Soft growth
Rapid, nitrogen-rich vegetative growth can provide highly suitable feeding tissue for sap-feeding pests.
Encouraging beneficials
Environment
Biological control does not happen separately from the crop environment. Temperature, humidity, light, plant growth and habitat all influence whether pests or beneficials gain the advantage.
Environment is part of pest control
Pest pressure is not determined by the pest alone. The crop and its environment decide how quickly pests reproduce, how stressed the plant becomes and how effectively predators and parasitoids can respond.
This means environmental management can be an important part of IPM. Sometimes a small change in crop conditions can shift the balance without directly treating the pest at all.
Environment
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Plant
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Pest
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Beneficials
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Management
Temperature — speed matters
Temperature influences metabolism, development, reproduction and activity. Both pests and beneficials respond to warmth, but they do not necessarily respond at the same speed.
Pest response
- Aphids, thrips and spider mites can reproduce rapidly in favourable temperatures
- Short generation times allow populations to exploit warm periods quickly
- Heat and water stress can make crops more vulnerable to some pests
- Sudden warm periods can produce rapid increases in pest pressure
Beneficial response
- Predators and parasitoids also become more active as temperatures rise
- Each beneficial species has its own useful temperature range
- Establishment and reproduction still take time
- Extreme or rapidly changing conditions can reduce performance
The important question is not simply whether conditions are warm, but whether they favour pest growth faster than beneficial response.
Humidity — often overlooked
Relative humidity influences water loss, egg survival, activity and establishment. It can be especially important for very small arthropods such as predatory mites.
Hot and dry conditions
- Can favour spider mite population growth
- Can increase plant water stress
- May reduce establishment of some predatory mites
- Can contribute to rapid pest increases during warm weather
More favourable humidity
- Can improve survival of some predatory mite eggs and juveniles
- Reduces excessive desiccation stress
- Can support more stable biological populations
- Needs to be balanced against crop disease risk
More humidity is not automatically better. The aim is a crop environment that supports beneficial activity without creating unacceptable disease risk.
Light — mostly through the plant
Light affects insects partly through activity and behaviour, but one of its biggest effects is through the crop itself.
Increasing light drives photosynthesis and growth. When water and nutrition are well balanced this can produce a strong crop. When they are not, rapid soft growth or plant stress can create opportunities for pests.
- Increasing spring light drives new crop growth
- Young tissue can become attractive to aphids and thrips
- Longer days increase activity of many insects
- Artificial lighting can extend biological activity in protected crops
- Crop nutrition and irrigation need to keep pace with increasing light
Plant growth — the link between climate and pests
Pest pressure often reflects the condition of the plant as much as the number of insects entering the crop.
Water stress
Water stress changes plant physiology and canopy conditions and can contribute to environments in which mites and other pests become difficult.
Dense canopies
Canopies create their own microclimates. Temperature and humidity around a leaf can differ considerably from measurements taken elsewhere.
Balanced growth
Stable irrigation, nutrition and crop growth make pest pressure easier to interpret and biological programmes easier to manage.
Plants provide more than flowers
Flowering plants provide nectar and pollen, but vegetation also changes the physical environment around beneficial insects.
- Nectar can provide energy for adult parasitoids and predators
- Pollen can provide an alternative food source for some beneficials
- Plant structure provides shelter and hunting surfaces
- Canopies buffer temperature, wind and humidity
- Continuous vegetation provides somewhere to persist between pest outbreaks
This is why habitat planting works best as part of the crop system rather than simply as decoration around it.
Habitat structure — where beneficials persist
Crop systems that are repeatedly cleared, sprayed or disturbed provide fewer places for beneficial populations to survive between pest outbreaks.
- Edges and margins can act as refuges
- Hedges and perennial vegetation provide long-term structure
- Ground cover and organic matter can support soil predators
- Flowering strips provide food and movement corridors
- Undisturbed areas can help recolonisation after crop operations
A completely tidy system is not always a biologically resilient system.
Read the environment alongside scouting
Pest counts become more useful when they are interpreted alongside the conditions driving them.
Temperature rising?
Expect development and reproduction rates to change.
Hot and dry?
Watch particularly closely for mite and thrips pressure.
Rapid soft growth?
Increase attention to aphids and other sap feeders.
Beneficials present?
Ask whether conditions are helping them establish and reproduce.
Everything is linked
- Environment shapes crop growth
- Crop growth influences pest opportunity
- Pest populations provide prey and hosts for beneficials
- Beneficials suppress pest population growth
- Management can strengthen or disrupt every stage of the system
Good IPM is not only about choosing what to release or spray. It is also about managing the conditions in which the biology operates.
Next: Seasonality
The environment is constantly changing through the season. Spring, summer and autumn create different pest risks and different opportunities for beneficial insects.
Explore seasonality →