Diseases Flashcards
What is a plant disease?
An unhealthy condition in a plant, caused by a virus, bacteria or fungi.
Why do plant diseases need to be controlled?
Plant diseases cause damage to plants, even mature plants, and will reduce yield and spread to other plants if left untreated.
Describe the damage done by Grey Mould, the method of spread and two methods of control or prevention.
DAMAGE: Visible grey fluffy fungus growing on stems, leaves, buds, flowers and fruit.
Leads to soft fruit rot (eg Strawberries), and die back of affected parts of plant, and eventually whole plant.
SPREAD: Fungus. Entry of spores to pruning wounds or leaf scars. Sclerotia from infected plants can overwinter in dead plant material, re-infecting in the spring.
CONTROL: Preventing right conditions crucial. Avoid overwatering, improve air circulation to reduce humidity (Cultural)
Remove and destroy infected material (physical).
Describe the damage done by Strawberry Powdery Mildew, the method of spread and two methods of control or prevention.
DAMAGE: White powdery fungal coating on leaves, leaves curl and brown. Results in reduced growth (photosynthesis reduced) and yield (distorted fruit).
SPREAD: Fungus. Entry of airborne spores on (usually upper) leaf surface. Overwinters on dead plant material or within plants.
CONTROL: Preventing plants getting too dry and stressed with regular watering (cultural).
Mulch around plants in summer to prevent soil surface evaporation (physical).
Myclobutanil foliar application (chemical).
Describe the damage done by Damping Off, the method of spread and two methods of control or prevention.
DAMAGE: Seedlings wilt or collapse as root and stems rot, and/or seedlings show fuzzy white fungal growth. Results in death of seedlings.
SPREAD: Soil borne fungal disease, spores enter via roots, and are carried in soil water.
CONTROL: Prevention by using sterile growing medium, cleaning trays/pots and equipment before use. Use tap water on seedlings to prevent contamination from rainwater collection tanks, ensure seeds are grown with the correct spacing - more likely to happen in overcrowded conditions (cultural).
Cover water tanks to stop rotting plant material contaminating water storage tanks (physical).
Describe the damage done by Honey Fungus, the method of spread and two methods of control or prevention.
DAMAGE: Tree/shrub foliage wilts and dies back in spring, lower trunk becomes soft and rots, with white fungal growth developing under bark. Honey coloured toadstools may at base of affected plants in Autumn. Results in eventual death of tree/shrub.
SPREAD: Fungal. Roots are attacked by “bootlaces”, eg long black rhizomorphs spread out from infected plants and infect other susceptible plants from underground.
CONTROL: Prevention by not planting new trees and shrubs too deep, which weakens the plant. Plant trees and shrubs that are resistant if problems are apparent, eg Ilex aquifolium, Taxus baccata.
Remove as much of the infected stump as possible do not leave in ground to infect other plants. If stump cannot be removed, dig a pit around it to 70cm depth and install butyl lining as a physical barrier to the spread of the rhizomorphs (physical).
Describe the damage done by Rose Black Spot, the method of spread and two methods of control or prevention.
DAMAGE: Dark spots appear on leaves of roses, surrounding leaf yellows and drops off. Weakens entire rose plant and reduces vigour.
SPREAD: Fungal spores enter the leaves via water droplets. Fallen infected leaves harbour spores.
CONTROL: Prevention by trying avoid wetting foliage when watering, regular removal of dropped leaves and disposing of responsibly to prevent reinfection (cultural).
Myclobutanil can be applied regularly as a foliar spray (chemical).
Describe the damage done by Potato Blight, the method of spread and two methods of control or prevention.
DAMAGE: Leaves turn yellow, then turn black with a white bloom underneath, stems go black and plant dies. Potato tubers damaged with dark spots, and rot.
SPREAD: Fungal spores enter leaves or stems, spread by rainsplash, or infected tubers are left in the ground over winter, and produce spores which infect other plants.
CONTROL: Prevention by only using certified disease free seed potatoes, and by planting first early cropping varieties which develop tubers prior to the blight taking hold, or resistant varieties, such as ‘Valor’ (cultural).
Remove and burn infected material (physical)
Describe the damage done by Clubroot, the method of spread and two methods of control or prevention.
DAMAGE: Plant wilts, leaves turn purple or develop chlorosis, growth is stunted and yield is reduced. Source of damage is swelling of roots (hence the name), which restricts air, water and nutrient uptake and may also start to rot. Affects brassicas.
SPREAD: Fungus. Moves via zoospores in soil water, which infect root hairs first, then eventually the whole root system. Resting spores can live in the soil for up to 20 years.
CONTROL: Prevention by strict crop rotation cycle, and avoid using Brassica green manures. Grow resistant varieties such as Savoy cabbage ‘Cordesa’ F1, or Brussels Sprouts ‘Crispus’ (Cultural). If soil is acidic, try to raise pH by liming the soil if possible, or use pots/raised beds or grow other crops if the ground is not suitable.
Weed regularly and do not allow brassica weeds to develop, eg Capsella bursa pastoris. Remove any infected plants and destroy, dont compost (Physical).
Describe the damage done by Hollyhock Rust, the method of spread and two methods of control or prevention.
DAMAGE: Raised grey (turning red/orange) spots on underside of leaf, followed by corresponding orange/yellow spots on upper side of leaf. Lower leaves affected first. Leaves then shrivel and drop off. Stunts growth and makes for an unattractive plant.
SPREAD: Fungal spores in soil infect shoots of new plants as they grow. Two kinds of spores produced, one carried by the wind (released in summer, do not survive winter, one by water droplets (released late summer, do survive winter). Like majority of fungal diseases (not powdery mildew), require damp conditions to flourish.
CONTROL: Hard to prevent once present, so treat hollyhocks like biennials, although they are perennials, and remove infected plants and destroy (Physical). Avoid saving seed from infected plants, as they are likely to also be infected (Cultural).
Fungicides like Myclobutanil can be used to treat plants during the growing season to hold back the effects until after flowering, but not a long term solution (Chemical).
Describe the damage done by Apple and Pear Canker, the method of spread and two methods of control or prevention.
DAMAGE: Branches have lesions or dark patches on bark, which worsens into cankers (sunken patches). Foliage above large cankers (girdling stems) dies back.
SPREAD: Spores enter through lenticels, leaf scars and pruning wounds in Autumn/Winter. Rain splash transfers spores to other parts of the tree and remains in infected wood.
CONTROL: Ensure tools are kept clean and sharp to limit wounding. Dont prune in damp conditions. Check trees regularly for symptoms. Ensure plant has enough water and nutrients through good soil care so plant is strong and not stressed. Raise soil pH to neutral by liming as more likely to occur in acidic soil conditions (Cultural).
Prune out infected material and dispose of carefully (Physical).
Describe the damage done by Bacterial Canker, the method of spread and two methods of control or prevention.
DAMAGE: Stems and branches develop swollen areas, which crack and ooze amber gum. Infected leaves get dark spots then holes. Fruit will also ooze gum if infected. Affected branches and stems die back.
SPREAD: Bacteria enters through pruning wounds, leaf scars, and through shoots and flowers. Insects visiting different sections of the plants can spread the bacteria around, also spread by water droplets. Humid conditions aid spread. Affects Prunus species.
CONTROL: Ensure tools are kept clean and sharp to limit wounding. Dont prune in damp conditions. Check trees regularly for symptoms. Choose resistant varieties eg Plum ‘Marjorie’s Seedling’ or Cherry ‘Merpet’ (Cultural).
Prune out affected areas as soon as noticed, and treat pruning site with wound paint (physical).
Describe the damage done by Fireblight, the method of spread and two methods of control or prevention.
DAMAGE: Affected branches see blossoms wilt, foliage turn brown and die back, stems may have slime or brown stains. Affects Rose family (incl apples etc). When infection reaches trunk, whole plant can die.
SPREAD: Bacteria infects through stomata, lenticels and flowers. Insects and rain splash transfers bacteria. Humid, warm conditions required (not a winter disease).
CONTROL: Check plants regularly for signs of disease - fast action necessary as spread by pollinators. Ensure tools and equipment (eg gloves) are clean and sharp to prevent transfer and limit wounding (Cultural).
Prune out any infected material all the way back to the main stem. Treat pruning site with wound paint to seal.
Describe the damage done by Potato Leaf Curl Virus, the method of spread and two methods of control or prevention.
DAMAGE: Leaves roll upwards, chlorosis, stunted plant growth. No damage to tubers, but yield seriously reduced, with fewer, smaller tubers.
SPREAD: Spread via aphids (eg Peach Potato Aphid), or by infected tubers which will mean next years crop will be infected even if no aphids present.
CONTROL: Select a resistant cultivar such as ‘Valor’. Dont keep tubers for next year, buy certified disease free seed potatoes from a reputable source. (Cultural)
Remove infected plants and burn or bin them. (Physical).
Control aphids present on nearby plants, by encouraging aphid predators (Cultural/Biological) or by using insecticides (eg fatty acids, plant oil or Pirethrin/Deltamethrin based sprays) if necessary (Chemical).
Describe the damage done by Tobacco Mosaic Virus, the method of spread and two methods of control of prevention.
DAMAGE: Mottled discolouration of leaves, especially in a ‘mosaic’ pattern between leaf veins. Leaves die back. Discoloured, inedible fruit (in tomatoes), reduced yield and eventual death of plant.
SPREAD: Can be spread through small wounds such as side shoot pinching off, transferred by contact eg hands or tools, or by aphids feeding on plants. Can overwinter in seeds from infected plants.
CONTROL: Maintain hygienic practices (clean tools and hands/gloves). Do not collect seed from infected plants, use certified disease free seed. Choose resistant cultivars if possible eg ‘Nimbus’ (Cultural).
Remove and burn/bin (do not compost) infected material. (Physical)
Control aphids present on nearby plants, by encouraging aphid predators (Cultural/Biological) or by using insecticides (eg fatty acids, plant oil or Pirethrin/Deltamethrin based sprays) if necessary (Chemical).
