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In Mediterranean climates we plant tomatoes and peppers almost all year round. In spring and especially in summer there are very high temperatures with very high amounts of light radiation. These conditions can create a great amount of stress on both seedlings and plants resulting in lower yields. Shading methods have been developed over the years to allow the plants to grow under better conditions and thereby improve the quality and yields of the crops.
Advantages:
1. Black net is cheaper, easier to maintain and operate as compared to 50 mesh net.
2. It is less humid under netting as compared to 50 mesh net. The air flows more freely, air temperatures are lower as are leaf/plant temperatures. and overall it is easier to create a better environment for the plant growth.
3. The shade percentage remains more stable than 50 mesh nets because the dust that adheres to the net does not increase the shade percentage because the net is black.
4. Netting prevents the penetration of pests such as Heliothis, Prodenia, Laphygma, Plusia amd Agrotis.
5. Provides protection against hail and reduces damage from radiation frost, sun burn and wind compared with plots grown without protective net.
Disadvantages:
1. A range of pests are able to penetrate the net such as; tobacco whitefly, aphides, western flower thrips, mites and leaf borer flies. Some of these pests are vectors of diseases and viruses and may cause much damage to the crop.
2. Suitable for spring/summer crops and not suitable for autumn/winter crops, since these nets are not able to accumulate the heat required in the structure for the development of the plants in autumn/winter.
1. Provides effective protection against most pepper and tomato pests, including tobacco whitefly, aphides, borer flies, moths and significantly reduces penetration of thrips and mites, compared with shade netting.
2. When the net is clean it provides 25-35% shade.
3. Provides protection against hail and reduces damage from radiation frost, sun burn and wind compared with plots grown without protective net and shade netting.
4. Suitable for late summer plantings and is better in autumn/winter than shade netting as these nets are able to accumulate heat better than shade netting.
Disadvantages:
1. Air flow within the structure covered with 50 mesh nets is relatively poor resulting in relative increase in humidity in the structure. This makes it more difficult for the plant to lower the temperature around it (which is based on the photorespiration process). In addition, the risk increases for the development of leaf diseases, which develop well in relatively high humidity conditions.
2. Heavy heat load in summer is liable to cause faulty fruit setting.
3. These nets tend to collect dust over the course of their life, resulting in rising shade percentage, which may reach up to 50% shade. This is not desirable during the autumn/winter season, when the radiation is low and is required for the growth of the plant.
Light:
1. The light used in photosynthesis is called PAR (photoactive radiation) and it is measured in units of micro-Einstein. There are light meters available to measure the PAR light. 2.
2. Tomatoes give good yields and quality when the PAR is 405-700 micro-Einsteins, whereas peppers require between 800-1200 micro-Einsteins for optimal photosynthesis.
3. If on a summer’s day the light radiation is 2000 micro-Einsteins then if there is 30% shading there is enough light for most of the day for both tomatoes and peppers.
4. The grower of tomatoes and peppers wants to have as many daylight hours as possible within the micro-Einstein ranges mentioned above. When light levels are below the optimal levels mentioned above then the photosynthetic rate decreases and the yield and quality will suffer.
5. Black shade net of 30% will give many hours a day of good sunlight for photosynthesis and also provide the physical protection as listed above.
Tomatoes under Black Net:
1. If the structure is strong enough to support the crop then Dutch trellising can be used. With Dutch trellising, double rows can be used with normal plant spacing of 40-50cm. Single rows can also be used with plant spacing of 30-40cm and the rows spaced 110-150cm.
2. Spanish trellising can be used in all structures of black net. In Spanish trellising single rows are used. The distance between plants in the row can be between 30-40cm and the distance between rows is 110-150cm. The plants are usually grown on single stems but can also be grown on double stems. The heads are cut when the plants reach the top of the stakes.
3. White fly can easily enter any net-house that is not covered with 50 mesh anti-insect net. Therefore, if the disease TYLCV (Tomato Yellow Leaf Curly Virus) is found in the growing area then only grow varieties with good tolerance to the disease.
Peppers under Black Net:
1. If the structure is strong enough to support the crop then Dutch trellising can be used. Double rows are used with plant spacing within the rows at 30-40cm.
2. Spanish trellising can be used in all structures of black net.
In Spanish trellising single rows are used. Spacing is 30-40cm within the row and 110-150cm from row to row.
New colored nets:
1. The colored nets help manage the light spectrum and have special optic properties enabling exploitation of the sun’s rays.
2. For example: three shade net structures for pepper crops with the same 30% shade were compared. The colors of the nets were red, black and pearl. The results achieved were that the pearl nets provided better protection against diseases and viruses compared with the other nets tested. Nonetheless, the plants grown under the red shade netting attained higher yields than the other nets.
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