| 'Smart' Polythene Film is the term given to XL Horticulture's range
of horticultural polythene. Find out more about this top of the range
Polythene ......
Contents -
Polythene Film History…
To understand what 21st Century Polythene technology means to the Horticultural
industry, it's worth looking back in time to the late 60's, early 70´s.
Polytunnels were then little more than ‘walk in’ cloches (or
‘crawl in’ to be more precise), restricted in height, width,
and length by the Polythene extruder's ability to produce big enough films.
Consequently if you were lucky enough to fit a sheet without it splitting
you could look forward to a growing environment that fell well short of
ideal. The good news was that the cover only lasted two years !! by which
time you could have made a down payment on a glass house.
Little wonder things changed, Polythene got wider, Polytunnels got bigger
and Multispans were born. Some Polythene manufacturers included surface
coatings to reduce condensation. Thermal Protection Tape and better quality
mix and extrusion gave a much longer life span. So there it was, the late
1980's and Polytunnels became the professionals choice with a basic standard
of Polythene cover which is still available today, some good and some
not so good.
With so much professional commitment to the use of Polytunnels by growers
worldwide, it was inevitable that as technology became available it would
be used to benefit the tunnel grower.
XL Horticulture´s range of ‘Smart’ Polythene
Film …
XL Horticulture have produced a range of growth manipulation ‘Smart’ films :
- Solar Filter Films to produce better plants by exploiting their
natural growth triggers
- UV Blocking Films to reduce the spread of disease and pests like
Botrytis, Mildew and Aphids
- High Diffusion Films which scatter the light to reduce shadows
within the growing house
- Heat Reduction / Heat Retention Films for better temperature control
- Anti Condensation and Anti Surface Algae Films to maximize light
transmission
All of the above properties are brought together in the smartest of ‘Smart’ films, ‘Sterilite ®
What the Grower Magazine had to say in a recent article …
Thumbs up for Smart Films
Reproduced by kind permission of The Grower
Peter McGrath reviews progress with new age films for crop covers
Research into different materials and additives for polytunnel covers
has produced a range of high-tech films with different characteristics.
These additives either block or allow through different wavelengths of
light, a process known as spectral modification, which creates biological
effects on the plants, pests and diseases growing beneath them.
Already near or actually on the market are films that claim to reduce
the disease incidence of botrytis and other diseases, and the plant height
of ornamentals. Although these 'new-age' films can be 5 to 30% more expensive
than the conventional alternatives, growers can benefit because of the
reduced need to apply fungicide and plant growth regulation chemicals.
Both Visqueen and XL Horticulture - leaders in the development
of 'smart' films - offer a thermal heat block (THB) film. These
contain an additive which 'scatters' the visible wavelengths of light
as they pass through. The films also block heat-producing infra-red rays,
so reducing the chance of plants becoming scorched.
"This allows us to achieve two things", says Visqueen's technical
director Dr Richard Henbest. "The scattering effect means we can
get more light into the glasshouse or polytunnel and, by making it more
diffuse the photosynthetically active visible light is more available
to the plants."
First marketed in France Visqueen's Luminance THB has been available
in the UK for the past couple of years. Last year XL re launched
its Sterilite THB film with new specifications.
The main difference between the two films is down to a trade off. The
greater percentage of the valuable diffused light which penetrates further
into a crop's canopy, the lower the total amount of light that enters
the polytunnel Luminance THB transmits 88% of photosynthetically active
light, of which over 90% is diffused. In comparison, SteriLite THB allows
through 91% of the light (89% guaranteed minimum), of which 62% is diffused.
Richard Henbest says: "Under most growing conditions, trials show
that we can get about a 10% increase in the growth rate of ornamentals
under our Luminance THB film".
According to Les Lane, in order to create viable spores, most
fungi need the stimulus of wavelengths in the ultra-violet range of light,
between 350 and 380nm. "All polythene and glass block up to about
350nm, but if you take out light up to 380nm you can stop diseases from
spreading", he says. XL's Sterilite HDF, for example, is claimed to reduce levels of both botrytis and
powdery mildew and can be used over four seasons.
Insects too
Research from Israel also suggests that UV-blocking films - in this case
made by Israeli company Ginegar Plastics - can control insects such as
thrips and whiteflies and the viruses they transmit.
Les Lane also claims that Sterilite films can help control aphid
populations. "We tested it on pansies in our own nursery," he
says. "In three or four spots we had colonies of about 30 to 40cm
across but they didn't spread throughout the house as they would normally
have done." The reason for this, he believes, is that many insects
use UV light for navigation.
By blocking the UV to 380nm, the insects are dissuaded from moving around.
"But we want SteriLite to be part of an IPM system," adds Les
Lane, "so we only block the light to 380nm. We have anecdotal
evidence that beneficial insects move around during the brightest part
of the day and do the work they have to do."
Blocking the UV light to 400nm could cause problems, claims Les Lane,
as they can see just 20% of the light available to them, compared with
60% if it is blocked to 380nm.
"It was a consideration that we would get substandard pollination,"
admits grower Angus Davison, MD of Haygrove Tunnels and chairman of Kentish
Garden, "but so far we have not found it to be a problem." He
believes the main reason is that trials with Visqueen's Anti-Botrytis
and XL's SteriLite film used tunnels with high legs that were not sealed
in the middle, so bees had enough natural light available for navigation.
Growth regulation
Other films work by screening out light at the red end of the spectrum,
around 650nm. XL's Super Green and Super Blue and Visqueen's Solatrol
films all adjust the ratio of red to far-red light, with pronounced effects
on the morphology of plants. However they have been designed for different
uses. XL products, for example, are used as tunnel covers. Super
Green has been available for several years as a film suitable for growing
plants which prefer a shady environment, and Super Blue covered tunnels
are being tested commercially for the first time in the UK this year.
In contrast Solatrol is recommended for use within tunnels and glasshouses
as an internal screen between the light source and the crop during just
part of the growing season. HDC funded trials carried out at the University
of Reading, have shown that the control of plant growth was not consistent
enough to be able to eliminate the use of growth regulators. However in
other trials Solatrol has been used successfully over pansies and poinsettias.
Although it is not yet commercially available, limited quantities of Solatrol
are available for evaluation purposes.
What's next?
XL Horticulture has already introduced films containing metalocene,
a co-polymer that adds extra strength to the polythene. This means that
the films can be made thinner and lighter.
The new 600 gauge films are 150 microns thick compared to the more typical
180 micron, 720 gauge films. Adding metalocene also makes the films 50%
more resistance to tearing claims Les Lane. XL will also
soon be trialing anti-algae film.
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