Transcript L1 Pesticides

L1 Pest control
Anna Drew
Pest control
• Whether or not a pest depends on numbers
present
– Fungi
– Insects
– Virus
• viral infected plant material has to be burnt
– great loss of money
– not as common
Fungi (Eumycetes)
• Hard to control
• Mutate easily compared to insects
• ‘Thallophyte’ members
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(not differentiated into root, stem and leaves)
Either parasitic – living on living animal/plant
Or saprophytic – living on dead or decaying organic matter
Devoid of chlorophyll
Plant body made of filaments or hyphae = mycelium
– Characterised by
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Spore production
Spore character
Type mycelium
Type of colony produced
↓ importance of
characters gradually
reduced
Examples
• Phycomycetes
• Eg Phytophora infestans – potato blight
• Ascomycetes
• Eg Venturia inaquelis – apple scab
• Basidomycetes
• Eg Puccinia sp. – rusts (cereals)
• Visual effects give common names
Type of disease
• Depends what it affects:
• Root
» wilt, damp (rot)
» eg Fusarium sp -> soybean
• Leaves
» smut or spot
» eg Septoria sp -> celery
• Stems
» cankers -> soybean
» [eg Rectria galligens]
• Fruits
» scabs or rot diseases
» eg Gleosporium perennans -> apple
Celery spot
Soybean root rot
& stem canker
Ripe spot
(Bullseye rot)
Control
• Control depends on
• Lifecycle
• Knowing conditions for its success
1. Pre-penetration (leaf surface)
4. Release & dispersal
2. Penetration
3. Post invasion
• May need more than one host
• 1+2 depend on climatic conditions
» ie avoid humidity by pruning to open it out a bit
• 3+4 depend on susceptibility of plant
» eg fungi and resistance
Insects
• Arthropoda (segmented body, jointed limbs)
– Arachnida (mites)
• 8 legs
• 2 segments (head and thorax fused)
• (no wings)
– Hexapoda (insects proper)
• 6 legs
• 3 segments (head, thorax, abdomen)
* does most damage
Lifecycles differ
← control stages
Hexapoda
Arachnida
eggs
egg
(resistant)
↓
* larvae
↓
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↓
pupa
←
↓
(resistant)
nymph
←
↓
↓
adult
* larva
←
Mites life cycle is dependent on temperature;
higher the temperature the shorter the lifecycle
* adult
←
Points of control
• Also the reasons they are hard to control (areas
to hit):
– Exoskeleton = contact poisons
• absorbed through the body wall
• must come into direct contact with the insect to kill
– Alimentary canal = stomach poisons
• ingested and kill by action on
• or absorption into digestive system
– Respiratory system = fumigents
• Enter tracheal system in the form of a gas
Exoskeleton
Hypocuticle →
Diagrammatic section through the arthropod integument
– Epicuticle
• = cement, wax or polyphenol
• aids in reducing evaporative water loss
– Exocuticle + endocuticle = procuticle
– Exocuticle
• = chitin – polymerised amino sugar and phenol
• makes it hard and impermeable
• Larval stage: cuticle very soft
• Nymphoidal stage: may be shedding, vulnerable
• Adult stage: good protection but segmented for
articulation and chemicals can be absorbed
• Alimentary canal
– Main absorption is in the midgut
– Rest of the canal is covered with chitin lining
• Respiratory system
– Simple system of internal trachea
– Air enters on either side by spiracles
– Take up the fumigant (unless it causes
spiracles to close)
– Not good for humans (in confined spaces)
• Nervous system
– Paired ganglia to each segment
– Connected to head
– Main way drugs eventually act
Methods of control
• Fungi
1. Natural control -> plant breeding to produce resistant
- fungi can change more quickly
2. Biochemical control – all ↑ plant resistance
- may cause thicker cuticle production
- or change in metabolism eg ↑ sugar levels
- or keep stomata closed
3. Chemical control
(a) contact on the surface
aimed at the spore or in wax layer
(b) systemic take up via root/leaves and transport in plant
problem is biochemistry of plant/fungi similar
must be non-phytotoxic
• Contact always before infestation, systemic not always necessary
• Insects
– Natural control
• Inside greenhouses control climate
• Outside change habitat eg drainage
– Legal control
• On moving live plant material between countries
– Biological control
• Investigate natural predators that can be introduced
• Contact method – kill all so natural predator has nothing to
eat or a lower stage in the food chain runs life
– Chemical control
• Contact – collects on exoskeleton
• Systemic – useful for aphids that suck sap
Plant cuticle
– Important in formulation for contact pesticides
• will it run off or cover whole plant?
• governed by water repellancy
– 2 factors:
• surface roughess
– depressed stomata
• composition of wax
– straight chains of alkane, hydroxy alcohols + keto acids
– will alter water repellancy
Pesticide classification
• According to type organism against which
they are effective:
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Insecticides
Molluscicides
Fungicides
Acaricides
Herbicides
Rodenticides
Nematocides