Environmental Engineering Reference
In-Depth Information
typical spots or lesions appear on the individual blades, but in other
cases, the entire leaf blades are affected. Sometimes symptoms are typical
from the beginning, but sometimes they are overlooked because frequent
mowing tends to destroy early evidence of the disease and only more
severe, advanced symptoms are noticed.
If the turf-grass manager has difficulty with identification of a par-
ticular disease, the local plant-protection service or plant diagnostic clinic
should be contacted. Local diagnosticians and plant pathologists are
often most knowledgeable about the current disease problems in their
own areas and can often help to diagnose diseases from descriptions of
the symptoms. If not, or if the problem is severe or persists for a long
time, turf samples should be delivered to the appropriate laboratory.
Samples should include both healthy and unhealthy turf, should be
taken at an early stage of disease development, should be about 10 cm
in diameter, and should include at least 5 cm of roots below the thatch.
The turf samples should be accompanied by information about recent
weather conditions, cultural practices, fertilization and pesticide applica-
tions; photographs might also be provided.
If nematodes are the suspected cause of turf disease, their presence or
absence must be confirmed before pesticides are used. Because nemati-
cides are profoundly toxic, their application should be avoided unless it
is essential, so nematode presence and count must be determined
through accurate laboratory diagnosis.
In the tropics, disease management is generally less challenging than
management of weeds or insects. Warm-season turf-grasses are much
more disease resistant than cool-season species and, if they are infected,
damage is usually less profound and relatively easier to control. In the
arid and semi-arid tropics, fungal diseases are rarely a major problem. In
the humid tropics, they are more common and usually develop in areas
subject to additional stresses. Diseases caused by nematodes are rela-
tively rare but much more common than in temperate climates. Nema-
todes are very plentiful in the soil. For the most part, they are harmless
and feed mainly on fungi or bacteria, but some species can infect turf-
grass roots, impair growth of the plants, and make them look chlorotic
and wilted. Severity of disease usually depends upon the number of
parasitic nematodes present in the soil.
Methods of disease control
Like weeds, diseases in turf can be controlled by means of prevention,
development of resistant cultivars, proper cultural practices and
chemical interventions. The principal means of prevention is minimizing
introduction of pathogens into the turf area. Sanitation of seeds,
