Environmental Engineering Reference
In-Depth Information
conditions are often sprayed before disease development. This type of
control is called
preventive
; it restrains the pathogen before it enters the
plant. Because of environmental concerns, continuous preventive disease
control is highly discouraged, but it is nevertheless still practised on some
golf courses, where broad-spectrum fungicides are applied throughout
the year.
Fungicides that protect turf-grass against infection can be grouped
into two types:
contact
and
systemic
. Contact (non-systemic) fungicides
kill spores and mycelium on the surface of the turf-grass plant. Because
turf is subject to mowing as well as wash-off by irrigation and rainfall
water, contact fungicides are usually effective for no more than several
days. In contrast, systemic fungicides are appliedmostly to the soil and are
then absorbed and translocated throughout the plant vascular system,
where they kill growing fungus as it penetrates the plant. Because of
their residual activity and internal action, systemic fungicides are effective
for much longer than contact fungicides, often for several weeks. Systemic
fungicides are usually formulated for application as a spray or granules.
Because many of them are absorbed primarily by the root system, liquid
forms should be applied in fairly large volumes of water or watered in
immediately after spray application. Granular forms should be applied
prior to irrigation or rainfall. On the other hand, all contact fungicides are
formulated to be sprayed. The volume of water is typically higher than for
herbicides and ranges from10 to 15 l of water per 100 m
2
(1000-1500 l/ha).
Disease-control programmes should never depend upon fungicides
alone. Disease-management procedures are meant to complement rather
than displace one another. Selection of proper cultivars, best manage-
ment practices and occasional use of chemicals guarantee healthy and
vigorous turf.
Insects
Insects are the most abundant animals living on earth. Most of them
decompose organic matter, and the large majority are entirely harmless.
Some, however, are significant pests of plants and animals.
The usual description of insects as six-legged, segmented creatures
with their skeletons on the outsides rather than the insides of their bodies
actually applies most often to adult insects, which in many cases live only
to reproduce, do not feed and cause no damage. During their life cycle,
insects undergo a series of changes called
metamorphosis.
For some in-
sects, metamorphosis is complex, and for others it is simple (Fig. 11.9).
The former begin life as eggs, which hatch into larvae, which in turn
become pupae, and finally reach the adult form. In insects with simple
metamorphosis, the eggs hatch into nymphs that resemble adults but are
