R2103 4.1 – 4.4 Plant Diseases Flashcards
What is meant by plant disease?
An unhealthy condition caused by bacteria, fungi or virus (collectively known as pathogens)
Describe the damage caused by grey mould (fungus) Botrytis and method of spread.
2 methods of minimising the effects (or preventing)
- Grey fuzzy mould on infected parts of plant
- Discoloration and wilting
- Spread by spores, but also through soil and on plant remains
Minimised by…
- Strict hygiene, use clean equipment, dispose of infected material
- Avoiding damage to plants
- Minimising effects by reducing humidity and increasing ventilation; adequate spacing between plants
- No chemical controls available for amateur gardeners
Describe the damage caused by strawberry powdery mildew and method of spread.
2 methods of minimising the effects (or preventing).
- White powdery deposit over leaf surfaces – upper first, then lower
- Leaves become stunted and shrivelled, curl upwards
- Affected fruit stunted and dull in colour
- Airborne spores infect under dry conditions
- Disease survives as mycelium, overwintering on old living green leaves. Once temperatures rise the disease will start again. Or can survive in sexual state on surviving leaf debris. Once temperatures rise, spores are released.
Minimised by…
- Mulching and watering (from below, avoid water on leaves)
- Prompt removal of infected shoots – don’t shake about
- Resistant varieties
- Systemic fungicides such as Fungus Fighter Plus
Describe the damage caused by damping off and method of spread.
2 methods of minimising the effects (or preventing)
- Emerging seedlings collapse
- Some do not emerge
- Submerged in mass of white fungal growth
- Soil-borne asexual spores spread by water; sexual ones infect roots Pythian and Phytophthora
Minimised by…
- Using commercial, sterile growing media; and brand new pots and containers
- Sowing thinly
- Good ventilation
- Mains water
- Crop rotation
- Cleaning up
Outline the life cycle of damping-off fungi
Damp conditions > Pythium and Phytophthora produce asexual spores which are spread in water and cause the infection
Sexual spores (oospores) produced in infected roots and survive several months (of cold, dry soil conditions)
Describe the damage caused by honey fungus and method of spread
2 methods of minimising the effects (or preventing)
- Attacks the roots of woody and perennial plants, can lead to plant death
- First wilting and yellowing. Die back occurs in the upper parts of plants, particularly in hot weather. Plants may have smaller leaves and fail to flower. Some will display early autumn colour, cracking or resin at the base of the trunk.
- A white fungal growth can be seen between the bark and the wood at ground level
- Spreads through rhizomorphs, and spores from fruiting bodies in autumn. In autumn, honey-coloured toadstools may appear. NB the spores produced are not considered the main source of infection.
Minimise by…
- Excavation and destroy and burn all infected material
- Digging a trench and placing an impermeable barrier such as butyl rubber sheets will block rhizomorphs from spreading
- Select resistant plants, eg. trees such as Taxus, Juglans nigra, Quercus, Buxus are more resistant. Susceptible plants include Syringa, Betula, Malus, Viburnum, Rosa, Rhododendron.
- No chemical controls available
Outline the life cycle of honey fungus
Rhizomorphs spread from infected trees conducting nutrients and energy for infection of tough woody shrub and tree roots.
Mycelium then move up the stem below the bark
Sometimes toadstools are produced at base of infected trunk
Describe the damage caused by rose black spot and method of spread.
2 methods of minimising the effects (or preventing)
- Rapidly enlarging black patch appears on surface of the leaf
- Leaves turn yellow around spots and then drop off
- Sometimes leaves stay with lots of small black spots
- Small, black scabby lesions may appear on young stems
- Spread – in water to initiate new infections. Likes warm wet conditions
Minimise by…
Collecting and destroying fallen leaves or burying under thick mulch
Prune out all lesions in spring
No resistant varieties, shrub roses most resistant
Fungicide containing Myclobutanil
Name a systemic fungicide ingredient
Myclobutanil
Describe the damage caused by potato blight and method of spread.
2 methods of minimising the effects (or preventing)
- Wilting, yellowing of foliage then turn black with Wichita bloom on underside of leaves
- Stems may blacken and whole plant die
- Tubers have dark surface spots
- Spread by sporangia blown on wind and land on leaves or stems
Minimised by…
Buying seed potatoes from reputable source and resistant variety – Sarpo Axona Rotation of crops
Don’t leave any potatoes in the soil
Burn all diseased material
Outline the lifecycle of potato blight fungus
Sporangia are released from infected leaves - blown on wind and then they need water to settle and penetrate into Leaf tissue. Sporangia also infect tubers and infected tubers grow new shoots containing sporangia. Don’t leave any tubers in The ground over winter - destroy Crop rotation at least every 4 years Earthing up Burn all infected material
Describe the damage caused by clubroot and method of spread.
2 methods of minimising the effects (or preventing)
- Brassicas stunted and wilted foliage and have purple tint
- Roots swollen and distorted
- Growth and yield severely reduced.
Minimised by…
- Lifting and burning diseased plants
- Raising soil pH by liming
- Buying plants from certified grower
Outline the lifecycle of clubroot
Resting spores in the ground for up to 20 years. They germinate and infect root hairs causing distortion Produces more spores in affected tissue which rots and releases them back into soil. Brassicas mid summer to late autumn moist warm soil.
Describe the damage caused by hollyhock rust and method of spread.
2 methods of minimising the effects (or preventing)
- Bright yellow and orange spots on upper leaf
- Reddish brown lumpy spores on underside of leaf
- Starts on lower leaves and works upwards; pustules on stem, stunted growth reduced vigour
- Spread by airborne spores
Minimise by…
- Checking and removing infected plants
- Monitoring bought in plants
- Growing as biennial
- Avoiding dense planting
Describe the damage caused by apple and pear canker and method of spread.
2 methods of minimising the effects (or preventing)
- Round areas of dead sunken bark usually at a bud or wound
- Cambium layer killed
- Eventual death of branch
- Developing fruit sometimes attacked which rot and fall
- Fungus spores spread on wind in spring and enter through damaged parts of plant
Minimised by…
- Cutting canker out or removing branch and burning
- Improving drainage and raising pH by liming
