Insect Nets creates a physical barrier around ventilation openings. It allows air to move through the greenhouse while reducing the entry of pests such as whiteflies, thrips, aphids and some other flying insects.
For Kenyan farmers, pest exclusion is particularly useful because insects can spread quickly in warm greenhouse conditions. Once pests enter the structure, controlling them can become more difficult and expensive.
The Importance of Pest Exclusion Netting
Unlike chemical pesticides, which are normally used after pests have already entered, insect nets provide a physical barrier. They are usually installed over side vents, roof vents, doors and other openings where insects could enter.
The effectiveness depends heavily on mesh size. A net with large openings may allow smaller insects to pass through, while an extremely fine net can restrict airflow. This creates an important balance between pest exclusion and ventilation.
A properly designed insect exclusion system can help reduce the number of pests entering the greenhouse. It does not guarantee that insects will never be present because pests can enter through doors, clothing, planting materials, tools or other routes.
Why Whiteflies Are a Problem
Whiteflies are small flying insects that commonly attack crops grown under protected conditions. Whiteflies are known to reproduce quickly under favourable conditions. This means a small population can become a serious problem if it is not detected early. Their causes;
- Feeding on plant sap.
- Weakening plants.
- Causing yellowing and poor plant growth.
- Producing honeydew on leaves.
- Encouraging the development of sooty mould.
- Spreading certain plant viruses.
Other Pests Excluded by Insect Nets
Good-quality insect netting can also help reduce entry of:
- Thrips.
- Aphids.
- Leafminers.
- Some moths.
- Some beetles.
- Other flying insects.
Insect Netting and Greenhouse Polythene Sheet
The greenhouse polythene sheet is the main weather covering. It protects the greenhouse from rain and provides a controlled environment while allowing sunlight to enter.
Insect netting is mainly used at ventilation openings and pest exclusion.
Using the materials together can create a more complete protected farming system.
| Material | Main Function |
| Greenhouse polythene sheet | Weather and environmental protection |
| Insect netting | Pest exclusion |
| Shade net | Reduces solar radiation |
| Ground cover | Weed and soil management |
| Bird netting | Bird exclusion |
Mesh Counts: 40 Mesh vs 50 Mesh Specifications
Mesh count describes the number of openings in a given measurement of the net. In general terms, a higher mesh count means smaller openings.
40 Mesh
A 40-mesh net provides a relatively fine physical barrier while allowing good airflow. It can be suitable for general insect exclusion where the main objective is to reduce the entry of larger flying pests.
50 Mesh
A 50-mesh net has finer openings and provides stronger exclusion of smaller insects. However, because the openings are smaller, airflow resistance can be greater.
This is an important consideration in hot areas of Kenya.
| Specification | 40 Mesh | 50 Mesh |
| Mesh density | Fine | Finer |
| Opening size | Generally larger | Generally smaller |
| Pest exclusion | Good | Higher |
| Air movement | Generally better | More restricted |
| Suitable for | General insect exclusion | Smaller pest exclusion |
| Heat management | Easier airflow | Requires careful ventilation design |
Why Airflow Matters
If very fine insect netting is installed over large ventilation areas without considering airflow, the greenhouse can become hotter and more humid. This can affect crop growth and create conditions favourable to diseases. Farmers should therefore consider:
Pest exclusion + ventilation = effective insect netting system.
A fine mesh may provide better protection, but the greenhouse may need larger ventilation areas to compensate for reduced airflow through the mesh.
Selecting Nets to Prevent Thrips and Whiteflies
Whiteflies and thrips are both small insects, but their size and behaviour make them important considerations when selecting insect netting.
Whitefly Protection
Whiteflies are small enough to pass through relatively large mesh openings. Where whitefly exclusion is a major objective, farmers should consider fine insect-proof netting, rather than ordinary shade netting.
For whitefly protection, check for:
- Fine mesh construction.
- Consistent openings.
- UV stabilisation.
- Strong HDPE or suitable agricultural material.
- Good edge finishing.
- Manufacturer’s pest-exclusion specifications.
Thrips Protection
Thrips are even smaller and can be difficult to exclude completely. Where thrips pressure is high, a finer mesh may be required.
However, very fine mesh can reduce airflow, so the greenhouse ventilation design becomes even more important.
Installing Insect Nets on Side and Roof Vents
Side Vent Installation
Side vents are common entry points for insects because they are often kept open for ventilation. The insect net should cover the entire ventilation opening.
A typical installation involves:
- Measuring the ventilation opening.
- Cutting the net with enough allowance for fixing.
- Positioning the net evenly.
- Securing it to the greenhouse frame.
- Checking all edges for gaps.
- Installing a roll-up mechanism where required.
- Inspecting the finished installation.
The net should remain properly tensioned without being stretched excessively.
Roof Vent Installation
Some commercial greenhouses use roof or ridge ventilation. These openings should also be covered with insect netting where pest exclusion is required.
Roof vents can be particularly useful because warm air naturally rises. This allows hot air to escape while fresh air enters through lower openings. However, the insect net should be properly fixed around the entire opening.
Poorly installed roof netting can develop gaps due to wind movement.
Door Protection
The greenhouse door is another important pest entry point.
A greenhouse may have excellent insect netting on its ventilation openings, but if workers leave the door open, insects can enter easily. Good greenhouse design should therefore include a properly fitted door.
For higher levels of pest exclusion, some commercial greenhouses use a double-door or small entrance chamber. This creates a small transition area between the outside and inside of the greenhouse.
The basic principle is:
Outside → first door → small entry space → second door → greenhouse.
This reduces the chance of insects entering directly when workers move in and out.
Installing Insect Nets Alongside Greenhouse Polythene
The insect net and greenhouse film should work together without leaving exposed gaps and should be firmly secured.
Common fixing methods include:
- Aluminium lock channels.
- Wiggle wire.
- Suitable greenhouse profiles.
- Supporting wires.
- Clips designed for agricultural structures.
The exact fixing method depends on the greenhouse frame. The edges should be inspected carefully because even a small opening can become an entry point for insects.
Maintaining Insect Nets
Insect nets require regular inspection. Dust, soil and plant debris can accumulate on the surface and reduce airflow.
Farmers should check the net regularly for:
- Tears.
- Holes.
- Loose edges.
- Sagging sections.
- Damaged fixing points.
- Dust accumulation.
- UV degradation.
Pricing Per Square Metre and Roll Sizes
The price of insect-proof greenhouse netting depends on:
- Mesh count.
- Mesh opening size.
- Width.
- Length.
- UV stabilisation.
- Material quality.
- Manufacturer.
- Quantity purchased.
For budgeting purposes, farmers may encounter approximately Kshs 100-120 per square metre for agricultural insect netting, although actual prices vary considerably by specification and supplier.
| Net Type | Indicative Price Range |
| General insect netting | Kshs 100/m² |
| 40-mesh insect net | Kshs 100/m² |
| 50-mesh/finer insect net | Kshs 120/m² |
Common Roll Sizes
Insect nets are sold in different widths and roll lengths. Common insect net roll has a standard width of 3m and a length of 50m
UV Stabilisation and Lifespan
Because insect netting remains exposed to sunlight, UV stabilisation is important. Without adequate UV protection, plastic can become:
- Brittle.
- Weak.
- Discoloured.
- Easily torn.
A good UV-stabilised agricultural insect net can commonly provide around 3–7 years of service, depending on quality, exposure and maintenance.
| Factor | Effect on Lifespan |
| UV stabilisation | Improves durability |
| Strong sunlight | Gradually degrades material |
| Strong winds | Can cause mechanical damage |
| Correct installation | Reduces tearing |
| Regular inspection | Helps identify damage early |
| Cleaning | Maintains airflow |