Agriculture Reference
In-Depth Information
market of plastic anti-pest films for covering
the greenhouse that restrict the mobility of
some insects (affecting their vision) and that
hinder the development of diseases (e.g.
Botrytis
) are, also, complementary measures
of interest in IPM (see Chapter 4).
The use of pollinating insects (bees and
bumblebees) inside the greenhouse (Plates
25 and 26) has contributed to the rationali-
zation of integrated phytosanitary control, at
the grower's level, avoiding the use of harm-
ful pesticides (Meneses and Castilla, 2009).
The transfer of the greenhouse struc-
ture to another location, which was com-
mon for the tunnel greenhouse years ago
and that constituted a peculiar variant of
crop rotation, was efficient in the fight
against soil-borne diseases. Nowadays, soil-
less cultivation can be an easier alternative.
others (
Pythium, Phytophtora, Alternaria
).
Soil-borne diseases, in general, are favoured
by high temperatures (Louvet, 1984).
The usually high humidity inside green-
houses, at least at certain periods of time,
favours the formation of fungal spores, accel-
erating their development, as well as the
growth of bacterial colonies, especially if
temperatures are favourable. These risks
become higher when water vapour condenses
on the plants. Therefore, indirect prevention
methods include procedures that decrease
the environmental humidity, such as the use
of drip irrigation and mulching the soil.
The wind is limited inside the green-
house, except in greenhouses with mechan-
ical ventilation, which limits the dispersal
of disease inocula.
13.6
Most Common Greenhouse
Diseases
13.5
Climate Control and IPM
Viruses, bacteria, fungi and nematodes can
cause diseases in greenhouse crops. Fungal
pathogens are the main cause of disease, most
frequently species in the genera
Fusarium,
Pythium
and
Phytophthora
, among those of
soil origin (Gómez, 1994). Nematodes or bac-
teria cause other soil-borne diseases. Bacterial
diseases are difficult to control, because there
are very few efficient products, so it is essen-
tial to prevent these by means of disinfecting
the root medium, among other measures.
Among diseases that affect the aerial organs of
plants we may highlight
Botrytis
(Photo 13.4),
Phytophtora, Pseudoperonospora
and
Scle-
rotinia.
Table 13.2 summarizes the most com-
mon diseases.
Climate factors directly affect the develop-
ment of pests and diseases of crops, and so
an appropriate greenhouse climate control
can help to decrease their development.
Avoiding water condensation on the plants
avoids the proliferation of
Botrytis
. The ambi-
ent humidification, to increase the RH, contrib-
utes to the fight against
Oidium
and hinders the
development of spider mites and thrips.
On the other hand, the improvement of
the thermal conditions in greenhouses, the
absence of rain (inside greenhouses) that
washes the phytosanitary products (in the
open air) and the filtering of UV light of
some plastic covering materials contribute
to an increase in the efficiency of the treat-
ments although they could also increase the
risk of phytotoxicity (Urban, 1997a).
Alteration of the solar radiation inside
the greenhouse can influence the develop-
ment of diseases, not just due to the effect on
the spectral composition of the radiation that
affects the formation of fungal spores, but
also due to the higher sensitivity of plants to
diseases at reduced light levels, as is usually
the case in dense crops (Louvet, 1984).
Inside greenhouses, the temperatures
are usually higher than outside, limiting the
development of some diseases (
Cladospor-
