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– (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» 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

Soybean root rot & stem canker

Celery spot

Ripe spot (Bulls-eye rot)

Control• Control depends on

• Lifecycle• Knowing conditions for its success

• 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

1. Pre-penetration (leaf surface)

2. Penetration

3. Post invasion

4. Release & dispersal

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)

Lifecycles differ

Hexapoda

eggs (resistant)

* larvae

pupa (resistant)

adult

←

←

↓

↓

↓

* does most damage

Arachnida

egg

* larva

nymph

* adult

← control stages

←

←←

↓

↓

↓

Mites life cycle is dependent on temperature; higher the temperature the shorter the lifecycle

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

Diagrammatic section through the arthropod integument

Hypocuticle →

– 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 similarmust 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:

• Insecticides• Molluscicides • Fungicides• Acaricides• Herbicides• Rodenticides• Nematocides