Environmental Engineering Reference
In-Depth Information
The aim of prevention is to minimize weed introduction within the
turf area. Weeds are prolific seed producers and can easily be spread by
wind, water and animals or with contaminated planting material. Use of
weed-free turf seeds, stolons, sprigs, plugs or sod is the most basic
defence against weeds. As mentioned in Chapter 3, most national or
local governments set limits on the contamination of seeding material.
The limits vary from location to location, but most are below 1%, and all
commercially distributed seeds must bear a seed label that provides the
actual percentage of weed seeds in the package. In many countries,
similar regulations with respect to vegetative materials are also estab-
lished and enforced. Sod produced by sod farms is monitored by appro-
priate national or international sod-producers associations and in most
cases should not contain more than 1 weed per 1 m
2
, but in some cases no
weeds are allowed. For example, cynodon in St Augustine grass sod is
completely forbidden because after establishment no cultural, physical or
chemical method will eliminate it.
Another main form of weed prevention is sanitation practices. Mech-
anical devices, such as mowers or cultivators, easily transport weeds
from place to place, especially when turf is wet. As a general rule, less
weedy turf should be mowed before weedier areas, and the equipment
should be rinsed before being transported from weed-infested to weed-
free areas. Frequently, weeds are introduced into the turf through the
addition of contaminated topsoil. When weed-contaminated topsoil is
used for top-dressing, adequate chemical control should be conducted
before weed seeds germinate. Another contributor to the spread of
weeds is irrigation systems drawing water from open ditches or ponds.
Areas around ponds should be mowed and kept as free of weeds as
possible.
Cultural practices that encourage robust and healthy turf are a very
important but often neglected way of keeping turf free of weeds. Because
many weeds need intense light for germination, high turf density may
reduce their germination by preventing sufficient light from reaching the
soil surface. All cultural practices that promote vigorous growth of turf-
grasses, such as proper soil moisture, adequate fertilization, favourable
pH and good aeration, help to make turf resistant to invasion by weeds.
By the same token, any major stresses such as excessively low mowing
height, insects, diseases or excessive shade, reduce turf density and allow
weed encroachment.
Other significant means of weed control are tillage before turf estab-
lishment, hand pulling, hoeing and mowing. These methods are often
categorized as mechanical and, especially when supplemented with cul-
tural practices, provide quite satisfactory results.
Tillage, or cultivation, is usually conducted before turf-grass estab-
lishment. Weeds are removed or buried by the process, or are uprooted
