Diseases and Management of Crops under Protected Cultivation
Diseases and Management of Crops under Protected Cultivation
Diseases and Management of Crops under Protected Cultivation
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(<strong>Diseases</strong> <strong>and</strong> <strong>Management</strong> <strong>of</strong> <strong>Crops</strong> <strong>under</strong> <strong>Protected</strong> <strong>Cultivation</strong>)<br />
high wind velocity, glasshouse is discouraged.<br />
3.1.2 Polyethylene<br />
Plastic polyethylene is the most widely used greenhouse film around the globe. It is<br />
produced by mixing homopolymers <strong>of</strong> ethylene with or without an ultra-voilet (UV) inhibitor<br />
package but only UV stabilized polyethylene sheet is only recommended because non UV inhibitor<br />
package added polyethylene will break down after 3-5 months due to photochemical reactions.<br />
Polyethylene film is tough, flexible <strong>and</strong> relatively in expensive. It can withst<strong>and</strong> as low as -50C but<br />
80-90C temperature will cause it to melt. Above 60C it losses much <strong>of</strong> its strength <strong>and</strong> may<br />
stretch markedly. The life <strong>of</strong> UV stablized polyethylene film is 1-3 years. However, regidex<br />
polyethylene sheet may be used for 5-6 years on trench.<br />
3.1.3 Fibreglass Reinforced Panel(FRP)<br />
These panels consist <strong>of</strong> glassfibre reinforced polyester. The panels have been very popular<br />
in areas <strong>of</strong> high light intensity such as southern USA but about 10-15% heat loss due to<br />
increased exposed area makes it unfit for most <strong>of</strong> Indian region region. Further, with its age <strong>under</strong><br />
use, the transprency get reduced due to yellowing.<br />
3.1.4 Polycarbonate Panels.<br />
The panels are available in double skinned sheets. SDP polycarbonate sheets are similar<br />
in physical dimension to the SDP acrylite but are stronger <strong>and</strong> have a lower light transmissivity. Its<br />
price is approximately 25% higher than SDP acrylite.<br />
3.2 Construction Materials<br />
Besides glazing materials (Polyethylene/glass) several other materials are also requires for<br />
construction <strong>of</strong> a greenhouse. It is always better to prefer the use <strong>of</strong> locally available materials for<br />
the construction <strong>of</strong> a greenhouse. It not only reduces the installation cost but also help to<br />
popularize the technology. The major construction material required for greenhouse is its frame<br />
structure which could be either <strong>of</strong> a metal or wooden. Iron angle, GI pipes or alumminium frame<br />
are the most common metal used in greenhouses. Wooden frames can also be used which are<br />
locally available in the region. Such frames are cheaper than those <strong>of</strong> metal frames <strong>and</strong> also easy<br />
to use. Wooden frame should also be preferred in hilly regions since metal is a good conductor <strong>of</strong><br />
heat thus its temperature get reduced during winter months during summer it gets hot <strong>and</strong><br />
polyethylene sheet gets stuck to metal which tears <strong>of</strong>f the sheet. Sometimes supporting wares<br />
are also used in greenhouse to hold the polyethylene sheet. It is always advisable to avoid direct<br />
contact <strong>of</strong> metal with polyethylene sheet. If at all it is essential, gunny bags or cloth should be<br />
wrapped over the metal. Other precautions include use <strong>of</strong> smooth surfaced frame <strong>and</strong> removal <strong>of</strong><br />
sharp edges <strong>of</strong> frame. Strong foundation <strong>of</strong> frame is essential in cold arid region to resist the<br />
strong winds. Stability is further ensured by constructing earthern brick wall at the back <strong>and</strong> on<br />
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