Transcript Level 2 Unit 205

 Pests
and Diseases in
Horticulture
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Level II Agricultural Business Operations
Session 8
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Group Task. – In pairs try to identify various
problems which may be a detriment to
healthy plant growth.
E.g. Weeds...........
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Weeds are often defined as a plant which is
growing in an unwanted position. For
example daisies growing within a wild flower
meadow may be fine, however growing in a
fine turf area they become a weed.
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Pests are animals that have a detrimental
effect on a plant. They mainly use the plant
as a source of food, either by eating parts of
it or sucking out the sap.
Pests can range in size from a large
vertebrate, like a deer or rabbit, to small
invertebrates like aphids, mites and
nematodes.
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Diseases are problems caused by other
organisms such as fungi, bacteria or viruses.
In severe cases they can cause the death of
the plant. Diseases are often spread by pests.
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A disorder is a problem caused by the
environment in which a plant is grown. An
example could be insufficient nutrients in the
soil to feed the plants. These problems are
often called physiological problems.
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Often people have wondered that no matter
how much time, effort and money is invested
in eradicating weeds they always seem to
return. This is generally because weeds are
extremely well adapted to the conditions in
which they grow, often more so than our
plants which may have evolved in very
different environments. Attempts have been
made to count the number of dormant seeds
in the soil and figures of 50000 per square
metre have been recorded.
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An annual is a plant that completes its lifecycle in 1 year. They
mostly germinate in spring or early summer and die at the start
of winter.
By their nature annual weeds survive only through their seeds
and the reasons they are so successful are:
Large numbers of seeds can be produced e.g. plantain can
produce 14000 seeds per plant.
Some can flower and set seed 3 times within a season e.g. nettle.
Some seeds can be carried significant distances by the wind e.g.
Dandelion
Some seed is forcibly ejected to spread it over a wide area. E.g.
Hairy bittercress.
Many seeds can lie dormant in the soil for many years until the
conditions for germination are present. Those conditions can be
caused by cultivation bringing the seeds to the surface. There is
a saying “One year’s seed – seven years’ weed”
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A perennial is an herbaceous plant with a life
of more than 2 years.
Many spread both by seed and vegetatively. It
is the vegetative growth that tends to be
most difficult to control as it is often
underground.
Many will regenerate from small pieces of the
plant left in the soil.
Many are resistant to herbicides. E.g.
horsetail
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Groundesel – Senecio vulgaris
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Hairy bittercress – Cardamine hirsuta
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Chickweed – Stellaria media
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Goosegrass/Cleavers – Galium aparine
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Sheperd’s Purse – Capsella bursa – pastoris
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Ground elder – Aegopodium podagraria
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Nettle – Urtica dioica
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Creeping Buttercup – Ranunculus repens
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Greater Plantain – Plantago major
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Dock/Dalkin - Rumex obtusifolius
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Pests come in many shapes and sizes. Most
of the smaller pests are insects which are by
far the most numerous species on earth.
Common pests affect plants in various
different ways with varying levels of
seriousness.
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Many birds can have a detrimental affect on
plants, in particular fruits and vegetables
involved in production.
The following birds are particular pests :
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Bullfinch
Bullfinches will
systematically eat the
buds of fruit and
ornamental trees and
shrubs, seriously
reducing the flowers
and subsequent fruit.
Plants are most at
risk from midwinter
until spring.
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Wood pigeon
Wood pigeons will
take seeds of peas
and beans, young
seedlings, and eat
the leaves of
brassicas. They are
most active in
spring and early
summer.
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House Sparrow
House sparrows are a
particular nuisance in
urban areas. They
feed on seeds but
will attack and
damage all parts of a
wide range of plants.
They are most active
from June to
December.
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Rabbits will eat most tender parts of plants,
and leafy vegetables are particularly at risk.
They will also strip the bark from young trees
which can cause the tree to die.
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Slugs and snails will eat most parts of vegetables and
herbaceous plants, with the young growth in spring
particularly vulnerable. Slugs will also eat seeds and tubers,
and maincrop potatoes are often badly damaged. They are
most active at night and in humid conditions.
Symptoms – Irregular holes in leaves and other parts of the
plant. Slime trails can be seen on soil and hard surfaces.
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Aphids are one of the commonest garden pests. There are
many different species including greenfly and blackfly.
Some species are particular to one plant but others will
attack a range of plants. Some are winged and can travel
significant distances on the wind. They feed on the sap of
plants by inserting stylets into the plant tissue and sucking
out the sap. In addition to directly attacking plants aphids
are responsible for spreading some viruses. Their breeding
potential is enormous. The females give birth to live young
which mature in about a week and within a season one
female could theoretically have millions of descendants.
Symptoms – The aphids can be seen, usually on the new
growth of plants which can be weakened and distorted.
They secrete a sticky substance called honeydew which
can be infected by sooty mould which is a blackish fungal
infection
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Whiteflies are small, sap sucking insects. There are
many species but 2 of the most troublesome are
greenhouse whiteflies and cabbage whiteflies.
Greenhouse whitefly mainly attack glasshouse plants
like tomatoes and cucumbers, and can be difficult to
control as they breed rapidly in the warm conditions.
Although they are short lived the females can lay up
to 200 eggs. These eggs hatch and pupate as scales
before the adult emerges. The reproduction cycle is
3-4 weeks. The cabbage whitefly is hardier and
survives outside on brassicas.
Symptoms – The whitefly can be seen, usually on the
underside of leaves. If disturbed they will often fly off
the plant in a cloud. Like aphids they secrete
honeydew that can attract sooty mould.
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Vine weevil is a beetle that attacks a wide range of plants, both indoors
and outdoors, but especially plants grown in containers.
It is one of the most common and devastating garden pests. The adult
weevils eat plant leaves during spring and summer, but it is the grubs
that cause the most damage over autumn and winter when they feed on
plant roots, causing wilting, and often plant death.
Plants growing in pots or other containers, outdoors or under cover, can
be severely damaged by vine weevil grubs. Plants growing in the open
ground are less susceptible, although the grubs can kill strawberries,
primulas, polyanthus, Sedum, Heuchera and young yew plants.
The adult beetles feed on the foliage of many herbaceous plants and
shrubs, especially Rhododendron, evergreen Euonymus, Hydrangea,
Epimedium, Bergenia, Primula and strawberry.
Symptoms – The larvae feed on the roots of plants so the first indication
of anything wrong could be the collapse and death of the plant. Adult
vine weevil will feed on the leaf of many different plant species.
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Diseases are caused by fungi, bacteria or
viruses, which are collectively known as
pathogens.
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Fungi are related to plants but they do not
photosynthesise. They derive their food from
dead or living organic matter such as other
plants. Some fungi are specific to certain plants
but others attack a range of plants.
They spread by means of spores which are
carried by wind or water, and which can survive
in soil, seeds or tubers. Fungicides work by
killing the spores or preventing them from
germinating.
The damage fungi cause may be localised or it
may affect, and eventually kill, the whole plant.
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Powdery mildew is a fungal disease that can
affect fruit like apples, vegetables like peas or
ornamentals such as roses. There a large number
of different types of powdery mildew, although
the symptoms and treatment are basically the
same. The disease is spread by spores which can
travel long distances in the wind.
Symptoms – Leaves, stems and buds are coated
with a white powdery substance. The leaves may
turn yellow and drop prematurely. Growth may
be retarded and distorted.
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This is a widespread fungal disease affecting
many varieties of fruit, vegetables and
ornamentals. It primarily attacks buds and
fruits, rendering the fruit inedible and can
also affect stored fruit. It thrives in damp and
overcrowded conditions where it spreads
rapidly from plant to plant.
Symptoms – A fluffy grey mould develops on
the infected parts which then turn brown and
rot.
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There are many different species of this fungal
infection that attacks a wide variety of plants
including fruit, vegetables and ornamentals. One
of the most common is rose rust. Rust takes
away nutrients from the host plant causing a
general weakening of growth. The spores
overwinter on fallen debris.
Symptoms – orange/brown pastules form on the
undersides of leaves and yellowish spots can
form on the upper surface. Leaves may wither
and fall pre maturely.
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Bacteria are single celled microorganisms that
can infect plants through wounds. Bacteria
reproduce by cell division and the numbers
can multiply very quickly under warm
conditions. Bacterial diseases can be difficult
to control as fungicides are not always
effective.
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Bacterial canker is a disease caused by two closely related
species of bacteria that infect the stems and leaves of
plums, cherries and related Prunus species. It is one of the
few important plant diseases caused by bacteria in the UK.
Cankers begin to form in mid-spring and soon afterwards
shoots may die back. Shotholes appear on foliage from
early summer.
Symptoms - On stems and spurs: Sunken, dead areas of
bark develop in spring and early summer, often
accompanied by a gummy ooze. If the infection spreads all
round the branch it will die rapidly. On leaves: Small brown
spots appear which are often round and fall out later to
leave holes – as if the leaf had been hit by shotgun pellets,
leading to the popular name of ‘shothole’
Colin McKnight
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Fireblight is a bacterial disease which kills the shoots of apples
and pears and their ornamental relatives, giving the plant the
appearance of having been scorched by fire. Fireblight infects
only those members of the Rosaceae in the sub-family
Pomoideae; apples, pears and related ornamentals including
Cotoneaster, Sorbus, Crataegus (hawthorn), Photinia (syn.
Stransvaesia) and Pyracantha. Fireblight does not infect stone
fruits, such as plums, cherries, peaches and nectarines (Prunus
spp.) Expect to see damage from late spring until autumn.
Symptoms - Blossoms wilt and die at flowering time. A slimy
white liquid may exude from infections in wet weather. Shoots
shrivel and die as the infection spreads down the inner bark.
During the short period of active spread, the outer wood is
stained a foxy brown colour when the infected bark is peeled
back. Cankers (areas of dead, sunken bark) on branches,
especially where infected shoots join larger branches
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Viruses are microorganisms that live as
parasites in other living tissue. The common
cold is a virus affecting humans. The virus
can affect the whole plant and is likely to be
transmitted by any vegetative reproduction.
There is usually no cure for a viral infection
and the plants affected are best dug up and
burned.
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Camellia yellow mottle virus causes yellow and creamywhite blotches on leaves of camellias. It may also cause
discoloured areas within the petals (flower breaking). This
virus has little effect on vigour.
Symptoms - Affected leaves develop green and yellow
patterns. The discoloured areas are often bright yellow (or
occasionally even creamy-white) and contrast strongly
with the adjacent dark green tissue. The yellowing may
take the form of irregular large blotches or smaller flecks.
Discoloured areas within the petals (known as flower
breaking) have also been reported, but this symptom is
much less common. The symptoms are often confined to a
small number of branches. They may persist from year to
year, vary from one year to another, or even disappear
completely over time.
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Pelargonium viruses are virus diseases that
affect pelargoniums. They may lead to
stunted growth or cause strange flower or
leaf markings. One is a notifiable quarantine
organism (tomato ringspot virus)
Symptoms - White streaks in the flowers,
known as 'breaks‘. Yellow mottling patterns
on the leaves. Sometimes leaves develop line
patterns, or ringspots. Plants may be stunted
with a general lack of vigour
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Disorders are plant problems that are not
caused by pests or diseases but by some
problem in the environment in which the
plant is being grown. Theses are called
physiological disorders. Disorders can be due
to a lack of plant nutrients or can be caused
by the climate.
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Frost can cause plant cells to freeze and, as water expands on freezing,
the cells can be ruptured. The main damage from frost occurs either
with the first frosts of autumn or the late frosts of spring. In autumn any
non-hardy plants such as summer bedding will blacken and die in the
first frosts. Late spring frosts are classed as much more serious as they
can cause damage to young shoots, buds and flowers. Fruit trees are
particularly susceptible where buds can be killed and the subsequent
crop ruined, and some early flowering shrubs such as camellia,
ceanothus and magnolia. Damage can also be done by rapid thawing
following a frost. It is for this reason that some plants should not be
placed on an east all where they will get the morning sun.
Symptoms – The foliage is scorched, it turns brown and brittle,
particularly at the edges, although the whole leaf may be discoloured
and wither. Small plants may be killed. Buds can be damaged or killed
thus reducing the production of flowers and fruit. Blossom and fruitlets
may drop. The skin of the fruit that is produced may be cracked or
rusted.
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Avoid planting in a low lying or hollow area.
Choose frost hardy or late flowering varieties.
Provide protection for plant foliage e.g.
Cloche, straw etc.
Do not plant out seedlings until danger of
frost has passed.
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Wind can adversely affect plants in a number
of ways:
Direct damage by breaking stems and
branches, blowing off fruity and damaging
flowers.
Increasing the rate of water loss.
Lowering the temperature around the plant
and causing wind scorch.
Discouraging pollinating insects.
Spreading salt damage in coastal areas.
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In winter, evergreen plants are prone to wind
scorch (also known as leaf scorch). This is caused
by cold winds and poor soil conditions resulting
in scorched, brown, dry leaves.
Symptoms - Scorched leaves have brown,
desiccated edges or may be entirely brown and
dry. Wind scorch may be worst in exposed areas
or on the windward side of the plant. Largeleaved evergreens are affected worse than smallleaved plants, and pot plants are at particular risk
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Choice of a sheltered site if possible.
Provision of a shelter belt or windbreak.
Choose hardy varieties of plants.
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The presence of water is fundamental to the
healthy survival of any plant species. Water is
taken up by the roots of the plant and lost by
transpiration through he leaves. About 95% of
the water taken up is lost in this way. To the
extent that the loss is greater than the uptake the
plant is likely to suffer damage. For short periods
such as on a hot day the plant will soon recover
but a continuous imbalance will soon cause
permanent damage.
Symptoms – The foliage of the plant will start to
wilt and turn brown. If not corrected the leaves
may fall and the plant will wilt and die. Flowers
and fruit may fail to set.
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Watering plants at critical times, including dry
spells.
Mulching will help to reduce water loss by
evaporation.
Increase the water holding capacity of the soil
by adding organic matter such as compost.
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Water logging occurs when the pore space within the soil is filled with
water. This stops oxygen reaching the roots, which is required for
respiration, and prevents the escape of carbon dioxide which is given off
by respiration.
Few garden plants will survive water logging or flooding. Prolonged
periods of sitting in ground saturated with water causes yellow leaves,
root rot and death.
Symptoms - The first symptoms appear on the leaves. This includes
yellowing or decay between the veins, resulting in soft areas at the base
or centre of the leaf. There may be dark areas along the midrib, and
areas within the leaf go brown, especially on evergreen leaves. The plant
may also look like it is short of water, even wilting. A root sample will
show blue-black roots, a typical sign of water logging that may be
accompanied by a sour, rotting smell. Roots may rot away completely,
with few remaining. Damaged roots will be blackened and the bark may
peel away. Shoots may die back due to a lack of moisture (the roots
cannot supply water to the leaves) and bark peels off the shoots easily.
Herbaceous plants may fail to sprout in spring, or leaves may open and
then die. Plants may be stunted, or even die. Some plants suffer from a
condition called oedema.
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Improving the soil structure by various
methods such as verti draining.
In more serious cases drains may need to be
installed.
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Other threats include – Humidity
Heat
Light/Shade
Nutrient deficency
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Cultural control covers all the activities
designed to ensure that plants get the best
protection against many problems.
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Removal by digging or rotavating.
Hoeing and hand weeding.
Mulching, membranes.
Ground cover planting.
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Can be difficult to implement.
Emphasis placed on prevention instead of curing.
Plant and maintain healthy plants – soil, suitable plants,
aftercare, monitoring, cleanliness, use resistant plants.
Encourage natural predators
Physical barriers and traps – Fencing, netting, collars,
grease bands, crop covers, pheromone traps, sticky traps,
beer traps etc.
Crop rotation
Time of sowing
Companion planting – Marigolds in greenhouse to deter
whitefly. Garlic under roses to prevent blackspot. Mint
around brassicas to deter the cabbage white butterfly.
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What do you think biological control involves?
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Biological control is the use of natural
enemies to control pests, they have become
increasingly popular due to the environmental
concerns raised over chemical use and the
subsequent restrictions on these.
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What are the advantages and disadvantages
of these and what considerations must be
taken into place?
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Many only effective in a closed environment
like a glasshouse.
Chemicals can kill both pest and predator.
Timing of use is critical.
Predator may need several re-introductions
throughout the season.
https://www.youtube.com/watch?v=Hj3Dwim
xvvY
Most common is ladybird used to control
aphids.
Pheromone traps.
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3 main groups – Herbicides
Insecticides
Fungicides
The term pesticide covers all 3 groups.
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Safety precautions.
Read label to ensure suitability
Store in a safe place
Keep it in its original container
Apply at correct rate.
Spray during correct conditions
Do not eat, drink or smoke during application.
Avoid contact with skin or eyes.
Do not inhale spray or fumes etc
Set up an exclusion zone.
Wash hands thoroughly after use.
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Herbicides act in differing ways.
Contact – these kill or damage any plant that
they touch. They are effective against annuals
but not so much perennials, why?
Translocated/systemic – These are absorbed
by the plant and distributed around it in the
sap. Effective against all weeds.
Residual – These are held in the soil and
prevent germination of seeds.
Selective -These affect certain plants but not
others.
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These are used to control pests.
These also act in differing ways;
Contact – Pest will be killed by contact from chemical or
from eating the foliage of a plant which has been sprayed.
Can be difficult to access pests living on underside of the
leaf, however they do not enter the plant.
Systemic – the chemical is absorbed by the plant and
distributed around it in the sap. A pest is then killed when
it sucks the sap or eats the foliage.
Soil acting – Control soil borne pests.
Selective – Only effective on certain target species.
Organic – Derived from plants or naturally occurring
chemicals such as sulphur. Break down quickly into
harmless substances.
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Fungicides are used to prevent or cure
diseases. The diseases may be caused by
fungi, bacteria or viruses, they too act in
differing ways ;
Preventative – The fungicide coats the foliage
of the plant and prevents the disease from
entering. Most fungicides are preventive.
Systemic – These are absorbed by the plant
and transported throughout it killing the
disease.
Questions???