R2103 4.1 Explain why plant diseases need to be controlled

Question 1

What is a plant disease?

Answer 1

Is an impairment of normal function brought about as an infection of tissue by a micro-organism (fungus/bacteria/virus)

Question 2

Damage caused by Grey mould

Botryis cinerea

Answer 2

1. Fluffy, light grey fungal mass that follows infection
2. Lettuce - whole plant rots off base
3. Can lead to mummified flowerheads in many flower crops
4. Small black seed like structures form in infected material
5. Soft brown rot in strawberries and grapes

Question 3

Damage caused by strawberry powdery mildew

Podosphaera aphanis

Answer 3

1. Damage to leaves, fruits and flowers, affecting yield and quality
2. White powdery fungal infection on lower surface of leaves
3. Upward curling of leaf edges that may turn brown
4. Dry, purplish patches on upper leaf surface
5. The mildew can infect strawberry flowers causing a deep pink colouration

Question 4

Damaged caused by damping off

Caused by several soil borne fungi

Answer 4

1. Infect seedling causing them to damp off and decay
2. Seedlings may fail to emerge
3. Seedling collapse, often submerged in white fungal growth

Question 5

Damage caused by Honey fungus

Armillaria

Answer 5

1. Primarily attacks trees and shrubs
2. Confirming symptoms are toadstools
3. Upper parts of the plant die
4. Smaller, paler than average leaves
5. Failure to flower or unusually heavy flowering usually just before death
6. Permature autumn colour
7. Cracking and bleeding of bark at base of stem
8. Dead and decaying roots with sheets of white fungus between bark and wood smelling strongly of mushrooms

Question 6

Damage caused by rose black spot

Caused by fungus Diplocarpon rosae

Answer 6

1. Rapidly enlarging purplish or black patch appears on upper surface. Leaf turns yellow around this spot.
2. Leaf drop
3. Sometimes spots remain small and leaf does not drop
4. Small, black, scabby lesions may appear on stems
5. Badly affected plants can shed all leaves and vigour is reduced

Question 7

Damage caused by potato blight

Answer 7

1. First symptoms are yellowing of foliage
2. Then black
3. White bloom appears on underside of leaves
4. Stems go black, killing the whole plant
5. Tubers have dark surface spots that internally are brown rot
6. May attack tomatoes - symptoms dark brown blisters on fruit

Question 8

Damage caused by Club Root

Caused by organism: Plasmodiophora brassicae

Answer 8

1. Above ground - stunted growth, purplish foliage and wilting in hot weather
2. Below ground - root system becomes massively swollen and distorted with a loss of finer roots
3. Growth and yeild severely reduced and very badly affected plants may die

Question 9

Damage caused by hollyhock rust

fungal disease caused by Puccinia malvacearum

Answer 9

1. Bright yellow or orange spots of leaf upper surface
2. Reddish-orange to brown limpy, spore-producing pustules on the lower surface
3. Disease tends to start on lower leaves and spreads up the plant
4. Severely affected leaves shrivel and fall, and plants are stunted and lacking in vigour
5. Pustules form on stems and calyx

Question 10

Damage caused by apple and pear canker

fungal disease caused by Neonectria galligena

Answer 10

1. Cankers are round or oval areas of dead, sunken bark, often starting at a wound or bud
2. On small branches and fruiting spurs: infection may girdle the stem and kill it in as single season
3. On larger branches: cankers are perennial, affected area covered with dead bark
4. Eventually the branch will dies above the canker
5. Developing fruit will sometimes rot and fall if attacked
6. Poor shoot growth
7. New cankers form in mid-spring
8. More serious on wet, heavy, acid soils
9. This is a fungus
10. Spores are produced in small, creamy pustules during spring or summer. Older cankers produce characteristic raised red pustules in autumn or winter. Both of these will turn slimy in wet weather, releasing the spores which spread the disease

Question 11

Damage caused by fireblight

Disease caused by Erwinia amylovora

Answer 11

1. Affects only those members of Rosaceae - sub family Pomoideae. Does not infect stone fruits. Main targets pear, hawthorn, Cotoneaster
2. Blossoms wilt and dies at flowering time
3. A slimy white liquid may exude from infections in wet weather
4. Shoots shrivel and dies as infection spreads to inner bark
5. Cankers on branches especially where infected shoots join larger branches
6. General appearance of a burnt tree
7. Bacteria overwinter in the cankers and are spread in water droplets and insects in the spring when it is wet can warm

Question 12

Damage caused by bacterial canker on prunus

Bacterial

Answer 12

1. Forms in early spring
2. On stems and spurs -sunken dead areas of bark develop in spring and early summer, often accompanied by a light brown gummy ooze. If infection spreads all round branch it will die rapidly
3. On leaves - small brown spots appear which are often around and fall out later to leave holes ‘shot-hole’ affect

Question 13

Damage caused by potato leaf curl virus

Aphid transmitted - persistent

Answer 13

1. Leaves of plant show an upward rolling caused by an accumulation of starch in the pallisade mesophyll layer
2. Leaves often light green in colour and may turn red on upperside, purple on lower side
3. Can see net necrosis in some varieties of tubers (brown flecking throughout the vascular tissue).
4. Low yields
5. 2 main potato colonising aphids are the peach potato aphid and potato aphid

Question 14

Damage caused by tobacco mosaic virus

Caused by tobacco, spread by insects

Answer 14

1. Can attack a variety of plants but main host plant are tomatoes
2. Can destroy entire crop of tomatoes
3. Newest foliage growth will show yellow mottling
4. Plant leaves will develop blister like lesions and/or become fern like in appearance. Edges of leaves will begin to crinkle.
5. Fruit production stunted and the few fruits produced will be misshapen and blemished
6. Caused by tobacco in any form comes into contact with the plant. By hands or discarded in soil