FILM STARS

This article appeared recently in Horticulture Week and is reproduced here with there kind permission.

Polythene films have come a very long way, boosting yields and mimicking chemicals, says Sally Drury.

REDUCING TEMPERATURES, PROVIDING growth control, eliminating botrytis or providing a safe environment for the public - choosing the right cladding for your polytunnels is no longer just a question of thickness or cost.

Polythene film technology has advanced dramatically in the past decade and developments continue to benefit plants and growers as new products come to market.
One of the first “new age” products developed for growers was thermal heat block film – marketed as BPI Agri’s Luminance THB and Sterilite from XL Horticulture. It reduces the amount of infrared light - the heating rays – entering a polytunnel, reducing the temperature inside.
Passing through Luminance THB, incoming light is scattered, improving the efficiency of photosynthesis and increasing plant yield and quality. These benefits have been demonstrated at the University of Reading (HDC report 150) and in commercial trials.
Technical Director Richard Henbest, of BPI Agri, in Stockton on Tees, says: “Results from Haygrove Fruit Farm have shown that temperature inside the structure can be cut by up to 6 degrees Celsius in comparison with a standard UVI/EVA film, and data from France and Spain has shown reductions of up to 10oC. These results have implications for temperature sensitive crops, even in the UK.”
Although the major trials of THB films have involved salad and fruit crops, showing average fruit size increases of 26 percent in strawberries, the films can equally benefit ornamental crops. Growth rate of ornamentals that are raised under Luminance THB can be increased by as much as 10 percent.

The anticipated restrictions on chemical growth control means smart films offer real benefits to bedding growers. Products such as XL Horticulture’s Supergreen and Superblue, and BPI Agri’s Solatrol films, adjust the ratio of red to far red light, with dramatic effect on plant morphology.
“Solatrol reduces the amount of far-red light, the part of light that produces leggy plants, relative to the amount of red light – the part that shortens plants. The result is reduced internode length. Plants are produced of equal quality and height without the use of growth regulating chemicals,” says Henbest.
Commercial trials with Solatrol have shown it to be effective on over 35 species and 76 cultivars. A trial at Needham Growers, in West Sussex, involved growing nine different species of bedding plant under the film and comparing them with the same species grown under normal commercial practice using chemicals.
“The results demonstrated no significant differences in plant height between the two treatments when plants were despatched to customers, indicating that Solatrol can replace chemical growth regulation,” says Henbest.
Trials are set to continue at H R Whetman, a specialist hybrid pink and dianthus grower in Devon, and with the US Department of Agriculture and the University of Georgia. Development work is continuing and two new versions of Solatrol are available: a 50-micron screen film for use in glasshouses and a film of 150-micron thickness for French and Spanish tunnels. Both are effective for two seasons.

Light is also implicated in the development and spread of pests and diseases, so it is not surprising to find companies working on the agronomic benefits of using films that absorb a broad waveband of ultra-violet light.
“UV light can trigger spore production of botrytis and downy mildew and is important in insect vision, so removing a greater part of the UV can help to reduce diseases and insect infestation,” according to Henbest.
Sounds good, but the development of such films has not been without problems. The additives that absorb UV diffuse slowly from the film and can be destroyed by photo-oxidation, progressively reducing the absorption properties. However, the discovery of a new absorber, which uses a different mechanism and maintains constant UV absorption has led to the introduction of Luminance UVX by BPI Agri. This product has the same high diffusion and heat control properties as Luminance THB.
Sterilite films from XL Horticulture have also been shown to reduce botrytis and powdery mildew and to help control aphid populations.

And there’s good news for garden centres and retail nurseries. Having taken several years to perfect, Freva is a polyethylene, flame retardant film developed by BPI Agri specifically as a cover for retail areas and for polytunnels where public access is necessary – providing an alternative to PVC flame retardant films.
Offering high light transmission (83-85 percent) and enhanced diffusion characteristics, Freva provides a good environment for plants. To meet fire regulations it is also certified to BS 7837:1996. This is the test whereby a flame is applied for 10 seconds to the bottom edge of the film. To pass the test, no burning debris should occur and any flaming should cease within five seconds of the flame being removed. When Freva was tested, not only was there no burning debris, but the film also indicated no measurable flaming.
Freva has additionally been tested to BS 5438 : 1989 tests 2A and 2B and has been shown to meet the requirements of BS 5867:1980 part 2 performance level B. It also meets the German standard DIN 4102-1 Building Class B2 and fire certification is now being pursued in other European countries.
“We are delighted that we have finally succeeded in producing a flame-retardant film. It has taken an enormous amount of time and research to produce a film that is cost effective, efficient and above all safe,” says BPI Agri Sales Director John Phoenix.
All indications are that the flame retardant additives used in the polyethylene film have no adverse effects on the weathering characteristics and life expectancy of the film.
A lifetime of three years is, therefore, guaranteed, but – bearing in mind that garden centres are not usually subject to the most aggressive of weathering conditions – a longer period of use can be expected.
Freva is available in widths of 9.20M, 12M and 14M. Its thickness is 180microns.


DATE: 10/06/2003