3.Pathogens

Question 1

What is meant by plant disease?

Answer 1

An unhealthy condition or damage caused to a plant by bacteria, fungi or virus (collectively known as pathogens)

Question 2

Damage caused by Grey mould (Botrytis) and method of spread

Fungi

Answer 2

• Very common fungus, affects almost all living or dead plant matter
• Grey/white fuzzy mould on infected parts of plant
• Discoloration and wilting, infected areas shrivel and rot
• Enter plant through wounds (bud scars/pruning wound)
• Spores spread through wind, but also through soil and on plant remains
• It needs humidity to become active

Question 3

Control of Grey mould (Botrytis)

Fungi

Answer 3

• Strict hygiene, use clean equipment
• Cut back infected material and properly dispose
• Reduce humidity; adequate spacing between plants
• Increasing ventilation; prune to allow air flow
• No chemical controls are completely effective

Question 4

Damage caused by Damping off and method of spread

Fungi

Answer 4

• Seedlings are usually affected at soil surface
• Emerging seedlings collapse in a mass of white fungal growth
• Most occur naturally in soil and spores spread by water

Question 5

Control of Damping off

Fungi

Answer 5

• Use commercial, sterile growing media
• Brand new/ clean pots and containers
• Sowing thinly
• Do not overwater
• Good ventilation
• Crop rotation
• No chemical control

Question 6

Damage caused by Honey Fungus and methods of spread

Fungi

Answer 6

• Attack and kill roots of woody and perennial plants
• White fungal growth between bark and wood
• Upper plants of plants die - indicating failure of root system
• Cracking and bleeding of bark at base of stem
• Spreads underground by rhizomorphs through infected roots in the soil
• Can attack plants up to 30m away from source of infection

Question 7

Control of Honey Fungus

Fungi

Answer 7

• Excavation and destroy, 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. Quercus, Buxus
• No chemical controls available

Question 8

Damage caused by Potato blight and method of spread

Fungi

Answer 8

• Causes rotting of tubers and fruit on potato/tomato plants
• 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
• Spores spread through wind/ water and land on leaves or stems
• Infected spores need water to be able to penetrate leaves
• Overwinters in rotten potatoes

Question 9

Control of Potato blight

Fungi

Answer 9

• Using resistant variety – Sarpo range (potato) Legend range (tomato)
• Rotation of crops - min 4yr
• Grow tomatoes in glass house to prevent spores from reaching fruit
• Don’t leave any potatoes in the soil
• Check warnings - smith
• Burn all diseased material, never compost
• No chemical control

Question 10

Damage caused by Clubroot and method of spread.

Fungi

Answer 10

• Causes damage to Brassicase - cabbage, cauliflower, brussel sprouts
• Chlorosis - pale/pinkish leaves
• Wilt rapidly
• Plants fail completely/reduced crop
• Stunted growth

Question 11

Control of Clubroot

Fungi

Answer 11

• Lifting and burning diseased plants
• Improve soil drainage
• Select resistant cultivars
• Raising soil pH by liming
• Crop rotation
• No Chemical control available

Question 12

Outline the lifecycle of Clubroot

Fungi

Answer 12

• Resting spores in the ground for up to 20 years.
• They germinate and infect root hairs causing distortion
• Produces jelly like mass within plant root
• Uptake of food and water is effected
• When roots degrade more spores are released into soil

Question 13

Control of Apple and pear canker

Fungi

Answer 13

• Cutting canker out or removing branch (treat exposed wood to prevent further infection)
• Avoid pruning during damp weather
• Improving drainage
• Raising pH by liming
• No chemical control available

Question 14

Damage caused by Apple and pear canker and method of spread

Fungi

Answer 14

• Round areas of dead sunken bark usually at a bud or wound
• Cambium layer killed
• Branch may become swollen, foliage and growth above dies
• Developing fruit sometimes attacked which rot and fall
• Fungus spores spread through rain splash and enter through damaged parts of plant

Question 15

Damage caused by Strawberry powdery mildew and method of spread

Fungi

Answer 15

• Purple, yellow, red spots on leaves
• Fluffy white deposit over leaf surfaces – upper first, then lower
• Leaves become stunted and shrivelled, curl upwards
• Affected fruit stunted/ distorted and dull in colour
• Airborne spores infect strawberries and Hops
• Once temperatures rise, spores are released

Question 16

Control of Strawberry powdery mildew

Fungi

Answer 16

• Mulching and watering (from below, avoid water on leaves)
• Prompt removal of infected shoots – don’t shake about
• Water soil through at the base - shouldn’t let soil dry out
• Resistant varieties - Pegasus
• Potassium bicarbonate provides resistance

Question 17

What is a bacterial disease?

Answer 17

• Bacteria are minute organisms, they can beneficial or detrimental
• More common in hotter/tropical climates
• They can cause serious problems to plant health

Question 18

Symptoms and spread of Bacterial canker of Prunus?

Bacterial

Answer 18

• Affects ‘Prunus’ genus - e.g Plum, peach, cherry, apricot
• Swollen areas on stems/cracking can occur
• Amber like resin
• Small, yellow leaves with brown spots
• Wind blown rain droplets enters through wounds/scars

Question 19

Control of Bacterial canker of Prunus?

Bacterial

Answer 19

• Use resistant root stocks/cultivars (e.g Warwickshire drooper)
• Prune affected areas in summer months
• Burn or properly dispose of infected material
• No chemical control is available

Question 20

Symptoms and spread of Fireblight?

Bacterial

Answer 20

• Causes damage to the ‘Roseatie’ family
• Flowers wither/die back followed by surrounding leaves and stems
• If bacteria reaches the trunk it may cause death within 6weeks - trunk looks like a burnt tree
• Bacterial slime can be seen in hot weather
• Can be spread by bee’s as they pollinate
• Can be spread by harmful insects such as Aphids
• Can be spread by rain

Question 21

Control of Fireblight?

Bacterial

Answer 21

• Carefully prune to 60cm below infected/stained wood
• Burn all infected material
• Sterilise all equipment

Question 22

What is a viral disease?

Answer 22

• Viruses are much smaller than bacteria, the particles take over the cell nucleus to produce more virus particles
• They are very hard to control with chemicals as the virus can penetrate the plant so deeply than any chemical would need to do the same

Question 23

Symptoms and spread of Leaf curl potato virus?

Viral

Answer 23

• Leaves become thickened/roll due to a build up of starch
• Serious reduction in yield
• Leaves can turn red/purple
• Carried by Peach potato aphid which can be blown a considerable distance by the wind

Question 24

Control of Leaf curl potato virus?

Viral

Answer 24

• Do not use last years crop as seed potato (especially if infected)
• Use cultivars such as ‘Valor’
• Remove any plants showing symptoms
• Use insecticides as a preventative measure

Question 25

Symptoms and spread of **Tobacco mosaic virus**? ## Footnote **Viral**

Answer 25

* **Distorted** small leaves * **Yellow mottling/ mosaic** pattern on leaf * **Brown streaky stem** can sometimes be seen in summer * **Fruit yield** can be affected e.g ripe fruit is hard an inedible * Enters plant through **micro wounds** * Can be easily spread by **gardeners hands** * Virus can be passed on **through seed**

Question 26

Control of **Tobacco mosaic virus**? ## Footnote **Viral**

Answer 26

* **Heat treatment** of dry seed to kill of virus * Use **Nutrient film technique** to prevent use of infected soil * Use resistant **cultivars** e.g Cherry wonder

Question 27

What is meant by **Fungicide?** ## Footnote **Considerations?**

Answer 27

Used to prevent/cure **diseases caused by fungi** Different modes of action: * **Preventative/protective** - coats foliage and prevents disease from entering (must be thoroughly covered) * **Systemic** - chemical is absorbed and works on the disease within the plant **Considerations** * **Lower** levels of **toxicity** however care must be taken when mixing * **Ensure** plants have optimal growing conditions, good soil fertility and the right micro climate to reduce the chance of fungal infections * **Avoid** introduction of affected plants * Ensure fungicide is **compatible** with biological control methods and does not harm beneficial insects before use