Pests & diseases Flashcards
Seasonal display pests and their control
- Aphids: dislodge using jet of water, insecticidal soap or fatty acid spray, attract predators such as ladybirds or lacewings
- Slugs and snails (ragged leaves and slimy trails): copper barriers, beer traps, nematodes, remove at night, ferrous phosphate pellets
- Vine weevil larvae (sudden wilting in later summer, stunted growth): nematode, check under pots where adults hide, Acetamiprid
- Grey mould/Botrytis (fuzzy grey-brown mould on decaying plant material): removes infected foliage immediately, do not over water, space plants to promote air circulation and lower humidity
- Powdery mildew (dry powdery bloom on surface of leaves): mulch to retain moisture at roots, destroy fallen infected leaves to prevent spreading, choose resistant varieties, fungicide tebuconazole
Define a plant pest
Any animal that causes unacceptable levels of damage to cultivated plants, making them unsuitable for the purpose for which they were grown.
Pests may affect the aesthetic value or crop yield.
Pests are mainly insects but also includes molluscs and animals such as birds, mice, moles and rabbits
Define a plant disease
Diseases are caused by micro-organisms rather than animals.
Diseases multiply quickly and are infectious, spreading to other plants quickly.
Diseases rely on optimum environmental conditions to proliferate.
Diseases can be classified into 3 main groups: Fungi, Bacteria, Viruses
Describe the three methods of pest and disease control in plants
Biological: Using a natural predator to seek out and destroy the pest either by eating it or laying eggs in it e.g. ladybird eating aphids. Usually only applicable to control of pests rather than diseases.
Physical / Cultural There is a plethora of methods in this category including using physical barriers to prevent the pest reaching the plant, choosing species which are resistant to the pest or disease, correct pruning techniques to prevent disease entry, good hygiene practices to prevent spread, quarantining new plants, good plant husbandry as many diseases occur when a plant is weak and unhealthy. Removal of infected plant parts will slow down the spread of diseases.
Chemical Chemicals can be sprayed onto foliage or as a root drench and either block breathing pores of insects or poison them after they ingest them via plant sap or eating leaves. Chemical control should always be a last resort and part of an integrated pest management plan.
Pests and diseases of bulbous plants
- Slugs and snails eat young foliage
- Basal rot: base of bulb rots if growing medium is too moist
- Tulip fire: discoloration of foliage with bright orange streaking. Remove affected bulbs.
- Stem and bulb nematode/eelworm
- symptoms: swelling bulbs, stunted and distorted growth
- control: buy good quality bulbs, dig out plant material showing signs of damage and dispose in waste (don’t compost), also clear host plants within 1m radius. Leave infected soil bare for at least 3 years
Pest and diseases of trees and woody plants
- Aphids: knock off with jet or water or use insecticidal soap
- powdery mildew: plant in full sun where possible, allow good air ventilation, water regularly during dry periods, fungicides
- blackspot on roses
- coral spot
- canker
- honey fungus
Describe symptoms and control of blackspot on roses
- Caused by a fungus, Diplocarpon rosae, which infects the leaves and greatly reduces plant vigour.
- rapidly enlarging purplish or black patch appears on the upper leaf surface
- Leaf tissues may turn yellow around the spots and the leaf often drops
-
Control:
- Collect and destroy fallen leaves in the autumn, or bury under a layer of mulch.
- Prune out all stem lesions in spring before leaves appear.
- use fungicides e.g. tebuconazole
- Chose resistant varieties
Describe symptoms and control of coral spot on shrubs
- Fungal disease of woody plants causing branches to die back caused by Nectria cinnabarina
- Small coral-pink raised spots (pustules) form after the branch dies.
- Control:
- Prune in dry weather.
- Good hygiene. Do not leave dead wood to moulder and generate spores in damp corners of garden.
- Prune out infections promptly, remove and burn wood bearing bright orange pustules
- If plant attacked repeatedly check for other stress factors
- No chemical control
Describe symptoms and control of canker on trees
- Cankers are a symptom of an injury often formed by open wound (pruning or branch breakages) infected by bacterial or fungal pathogen
- most common is fungal infection and wound caused by nectria galligena, a stem canker
- Canker diseases frequently kill branches or structurally weaken a plant until the infected area breaks
- Symptoms:
- Cankers are usually oval to elongate. typically, they appear as localized, sunken, slightly discolored, brown-to-reddish lesions on the bark of trunks and branches, or as injured areas on smaller twigs.
- Bark often splits between the diseased and the healthy tissue, and sometimes it may ooze sap or moisture.
- Leaves may appear smaller than normal, pale green to yellow or brown, often curled and sparse.
- Control:
- No chemical control
- Cut away infection
Describe the symptoms and control of honey fungus on trees
- fungus Armillaria that attacks and kill the roots of many woody and herbaceous perennial plants. Fungus spreads underground
- Symptoms:
- white fungal growth between the bark and wood, usually at ground level.
- Clumps of honey-coloured mushrooms sometimes appear briefly on infected stumps in autumn.
- Below soil bark tissue may be soft, rotten and smell of mushrooms.
- In severe cases fungus produces black ‘shoelaces’ under the bark
- Upper parts of the plant die, smaller than average leaves, failure to flower, premature autumn colour
- Control:
- Excavate and destroy by burning/landfill infected root and stump plant material
- No chemical control
- Some less affected plants e.g. buxus sempervirens, Callicarpa
Name one pest and one disease of alpines
Pest: slugs and snails. Control: nematodes, pick off at night, ferrous phosphate pellets
Disease: grey mould (botrytis). Control: remove infected plant material, increase spacing between plants to improve air circulation and reduce humidity. Do not over water.
Describe symptoms and control of common lawn pests and diseases
Leatherjackets: crane fly (daddy long legs) larvae. Grubs feed on roots and basal shoots of grass plants. Damage is yellow patches of grass, confirmed by lifting turf to reveal grubs. Control: in July - September with pathogenic nematodes. No pesticide for home gardeners.
Moles: common in fertile soils with high worm population. Control: trapping or sonic mole deterrents (February - June).
Fusarium patch disease: occurs during mild, humid conditions in spring or autumn. Small, orange/brown spots appear, spread rapidly and kill off patches of grass. Diseased grass is often wet and slimy. Accentuate by high nitrogen levels, alkaline soil conditions. Control: reduce moisture to reduce humidity by increasing drainage, spiking. Avoid alkaline conditions. Remove lawn clippings and thatch. Reduction in annual meadow grass. Control in September - November.
Corticum disease (red thread): attacks mainly red fescue (festuca rubra) and perennial rye grass (lolium perenne) in areas of low fertility. bleached patches of grass, often tinged with red ‘needles’ visible under wet conditions. Damage is mainly superficial. Control: adequate fertiliser application, selection of disease resistant cultivars.
Fairy rings: Bands of dark green turf or crops of toadstools caused by soil inhabiting fungi. Control: lift affected turf, including 300mm either side. Remove soil to 300mm depth and replace with fresh soil from elsewhere, reseed/returf, do in spring or autumn.
Symptoms and control of powdery mildew
Symptoms: fungal disease which appears as white dusty spreading coating on the leave. stems and flowers. Plant tissue can become stunted and distorted. Infection can cause infected plant parts to turn purple-brown colour.
Control: removal of infected parts of the plant, effective irrigation to prevent drying at the roots, use of fungicide e.g. tebuconazole.
Symptoms and control of grey mould (Botrytis)
Symptoms: fungal disease which results in fuzzy grey-brown mould which affects all soft plant tissue e.g. leaves and flowers. It can spread rapidly where there is high humidity. The disease causes a slimy rot and death of the plant.
Control: remove infected foliage immediately, do not over water, increase air circulation around the plant to reduce humidity, reduction of overhead irrigation.
