange colour on their foot.
They feed by rasping ragged holes
in flowers, leaves, stems, roots
and seeds, with young plants the
leaf feeding can kill.
Below soil level some species
attack root crops - the small Black
Keeled Slug being particularly
destructive, especially to potatoes
and the bases of plant stems.
Many species spend most or all of
their life underground and those
seen are only a small proportion of
Slugs begin to move, hatch, feed,
and lay eggs when the temperature
is above 5 °C.
During dry and cold conditions they
remain deep in the soil.
The wetter weather and milder
winters of late has been very
beneficial, and most gardeners have
noticed an increase in their numbers.
They are usually nocturnal, but will
venture out on dull, damp days.
There are three stages in the life cycle:
eggs, immature stage and adults - they
can overwinter in any stage.
They are hermaphrodite having both
male and female organs, so every
individual can lay eggs - up to 300 each
in batches of 10 to 50 in moist, but not
waterlogged, crevices; sometimes down
the sides of pots.
One individual has the potential to
produce about 40,000 offspring.
Eggs are gelatinous, watery,
about 3 - 4mm across and usually
spherical like tapioca.
The period of development of the
eggs varies depending on the
temperature, during warmer
weather they hatch after 10 days,
but this can be up to 100 days in
After hatching the slug matures in
less than a year and can live for
two or more years.
There are many suggestions to kill or deter
this pest, but even the most diligent
collection regime has been shown to have
little effect on the damage caused.
The best thing is to try and cope with them
by following some general hygiene
Remove their hiding places and spots where they lay
eggs, eg. rotting boards, logs, stones dead leaves and
Place compost heaps away from vulnerable plants.
But don't be too tidy as Ground Beetles which feed on
the eggs, like to hide during the day as well, large stones
and pebbles will do for them.
Another creature which appears to eat the eggs is the
New Zealand Flatworm -.
use traps, eg. stones, boards, upturned pots
empty grapefruit skins or wet sacking, the slugs
take cover underneath and can be collected.
They will also lay their eggs here so they can be
destroyed as well.
go slug hunting at dusk and chop them up or
put them in hot water, this is the most effective
method of reducing their numbers, but the most
destructive species do not emerge often. The
slimy bodies are not very pleasant to handle so
use tweezers, chopsticks
Ordinary table salt is lethal to slugs, but overuse is
detrimental to plants and other creatures. It is probably
best to drop them into a container of this, rather than
sprinkling it about.
A tablespoonful of oats acts as an attractant when
placed beside more favoured plants. The slugs can be
collected and destroyed.
attract hedgehogs into the garden with dog food (not
bread it clogs their digestive system and milk is bad for
young hedgehogs). Keep them there with a concealed,
dry home with straw bedding and don't light bonfires
without checking for sleeping 'hogs.
beer traps should have the entrance about
3cm above soil level to prevent Ground
Beetles falling in - put a few twigs inside to
help any which do fall in, to climb out. Beer
cans can be quite effective,
An alternative to beer is a mixture of sugary
water and yeast or milk, but the best bait is
said to be stout .
Slugs are also partial to cat and dog food, so
this too makes a suitable bait.
A home-made trap can be constructed from
an empty margarine or ice-cream tub with a
hole cut in the side near to the top - the lid
makes escape more difficult and stops the
trap filling up with rain water.
researchers in Hawaii have found that
a 1 to 2% solution of caffeine will kill
slugs and a 0.1% solution will deter
them if is sprayed on leaves. However,
this latter strength solution also
scorched the young leaves of
frogs, toads, hedgehogs, some
beetles and their larvae, centipedes,
parasitic flies, birds, chickens, and
ducks are natural enemies. Attract
these creatures by providing shelter
like a thick hedge
a dry mulch will reduce slug activity, this is
achieved using a dutch hoe in dry weather.
Alternatives are grit, sawdust, cocco shells,
weathered cinders, wood ash or crushed egg
However their protective slime can allow them to
crawl over a razor blade or sharp glass, so these
methods are of limited success at best and are
usually wishful thinking!
Fito Slug Stoppa granules form a
rough barrier and absorb slime so
make it difficult for slugs to move over
them, but are quite expensive.
Diatomaceous Earth is a dry
granular substance made up of
fossilised algae. It is applied as a
barrier to exclude the slugs. It loses
its effectiveness when wet, but
regains it after drying out.
a copper wire or strip placed in a circle
around the area is said to deter by creating
a micro-current as the slug touches it.
Check for the presence of slugs or their
eggs first and destroy - there is no point in
trapping them inside!
Strips around pots could also be
decorative. A self-adhesive copper tape is
available in some garden centres or online.
There is also a woven mesh which can be
erected as a small fence, but it must be in
contact with the soil along its full length
otherwise they will crawl underneath.
cut the bottom off a plastic drinks bottle
and remove the cap, to form a protective
cylinder around vulnerable young plants.
a slick of petroleum jelly around the top
of containers prevents them crossing to
the contents, but makes handling the pots
difficult and it becomes covered with dust
for use when on slug patrol, make a halfand-half mixture of vinegar and water in
a handsprayer. One squirt should kill
Also a 1 : 3 mixture of household
ammonia in water should work.
a biological control is the nematode (eel worm) Phasmarhabditis
hermaphrodita which occurs naturally and is used in Slugsure.
They invade the slug and bacteria which they carry cause the slug to
stop feeding, go underground and die.
As they decompose the eel worms reproduce.
This natural control is less effective on surface dwelling species
as the eel worms live in the moist conditions below ground, but they
are the best treatment for the underground species which attack root
Nematodes are unaffected by wet weather. They remain active for
about 6 weeks, and need a minimum temperarure of 5°C.
Another brand is Nemaslug (Phasmarhabditis hermaphrodita),
which is available by mail order or on-line. They can be ordered
between March and October, and keep in the fridge for a few weeks
slug pellets, said to be safe by their
manufacturers if sprinkled thinly around.
They are dangerous to pets if they find the
Birds are not likely to eat them directly
and they do not eat the corpses, but
slightly affected slugs may be eaten and
some studies show that the bird's fertility
may be reduced.
The same chemicals, usually
metaldehyde, can be applied as a
Another slug bait is one containing ferric
phosphate which works best in moist
It is considered to be organic and although
it is less effective than metaldehyde, it can
be used where crops are grown and is not
hazardous to pets.
It degrades over time in the soil to iron and
some species or varieties of vulnerable plants
with thicker leaves are said to be resistant.
sacrificial plants such as lettuce planted near
to vulnerable ones, may draw the slugs away
and keep them interested for long enough to be
picked up and removed.
keeping vulnerable plants such as Hostas in
drier conditions makes the leaves tougher and a
bit less attractive to the slugs.