Environmental Engineering Reference
In-Depth Information
may penetrate the plants before they dry off in the morning. Afternoon or
early-evening irrigation should be avoided whenever possible; turf-
grasses should be watered at times that assure that the leaf surfaces
will dry before nightfall.
The amount and timing of fertilization can greatly influence occur-
rence of turf-grass diseases. Typically, high levels of nitrogen increase the
risk of disease, but low nitrogen levels promote some of them, such as the
fungi Sclerotonia homoeocarpa on cynodon, zoysia grass and centipede
grass and Puccinia spp. on zoysia grass. Numerous diseases may also
become more severe when the plant suffers from deficiencies of nutrients,
especially potassium, calcium, phosphorus and magnesium.
Mowing practices can also affect diseases. Mowing creates open cuts
in the leaf cuticle, allowing pathogens an easy entrance into the meso-
phyll and allowing expansion within the plant. The risk of infection can
be increased even more when leaf tips are severed by dull mower blades
or when mowed turf-grass is wet and spores can readily move from
infected to healthy plants. Excessively low mowing height can also in-
crease disease occurrence by increasing stress on the turf-grass plants.
Usage of pesticides to control insects in turf-grasses may indirectly
influence activity of pathogenic fungi. Insecticides are often toxic to
saprophytic insects or other arthropods, and the disruption they cause
to the ecological balance may weaken turf-grass plants. Herbicides may
cause direct injury and therefore reduce plants' vigour and increase their
susceptibility to pathogens.
Chemical disease control
In tropical climates, sound management practices can prevent many
diseases from occurring on the larger scale, but sometimes chemical
intervention is needed to prevent excessive damage to high-value turf
areas such as putting-greens, tees and some sport fields. Turf diseases can
be controlled with fungicides, nematicides and fumigants. Fumigants are
used very infrequently and only on small areas such as golf greens or
tees, where diseases or nematodes have been present in the past and may
cause severe and long-lasting problems in the future. Other turfs in
tropical locations seldom undergo fumigation.
Nematicides are used more frequently but overall not often. They are
drenched into the thatch and soil and kill nematodes that come in contact
with the chemical. Besides nematodes they also kill numerous insects and
other soil fauna such as earthworms.
Fungicides, which kill or inhibit growth of fungi, are used quite
commonly. They should, if possible, be applied at the earliest stage of
the disease. This type of control, called curative , restrains the pathogen
after a mild infection has already become established, but turf areas that
have a history of developing a particular disease under certain weather
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