Among insect control methods,
physical barriers continue to play a significant supporting role today
and are likely to have a significant role in the integrated pest management
(IPM) programs of the future. The use of UV-blocking cladding materials
can play a part in IPM programs fro crop protection in greenhouses
because they are compatible with the use of biopesticides and natural
enemies.
The UV-blocking films act as a photoselective barrier that modifies
the greenhouse environment and disrupts the normal insect behavior
so as to discourage pest activity. As a consequence few insects invade
these structures and the opportunity for virus transmission is reduced.
Although most of the plastic films contain UV-absorbing properties
to extend the life of the material, only a few plastics are available
on the market to block over 95% of light transmission in the range
between 200 to 380 nm while allowing 80% transmission of photosynthetic
active radiation (PAR).
The blockage of UV radiation interferes with insect vision, navigation,
orientation and feeding behavior causing a significant reduction in
population density and dispersion of insect pests such as aphids,
thrips and whiteflies. UV-absorbing films also acted as an inhibitor
of Myzus persicae (Schulzer) propagation and dispersal by reducing
its flight activity.
UV-absorbing films are effective in reducing insect transmitted viral
diseases. A significant reduction in virus spread has been observed
in Bemisia – transmitted viruses such as tomato yellow leaf
curl virus (TYLCV) and cucurbit yellow stunting disorder virus (CYSDV)
in tomato and cucumber crops, respectively.
The significant decrease in the spread of these viruses has been attributed
to the impairment of whiteflies to fly and disperse in the absence
of UV-light.
Most of the information related to the effects of UV-light absorbing
plastic films on insect populations and virus spread has concentrated
in tomato and cucurbits. To our knowledge, there is no information
on the impact of UV-absorbing plastics on insect pests and virus diseases
commonly found in lettuce crops grown under greenhouse environments.
The aim of this work was to study the population dynamics of insect
pests and the spread of insect-transmitted viruses in a lettuce cop
grown in a greenhouse covered by a UV-light absorbing films on the
growth and yield of lettuce as well as the mean temperature inside
the greenhouse was compared to that obtained when using standard polyethylene
films.
Plastic films tested. Two types of plastic films were used for comparison:
a UV-absorbing film (AD-IR AV clear manufactured by Ginegar Plastic
Products Co., Ginegar, Isreal) and a non UV-absorbing film (control)
standard polyethylene plastic film commonly used at the experimental
site and called Astrolux (Hyplast Ltd., Hogstraten, Belgium). Both
Types of plastic films had similar physical properties Both Types
of plastic films had similar physical properties (thickness, anti-drip,
anti-dust, thermicity, visible light transmission and diffusion) except
for their ability for UV-blockage. The light transmitted for both
plastic types was measured experimentally at the beginning and at
the end of the three lettuce growing seasons. The amount of UV (250
to400 nm) and visible light (400 to 700 nm) transmitted by both plastic
types was measured using a spectroradiometer (models UVM and BQM,
respectively, Spectrum Technologies, Apogee Instruments, Logan, Utah).
Measurements were taken inside and outside the plastic tunnels by
placing the sensor perpendicularly to open sunlight in a sunny day
at 12: HR with an outside air temperature of 15°C.
A 2 year experiment was carried out in Northeastern Spain(Navarra)
to evaluate the impact of a UV-blocking film (AD-IR AV) on the population
density of insect pests and the spread of insect-transmitted virus
diseases associated with head lettuce [Lactuca sativea (L.)]. Results
showed that the UV-absorbing plastic film did not loose its ability
to filter UV radiation after three lettuce crop cycles (14 months).
The UV-absorbing plastic film was effective in reducing the abundance
and in delaying the colonization of lettuce by aphids [Macrosiphum
euphorbiae (Thomas) and Acyrthosiphum lactucae (Passerini)]. A significant
increase in the percentage of marketable plants was achieved under
UV-absorbing films due to a reduction in the number of plants infested
by aphids and by insect-transmitted virus diseases (mainly potyviruses).
Also the UV-absorbing plastic films were effective in reducing the
population density of Frankliniella occidentalis (Pergande) and the
spread of tomato spotted wilt virus (TSWV) as well as the population
density of the lepidopteran pest, Autographa gamma (L.), a common
pest of lettuce in Spain. However, no effective control of the greenhouse
whitefly Trialeurodes vaporariorum (Westwood) was achieved. The results
showed that UV-absorbing plastic films are a very promising tool to
protect greenhouse lettuce from the main pests and insect-transmitted
virus diseases occurring in northeastern Spain.
