Download Plant Diseases - Pukekohe High School

Plant Diseases
Fungal, bacterial, viral
Fungi grow best in humid, warm, conditions
• Fungi cannot make their own food so live on
dead or living cells
• Fungi reproduce by spores that are spread by
wind, water or plant pests
• Fungal spores germinate on the plant surface
and grow thread-like hyphae which spread into
the cells.
• The plant cells die as the fungal hyphae feed on
cell sap, multiply and reproduce
Common
fungal types
1. Leaf Spot (black spot)- black dead
areas on leaves, stems & fruit
2. Brown leaf spot
3. Powdery mildew – white spots
that join on leaf surface to form a
matt. Pumpkins, grapes, roses etc
4. Early and late blight – black dead areas spreading from
leaves onto stems and fruits
5. Downy mildew – pale areas on upper leaf surface and soft
white growth on lower surface – grapes, onions, cabbage
6. Botrytis (Mould)-
rotting of tissue which goes
grey/brown and furry – soft fruits
7. Sooty mould – black powdery growth on leaves
growing on sugary honey dew from scale and aphids
8. Damping off – seedling stems rot at soil level and fall
over – very young seedlings
9. Silver leaf – wood rots and leaves turn silver on
surface – stone fruit (cherries, plums, peaches) and some
ornamentals
Bacteria infect a wide variety of plants
• Unlike fungi, bacteria are not spread by
wind but are often spread by insects or
infected seeds
• Bacteria symptoms include collapsed
tissue or rotting of plant parts
Viruses have no cure so plants must be removed and
destroyed
Viruses quickly spread through all parts of plants
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they infect by:
Vegetative propagation. If infected plants are
used for cuttings the new plants will also be
infected
Insect pests spread viruses from plant to plant
when they suck sap
On tools and hands
In seeds
In the soil
Disease control - accurate disease identification
is essential for effective control
Two main methods for control of fungi and
bacteria are:• Cutting off infected areas and burning
them
• Using special chemical fungicides sprays
to kill the spores
Preventing diseases in plants
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Plant disease resistant varieties.
Remove and burn any infected plant parts.
Keep tools, containers and hands clean.
Keep plants pruned and spaced to allow good air circulation.
Control temperature, watering and ventilation to keep greenhouse.
humidity low to discourage fungi growth.
Make sure soil is well drained.
Spray regularly to control pests.
Provide suitable shelter from wind.
Keep weeds under control. They create damp refuges for fungal
spores.
Rotate crops to prevent pest and disease build up.
Provide good growing conditions to produce strong, healthy plants.