Agriculture Reference
In-Depth Information
the hygiene and safety of the staff working
in the greenhouses. The increasing interest
of consumers in health and food safety has
contributed to improved risk prevention
mechanisms in the use of pesticides.
threshold. Although biological control has
been known about for more than half a cen-
tury, its use had not expanded until a few
decades ago (Blom, 2002).
The biological control of diseases is not
widely used in practice. Techniques that may
be highlighted include: (i) crossed protection
techniques (where the organism that arrives
first to an infection point acts against the patho-
gen that arrives later; this is used for the control
of tobacco mosaic virus (TMV) by inoculating
the plant with an innocuous form of the virus);
(ii) induced resistance (the organism arriving
first induces a defence reaction in the host);
(iii) passive occupation (previous occupation of
the infection point by an innocuous organism);
and (iv) hyper-parasitism (
Trichoderma
).
However, it should be pointed out that there are
many other techniques (alelopathy, antibiosis)
of possible use (Jarvis, 1997).
The use of biocontrol agents has been
efficient against some diseases such as the use
of
Trichoderma
against
Pythium, Fusarium
and
Rhizoctonia
(Elad, 1999).
The pest's natural enemies, besides not
competing for the resources, carry out a
predatory activity, feeding on the pest spe-
cies. Parasitoid insects carry out a particular
parasitic activity (external or internal ovipo-
sition of one egg on the host, from which a
larva emerges that eats the animal as it devel-
ops). Parasitoids are more specific (monopha-
gous in many cases), whereas predators are
usually polyphagous (García, 1994).
The use of entomopathogens in biological
control in the greenhouse, as an insulated
enclosure, is of special interest. The massive
use of
Bacillus thuringiensis
for the control of
Lepidoptera has expanded, whereas the use of
other pathogens, such as
Verticillium lecanii
(limited by the optimum temperatures range,
Photo 13.1) or
Archensonia
(for white fly) and
Beauveria
or
Paecilomyces
(for white fly,
aphids or thrips) is not so widespread (Parrella,
1999). At the time of writing this text, in Spain
only the use of
Beauveria
is authorized,
although the registration process for
Verticillium
and
Paecilomyces
is in progress
(J.V.D. Blom, 2007, personal communication).
Table 13.1 summarizes the main natural
enemies of the most common greenhouse
pest insects in Spain (Photos 13.2 and 13.3).
Pesticide application methods have a great
influence, both on their efficiency and on
the labour costs. The application methods
depend on the vehicle used to distribute the
pesticide: (i) dust, when a solid is used (e.g.
talc); (ii) spraying and fogging, when a liq-
uid is used (usually in water); and (iii) fumi-
gation when a gas is used.
The majority of horticultural treatments
consist of spraying solutions or suspensions
of the active materials. The most usual
greenhouse sprayings are performed with a
motor, provided with hoses and pistols to
cover all areas of the greenhouse and direct
the spray to the desired points. The service
pressure must be sufficient to achieve a very
small droplet size and to generate turbu-
lence that helps the product cover the whole
canopy (Aranda, 1994).
The ultra-low volume systems use a fan
and a fog mechanical generator in associa-
tion with each other, to obtain a very small
droplet size and great canopy penetration,
which allows for treating large areas from a
fixed point. If located over a mobile trolley
they can be operated in pre-fixed locations
(as a semi-fixed system).
The thermo-foggers cause a very fine spray
(of less than 100 mm diameter) by the explosion
of a mix of fuel and air (Urban, 1997a).
Among the mobile automatic systems the
most common is a treatment trolley that moves
automatically along guiding pipes (also used
for heating) between the crop rows.
13.3
Biological Control
Biological control is based on the use of
natural enemies of the pests (parasitoids,
predators and pathogens) to maintain their
infestation below an economic damage
