Diseases

Question 1

What is plant disease and what can it do to plants?

Answer 1

Damage caused by microscopic disease causing agent such as fungi, bacteria or virus (pathogens).
May result in low yield of crops, plant death, or disfigurement.
EG. Irish potato famine - millions died.

Question 2

What is Botrytis?

Answer 2

A fungus causing grey mould.
Fluffy light grey fungal mass on leaves, stems, fruits, flowers & buds.
Fuzzy grey mould.
Leaves, stems and petals may start with dead brown patches.
Plants grown under glass can be particularly susceptible as conditions are humid and air circulation is limited because plants are grown close together.
Affects strawberries, grapes, blackberry, courgette, lettuce, tomato, Chrysanthemum, cyclamen, pelargonium, rasberry.

Question 3

What conditions does Botrytis thrive in and how does botrytis spread?

Answer 3

Requires wounded tissue for infection to spread between different plant species.
Fungal spores enter through a wound or can infect plants when under stress.
Damp conditions are essential.
Broken stems or injured leaves.
Seedlings in moist cool conditions.
Leaves damaged by over fertilisation.

Question 4

How to control & prevent botrytis?

Answer 4

Regular plant checks to ensure infections do not get established.
Heat and ventilate glasshouses to prevent high humidity conditions.
Do not overcrowd plants
Water in the early morning hours and avoid watering overhead and spreading spores via water splash.
Hygiene is very important, especially uner glass.
Remove dead plant material.
Isolate infected plants.
Mulch to prevent water splash.
Fleece between plants to prevent spore spread.
No fungicides are approved for use against grey mould by gardeners.

Question 5

What is strawberry powdery midlew?

Answer 5

A fungal disease affecting strawberries.

White or grey dusty coating on shoots and leaves.
Distorted leaf growth.
Leaves curl upwards.
Deformed fruit/reduced crop.
Mature fruits when infected may show white powdery mycelial growth.
Mouldy tasting fruit.

Question 6

Does powdery mildew have a wide host range? How does powdery mildew spread? How does it over winter?

Answer 6

Powdery mildew usually have narrow host ranges comprising of just a few related plants.
Thrive where conditions are hot and dry, where there is dry root zone and humid environment around the leaves.
Favours dry conditions where plants are overcrowded with reduced air circulation.
Spores are spready far and wide by the wind or by water splash.
Can over winter on living plant or plant debris.

Question 7

How to control and prevent spread of powdery mildew?

Answer 7

Hygiene - remove spores, dead foliage in winter.
Avoid water stress - water regularly and avoid overcrowding.
Avoid watering overhead and spreading spores via water splash.
Ventilate
More problematic in greenhouses and high tunnels.
Prune out infected growth as soon as see symptoms.
Burn/destroy infected material.
Incorporate OM to soil in autumn and mulch in spring to avoid water stress.
Don’t over feed plants and encourage sappy growth hat is more vulnerable to infection.
Grow in cool locations.
Grow resistant cultivars.
SB plant invigorator as a liquid concentrate creates a physical barrier against spore infection. Applied as a foliar feed.

Question 8

What is rose blackspot?

Answer 8

A fungal disease that affects roses.
Purple or black spots appear on leaves.
Leaf tissue may turn yellow around the spots.
Premature leaf drop.
Can significantly reduce plant vigour.
Also purple/black spots on stems.
Overwinters on stems or fallen leaves then infects in spring.

Question 9

How does Rose Black spot spread?

Answer 9

Produces spores in the black spot lesions on the upper leaf surface.
These spread in water to infect new areas of growth.
Wet conditions are required for the disease to build up.
Spores overwinter in structures on fallen leaves and also in dormant infections on young stems and buds.
Spread is worse in warm wet weather.
Can be spread by hands, clothing, tools and rain splash.

Question 10

How to control and prevent Black Rose Spot?

Answer 10

Collect and destroy fallen leaves in the autumn.
Alternatively bury them under a layer of mulch to prevent rai splashing spores up in spring.
Prune out all stems with visible symptoms in spring before leaves appear.
Grow resistant varieties - eg. ‘Royal William’ ‘or ‘New Dawn’.
Dig in plenty of Organic matter at planting andkeep plants well watered and fed throughout the growing season.
Strong healthy plants will generally resist attack better than those that are weak.
Chemical control - Fungus Fighter (Tebuconazole) as a liquid concentrate or Fungus clear ultra (Triconazole) as ready to use spray.

Question 11

What 3 groups can diseases be classified into?

Answer 11

Fungi
Bacteria
Viruses

Question 12

Disease represents the interaction between 3 different factors. What are they?

Answer 12

1. Susceptible host plant.
2. Presence of pathogen
3. Environmental conditions.

Question 13

Give some examples of general disease symptoms?

Answer 13

Because disease pathogens are generally microscopic, symptoms are usually -

• Changes in colour of the plant tissue
• Necrosis of tissue
• Leaf spots
• Stunted growth.
• Distorted growth.
• Wilting
• Decreased yield
• Powdery coating
• Leaf mottling
• Rapid death and collapse.
• Oozing cankers
• Premature leaf fall

Question 14

What things are helpful to know about a disease, in order to help prevent it?

Answer 14

Do spores over winter and how - on living or dead plant tissue?
How are spores/bacteria/virus spread. Wind, water, human, insects?
Does the disease spread by more than one method.
Adaptations to survive and how long it can survive in the soil.

Question 15

What is Hollyhock rust?

Answer 15

Hollyhock rust is a fungal disease.
Affects Alcea rosea (hollyhock), Abutilon, Hibiscus, Malva and Lavatera. (all in mallow family).
Damage/symtoms
Disfigures leaves with numerous yellow/orange spots on surface and raised orange pustules beneath the leaf.
Symptoms start on lower leaves and spread up the plant.
Severely affected leaves shrivel and fall.
Plants are stunted and lacking vigour.
Spread via airborne spores.
Via rainsplash.
Fungus overwinters on the few green leaves remaining at base of hollyhock.

Question 16

How to control and prevent Hollyhock rust?

Answer 16

Cultural control:
Check plants regularly and remove and dispose of affected leaves and heavily infected plants.
Do not collect seed from infected plants
Monitor bought in plants closely for development of symptoms
Hollyhocks will grow for many years, but to reduce the threat from rust grow as biennial discarding after flowering.
Space plants apart sufficiently to reduce high humidity around the foliage.

Chemical control:
Fungus Fighter (contains Tebuconazole as a liquid)
Fungus Clear Ultra (contains Triconazole) as a liquid concentrate or ready to use spray).
Spray twice a week when plants are in rapid growth.

Question 17

What is apple and pear canker?

Answer 17

Apple canker is a fungal disease.
Causes disfiguring and sunken patches of dead bark on the branches of apple and pears and eventually death of the branch. Infections often begin at wounds or buds.
Affects Malus, Pyrus and also Sorbus, Ash and Beech.
Causes round or oval areas of dead, sunken bark and eventually death of brach.
May also infect fruit so they rot on the tree before harvesting or when in store.
Presence of small red/orange or white pustules.
New shoots dying/wilting.
Discoloured leaves.
Infection starts from a wound or bud.
Airborne - spreads by wind, water spash, pruning tools, insects.
Wet soil increases spread.

Question 18

How to control and prevent Apple & Pear Canker?

Answer 18

Canker is reported to be more damaging on wet, heavy and or acid soils, so amend drainage and raise PH by liming if needed.
Completely cut out all affected smaller branches and spurs. With the larger branches try to cut out all infected material.
All such pruning should remove all brown infected bark and wood, cutting back to clean green wood.
Sterilise knife and secateurs with methylated spirits to avoid cross contamination.
Burn prunings.
Pruning back leaves and branches to improve air circulation of older trees to help to stop the disease establishing.
Prevention - prune only in dry weather.
Choose resistant varieties - Apple Crawley Beauty and Pear Concorde.

Question 19

What is Fireblight?

Answer 19

Fireblight is a bacterial disease.
Affects plants in the rose family - apples, pears and related ornamentals including Cotoneaster, Sorbus, Crataegus and Pyracantha.
More of a problem in pears than apples.
In UK it is nearly always too cold at blossom time for infections to occur, so disease is fairly minor.
Trees are at risk when they produce a second small flush of blossom later in the season when conditions are warmer.
Young trees are more susceptible.
Active in late spring until Autumn.

Damage/Symptoms
Blossoms wilt and die at flowering time.
Shoots shrivel and die as infection spreads down inner bark.
In humid/warm weather a glistening white/cream bacterial slime may ooze from affected shoots, branches, fruit.
Cankers on branches especially where infected shoots join larger branches.
Leaves turn dark brown and drop.
Fruits become discoloured and wrinkled.
Severely attacked trees appear to have been scorched by fire.

Question 20

How does Fireblight overwinter and how is Fireblight spread?

Answer 20

Bacteria overwinters in bark cankers.
In warm, wet and windy weather in spring, bacteria oozes out of the cankers.
Infections occur when the bacteria enter the inner bark, usually via the blossoms.
Spread by wind blown rain, pruning tools.
In favourable conditions infection will spread rapidly down the inner bark by 5cm per day.
Plant may die in a few months.

Question 21

How to control/prevent Fireblight?

Answer 21

Cultural control -
Prune out and burn infections promptly.
Peeling back the bark to reveal the brown staining and cutting back 30cm to healthy wood in smaller branches, 60cm in larger branches.
Wipe pruning tools with disinfectant (Melthylated spirits) between cuts to avoid spreading the bacteria.
Remove secondary late blossoms before they open.
Plant resistant cultivars - The ‘Saphyr; range of Pyraantha cultivars are resistant.
No chemical controls of Fireblight.

Question 22

What 3 ways are plant virus’ spread?

Answer 22

Spread by vegetative propagation
Aphid transmission.
And on tools and hands.

Question 23

What ways can you avoid spread of virus’?

Answer 23

Hygiene
Purchase of certified virus free stocks/seeds
Control of aphids.
Avoid growing other susceptible plants in close proximity.
Choose varieties with some resistance.

Question 24

What is Tobacco mosaic virus?

Answer 24

A virus which affects Potatoes, tomatoes and Nicotiana.
Mosaic patterns of lighter green on the leaves. (Leaf mottling).
Fern leaf - were the leaf blade is reduced in size to give a fern like appearance.
Fruit fail to set.
Fruit develop bronzed, patchy appearance.
Poor growth with small fruit.
Necrosis and stunted growth. Leaf curling.

Question 25

When is Tobacco mosaic virus active and how is it spread?

Answer 25

Tobacco mosaic virus is active through the growing season.
Rely on aphids to transmit them from infected to healthy plant.
Spread through contact with hands, tools, seeds.

Question 26

How to control/prevent Tobacco mosaic virus?

Answer 26

Remove plants with symptoms promptly.
After handling infected plants, wash hands and tools in soapy water. Additional precaution sterilise tools with methylated spirits.
Avoid growing other susceptible plants in close proximity.
Grow resistant cultivars - Tomatoes - Cherry wonder and Shirley.
Tobacco mosaic virus occasionally transmitted through seed. Purchase certified virus free seed stock from reputable company.
No smoking/caution with tobacco proximity to plant handling.

Question 27

What is damping off disease?

Answer 27

Damping off is caused by various species (Pythium & Rhizoctonia plus others)
Major problem associated with seed propagation.
Usually sowing seed indoors or under glass in early spring but can occur with direct sowing outdoors.
Affects lettuce, lobelia, antirrhinum, Nicotiana.
Particularly vulnerable if stressed due to poor fertilisation, low light levels, low temperature in early spring.
Seedlings collapse in patches.
White fungal growth on compost.
Seedlings may fail to emerge.
Cuttings rot at the base of the stem.
Can also cause root and crown rot of mature plants.

Question 28

How does ‘damping off’ disease spread?

Answer 28

Both Pythium and rhizoctonia produce resting spores which can survive long periods of time in pots, compost, water on benches.
Once they find themselves in he compost next to a host plant masses of swimming spores are released called zoospores. They need a film of water to move to the host.
Worse when high humidity, poor air circulation, over watered and if seed sown too thick.
Less common now as gardeners use sterilised compost.
This is why garden soil should not be used for germinating seedlings as there are many damping off spores present.
Thought to be spread by sciarid fly.

Question 29

What is the life cycle of Damping Off species?

Answer 29

Damping off species can over winter as hypae on plant debris or as resting spores which can survive long periods of time with no host.
If the environment is moist enough the resting bodies will produce mobile zoospores that swim to the host plant.
These zoospores then encyst and germinate.
If they infect the roots of a seedling, the mycelium will grow throughout the plant tissue

Question 30

How does knowledge of the life cycle and biology of damping off disease contribute to success of control?

Answer 30

Breaking life cycle - removing infection source by using sterile compost, clean trays/[pots with no spores.
Remove infected plant debris to prevent mycelium spread.
Keeping soil just moist - not too damp so that no zoospores develop.
Aim to reduce humidity by not over watering, not sowing too densely and having good ventilation in the greenhouse to stop production of zoospores.
Irrigate seedlings with clean tap water.
Do not overwater.
There is no chemical control!

Question 31

What is Honey fungus? (Armillaria mellea)

Answer 31

The most devastating fungal disease in the UK as they can kill mature trees and shrubs.
There are several species of honey fungus.
Attacks and kills the roots and lower stem of many woody and perennial plants.
Honey fungus lives on dead trees as a saprophyte and can then spread to living trees and shrubs and hedges.

Question 32

Give 4 examples of host plants for honey fungus?

Answer 32

Some plants more susceptible to attack.
Forsythia
Privet
Rhododendron
Betula

Question 33

What are the first symptoms of honey fungus?

Answer 33

When symptoms are detected it is often too late.

Plant has small yellow leaves and stunted growth.
Sometimes first sign is when new leaves do not appear in spring on deciduous trees and shrubs.
Premature leaf fall.
Die back of branches.
Fewer flowers, although plant will often have a flush of flowers prior to death.
Cracking of bark at base of trunk which may be bleeding.
Upper parts of plant die which can be sudden during hot dry weather as a result of the failure of the root system.

Question 34

What other symptoms of honey fungus are there, usually detected on further investigation?

Answer 34

The bark at the base of the shrub/tree can be lifted and underneath is a white sheet of mycelium that smells of mushrooms.
Clumps of honey coloured toadstools sometimes appear briefly on infected stumps in autumn.
Rhizomorphs can be found in the upper 20cm of soil. These are black in colour, and resemble boot laces. They are attached to the roots and lower stem and radiate out from the infected host in search of another host. They can travel 1m a year.
Roots are found to be dead and decaying.

Question 35

Describe the outline of the Honey Fungus life cycle?

Answer 35

Honey fungus spreads through either rhizomorphs or through direct mycelial contact.
In the case of mycelial contact, the roots of an infected host grow near enough to a new host that mycelia simply grow onto the new host and infect.
Rhizomorphs are used if no hosts nearby. It spreads by exploring the soil towards uninfected roots. It can travel 20metres from host!

Question 36

What 3 things do we know in how to reduce the risk of spread of Honey fungus, because of our knowledge of the life cycle?

Answer 36

That it is long lived - so stumps need to be removed.
That it spreads long distances - so do not plant susceptible species within 20-30m.
Rhizomorphs are the main means by which they spread - so create a physical barrier.

Question 37

How can we control and prevent honey fungus?

Answer 37

Some species have good resistance eg. Buxus sempervirens and Acer negundo (Box elder)
Excavate & destroy by burning or waste removal of all the infected root and stump material. This will remove the food source on which the rhizomorphs feed and render them unable to grow in the soil.
Regular deep cultivation will also break up rhizomorphs and limit their spread. This won’t help suffering plant but will minimise the spread.
Do not plant with trees/shrubs for a year.
Remove and replace the infected soil from around the affected plant.
When replanting, select plants with some resistance such as oak, beech, yew, clematis, laurel or mahonia.
Sterilise all tools used on infected material with a household bleach solution.
To prevent honey fungus spreading to unaffected areas, a physical barrier such as 45cm deep vertical strip of butyl rubber (pond lining) buried in the soil will block the rhizomorphs. It should protrude 2-3cm above soil level.
No chemicals are available to treat honey fungus!

Question 38

What is Clubroot and what kind of plants does it affect?

Answer 38

Clubroot is a soil born organism and is not spread by wind.
It causes distorted growth of roots.
It affects plants in the brassica family - brussel sprouts, cabbages, broccoli and ornamental relatives like Wallflowers.

Question 39

What are the damage/symptoms of Clubroot?

Answer 39

Causes roots to become massively swollen and distorted.
Water and nutrient transport systems of infected plants are destroyed.
Severely reduces growth and yield, plants may die.
Stunted growth.
Purplish foliage.
Wilting in hot weather due to poor root system.

Spreads whenever the soil is moist and warm so most new infections occur mid summer until late autumn.

Question 40

What is the lifecycle of Clubroot?

Answer 40

Produces resting spores that can contaminate soil for 5-20 years even without a host plant.
In the presence of a susceptible plant roots, these resting spores germinate and infect the root hairs, causing the distortion.
Swimming spores - zoospores so soil needs to be moist.
They form a jelly like substance not thread like hyphae.
Disease stimulates root hair cells to swell and form galls.
The fungus produces more resting spores in the affected tissue, which eventually rots and releases them back to the soil. Ready for the cycle to start all over again.

Question 41

How does knowledge of the life cycle of Clubroot contribute to the success of control?

Answer 41

Longevity used to determine length of crop rotation.
As resting spores are present in soil, and plant tissue containment of disease means destroying infected plant material and good hygiene so as not to transfer the disease from one plot to another.
Prefers an acid environment, so liming the soils is a good control.
Prefers damp soils - for swimming zoospores. So cultivation and addition of grit sand may help.

Question 42

How to control and prevent clubroot?

Answer 42

Buy guaranteed club root free brassica plants. Don’t accept plats from infected allotments as can be transferred on plant tissue.
If disease present, start plants off in modules to give them a head start.
Beware of spreading the problem on contaminated soil on tools, wheelbarrows or footwear.
Club root reduced (not eradicated) by raising soil PH by liming. Add lime to plant hole.
Remove all plant debris after cropping. Don’t just chop the tops off cabbages.
Improve drainage.
Remove all related weeds like shepherd’s purse and hairy bittercress - host plants.
Select cultivars with a degree of resistance. Eg. Cauliflower ‘Clapton’
Incinerate infected material do not compost.

No chemical treetment.

Question 43

What is potato blight?

Answer 43

Potato blight is the disease that caused the Irish potato famine.
It is a common disease of potatoes and is prevalent in warm wet seasons.
It affects potatoes and tomatoes.

Question 44

What are the symptoms of potato blight?

Answer 44

Brown blotches form on leaves and stem and rapidly spread throughout the plant.
Brown rotting shrivelled leaves.
Affected tubers have a brown decay below the skin surface which spread and the potato rots.
Leaves and stems rapidly blacken and rot causing plant to collapse.
Tomato symptoms the same.

Question 45

How does potato blight spread?

Answer 45

Active in early summer onwards in warm wet weather.
Sporangia (an enclosure in which spores are formed) easily break away from infected foliage and may be wind blown for miles.
Spores need to swim in a water film before settling on the plant surface and penetrating into leaf tissue. This is why the disease is so serious in wet summers.
Also produce resting spores (oospores) in the plant tissues that fall to the soil and contaminate the tubers below ground and remain in the soil.
The pathogen overwinters in potatoes left in the ground or by the side of fields.
Blight less likely to reach glasshouse tomatoes because of protection by glass, but if spores do enter they spread easily due to high humidity.

Question 46

What is the lifecycle of the potato blight disease?

Answer 46

Oospores - resting spores can persist in tubers for a long time. 
Sporangia and zoospores more short lived.
Spores are spread by wind or water. 
The zoospores (swimming spores) released from sporangia have swimming tails allowing further movement in water films on leaves or in soil. Both sporangia and zoospores are short lived, in contrast to oospores which can persist in a viable form for many years.
Sporangia can easily break away from infected foliage and may be wind blown to another plant. If a spore lands on a wet leaf, zoospores are released and dispersed on air currents.

Question 47

How does knowledge of the lifecycle of Potato blight contribute to the success of the control?

Answer 47

Knowledge of it’s favoured conditions allows prediction of outbreaks and good irrigation practice.
Knowledge of the swimming spores helps us to understand how the disease flourishes in wet weather and how it can spready by rain splash.
Knowledge of it’s overwintering sexual spores (oospores) guides the removal of remaining tubers.
Knowledge of asexual and sexual spores production once the tops are infected guides the removal of tops so that spores do not spread to the soil or other plants by wind blown spores as well as removing all plant debris so that no more spores are produced.

Question 48

How to control and prevent Potato blight?

Answer 48

Choose an open planting site with good airflow and leave sufficient space. Better airflow allows foliage to dry quicker after rain.
Crop rotation will help to prevent a build up of disease, and avoid infection being transmitted from volunteer potatoes.
Weed out all volunteer potatoes and try and thoroughly remove all tubers from the soil at the end of the season.
Remove and destroy infected plants, do not compost.
Remove any diseased foliage immediately and do not compost.
Grow resistant varieties - Sarpo potatoes and Tomato ‘Legend’
Earthing up gives some protection.
Early harvested potatoes more likely to escape infection. Grow first earlies.
Buy certified seed potatoes.
Commercial growers have a forecasting system. The ‘Hutton criteria’.

No chemical control available.

Question 49

What is Bacterial Canker? (On Prunus)

Answer 49

A serious disease of Prunus species, especially in cherry and plum orchards. Bacterial diseases need an entrance point to the plant such as a leaf scar, lenticel or wound from pruning. Once inside the disease causes death of the cambium tissue which disrupts the vascular system causing cankers, dieback beyond the canker and holes in leaves.

Question 50

What are the symptoms/characteristics of Bacterial Canker?

Answer 50

Characterised by the death of cambium tissue of woody stems, branches or twigs causing them to sink forming cankers.
Disrupts the vascular system beyond the canker so dieback occurs.
Cankers may exude white slime or amber gum.
Leaves are yellow.
On stems and spurs - sunken, dead areas of bark develop in spring and early summer. Often accompanied by a sticky exudation. (like a gum/resin).
Dark brown spots on leaves i Spring which then fall out causing shot hole appearance.
Smaller branches may become girdled by canker. (circles branch completely.)
Blossom can be brown/wilted.

Question 51

When is Bacterial Canker active?

Answer 51

Bacterial canker is active in Spring, when temperatures start to rise.
Cankers start to form in Spring.
Shot holes on foliage appear from late spring.
Cankers remain more or less dormant through summer when tissues are resistant.

Question 52

How does Bacterial Canker spread?

Answer 52

The bacteria exists as a surface dweller on leaves, and during wet weather in spring or early summer, can enter through the stomata causing infections to develop in more young leaves.
Autumn leaf splash/rain transfers the bacteria to woody tissue of the stems after leaf fall. Enters through abscission scars (where the leaf was attached) or wounds.
(Shouldn’t be any man made wounds if pruned at the correct time).

Question 53

Describe the outline lifecycle of Bacterial Canker?

Answer 53

The bacteria overwinters in the bark tissue at the canker margins, healthy buds, or in the vascular system.
In Spring the bacteria emerge and multiply and are spread by wind and rain to leaves and blossom and to other stems. Canker develop rapidly.
In Summer Cankers remain more or less dormant when tissues are resistant.
In late Autumn, bacteria are carried by wind-blown rain droplets and rain splash from leaves to other trees and on the same tree. If there are easy access points like leaf scars or wounds, infection occurs.

Question 54

How does knowledge of the life cycle and biology of Bacterial canker contribute to the success of control?

Answer 54

Disease is most infectious in late Autumn and early Spring, so do not prune then.
Carry out pruning when plants are most resistant ie. July. Do not prune in Winter/early Spring when pruning of may other trees/species is done.
Bacteria is long lived and transmits easily so burn any plant remains when pruning back diseased stems.
Bacterium is present on healthy leaves of prunus so good hygiene is essential when pruning even when there is no sign of disease.
Bacteria can be present throughout the vascular system so when pruning need to remove the canker and then cut at least 30cm behind the canker back to healthy, green wood.

Question 55

How do you control/prevent Bacterial Canker?

Answer 55

Carry out all pruning i July or August when tissues are most resistant.
Sterilise tools before, after and between pruning cuts.
Cut out all canker pruning back to healthy wood, and paint promptly with a wound pain to protect the wound from re-infection.
Burn or destroy infected material.
The Cherries ‘Merton Glory’ and ‘Merton Premier’ and Plums ‘Marjorie’s Seedling’ all have some resistance.
Make sure propagation material is disease free.
Make sure tree ties/stakes do not cause wounds.
No chemical treatment available.

Question 56

What is a virus?

Answer 56

Viruses are sub microscopic organisms and are very infectious.
Viruses replicate in living host cells.
Occur through the whole system of the plant.
The only disease that can be transmitted in seeds.

Question 57

What is Potato leaf curl virus?

Answer 57

Potato leaf curl virus is one of the most important potato viruses worldwide.
It is transferred by a vector from plant to plant - the peach potato aphid.
When it feeds on an infected plant, and moves onto a healthy plant the virus passes through the aphid’s digestive system and then replicates in the salivary glands ready to be transferred to the next potato plant. The virus can also be passed on if seed potatoes are infected the previous year.

Question 58

What is the damage/symptoms of Potato leaf curl virus?

Answer 58

Primary infection -
Due to infection in current season by aphid transfer of virus.

Symptoms occur in youngest upper leaves. Leaf margins become necrotic, turn brown and purplish and curl slightly inwards towards the centre of the leaf.
Less apparent than secondary infection and can be missed.

Secondary infection - starts from infected potato from previous season.
Produces more severe symptoms. Leaf rolling is more apparent, the lower leaves are affected and the entire leaf can become chlorotic and sometimes takes on a purple tone. Leaves may become papery.
Decreased vigour.
Lower yield.
When harvested tubers do not store well - necrosis of the tuber tissue may not be apparent at harvest and can develop in storage. Usually appears as small brown spots scattered throughout the tissue.

Question 59

How quickly do plants show symptoms of Potato Leaf Curl Virus?

Answer 59

Plants from infected tubers show symptoms within a month after emergence.
Current season infection develops after aphids probe on potato plants.

Question 60

How is the Potato leaf curl virus spread?

Answer 60

Primarily by the Peach Potato aphid.

Question 61

How can you control/prevent the Potato Leaf curl virus?

Answer 61

Chemical control - insecticides to control aphid population.
Physical control - fleece isolation.
Cultural control -
Not planting vulnerable varieties.
Certain potato varieties have a high resistance. Casanova, Saxon, Vivaldi.
Buy certified virus free seed potatoes.
Remove weeds as an alternative host plant.
Deal with aphid infections.
Destroy volunteers and remove all crop residue.

Question 62

What is the outline lifecycle of the Potato leaf curl virus?

Answer 62

Life cycle is simple.
Once inside the cell it replicates and then spreads throughout the plant.
Most prevalent in years when winged aphids are numerous during spring time.
The leaf roll virus is persistent in the aphid which remains infective throughout it’s life, and may be spread over long distances. For the virus to be transmitted to the plant, aphids need to be feeding on them for a few hours.

Question 63

How does knowledge of the life cycle and biology contribute to the success of the control of Potato leaf curl virus?

Answer 63

Knowing transmitted through aphids means that if aphids are controlled the virus is controlled to some degree.
Know transmitted through vegetative propagation so buy in new certified virus free stock each year and remove volunteers and any crop residue.
Crop rotation.

Question 64

What 4 FUNGAL diseases do we need to know in detail?

Answer 64

FUNGAL DISEASES

Damping Off
Honey Fungus
Club Root
Potato Blight

Question 65

What Bacterial disease do we need to know in detail?

Answer 65

BACTERIAL CANKER

Question 66

Which Virus do we need to know in detail?

Answer 66

Potato leaf curl virus