A recent two day conference organised by the National Turfgrass Council (NTC) and the National Association of Agricultural Contractors (NAAC) brought together experts and practitioners in the Amenity Management Sector to discuss and learn about current methods and new directions in the control of weeds and other pests on amenity land.
What are the options?
Alan Cathersides of English Heritage stressed that as
a public body, English Heritage prefers not to use chemical herbicides or other
pesticides wherever possible. Extensive use of mulching effectively controls
annual weeds on borders and shrubberies. However, the control of particularly
problematic perennials requires the judicious use of herbicides.
Some of the most difficult perennial ‘weeds’ to control,
such as Japanese knotweed and giant hogweed, were introduced to this country as
ornamentals but have adapted rather too well. Given adequate space these plants
can develop into impressive features, and growth control, as opposed to
eradication can be achieved by removing flowers before seeding.
Ground elder, couch grass and bindweed can be physically
removed if caught early, but established infestations are virtually impossible
to pull out, and also difficult to spray selectively without affecting desirable
plants. Heavily infested beds are best cleared by splitting and removing the
rhizomes, or, less desirably by total spraying with a non-selective herbicide
and replanting.
Bracken stands can be important in providing shelter for
young deer and are a habitat for the rare High Brown Fritillary butterfly. Where
control is needed, repeated cutting can be successful. Docks similarly can be
controlled by repeated cutting and if caught early enough can be pulled up. They
are also most troublesome in weakened grass swards which can out-compete the
docks in favourable conditions. Total and immediate eradication of the above
weeds from sites can be achieved by using correctly timed and careful
application of the right herbicides.
Speaking on woodland and scrub maintenance, Colin Palmer
stressed not only the importance of choosing the right herbicide for the job,
but also of ensuring that it may legally be used for the job. Two other
important points made were that certain herbicides may damage non-target species
(the example of terbuthion+picloram on trees) and that in some situations it
must be accepted that no effective chemical solution is available.
What besides herbicides?
Peter Stanley of Birmingham University reported how
arisings (e.g. plant cuttings and leaves) from grounds maintenance operations
have been successfully used to suppress weed growth and enhance landscape
features on the University grounds.
Dr. Roger Smith of the University of Newcastle-upon-Tyne
explained that the features of amenity grassland can be dramatically influenced
by management strategies. Low fertiliser regimes and high pH encourage legume
and broad leaved weeds while high fertiliser regimes and low pH allow grass
varieties to out-compete these species. Where natural grassland meadows are
being maintained or encouraged, cutting time is crucial in allowing seeds to
ripen and drop thereby ensuring varied wild flower stands. Similarly, where a
tendency for scrub species invasion exists, grazing in spring and autumn can
keep scrub off grasslands.
Dr James Hitchmough of the Scottish Agricultural College,
Auchincruive, gave several examples from around the world where amenity grounds
maintenance regimes did not rely on herbicides. In Australia there has
apparently never been extensive use of residual herbicides, but tons of mulches
have consistently been applied which suppress annual weeds. In some parts of
Holland, far from dousing railway lines with herbicides grass is grown between
the tracks. Other techniques include using subsoil or topsoil taken from below
the surface for plantings: these soils contain less seeds. Planting types and
species can influence weed invasion: woodland, woodland edge shrubs and meadow
are plantings which resist weeds or carry them unobtrusively, and are cheap to
maintain; species which create dense ground cover or ground shade will also
suppress weed growth.
Turf decisions
Two speakers from the Sports Turf Research Institute
emphasised from different perspectives the fundamentals of turf maintenance. If
adhered to conscientiously, the need for pesticides could virtually be
eliminated. To begin with resistant and dense grass species should be chosen
which are suitable for their growing environment and for the use to which they
will be put. Soil conditions, in particular pH, fertility and drainage need to
be carefully checked and maintained or corrected where necessary. Chemical and
physical maintenance programmes need to be adhered to, with problems identified
and resolved quickly.
What replaces triazines?
Now that atrazine and simazine are no longer approved
for non-agricultural use, managers have been forced to seek alternatives. It is
already well documented that the users of pesticides most commonly rely on
pesticide suppliers for advice on which products should be used. These agents
will clearly be keen to sell their own products and will be less keen to point
out the shortcomings of those products.
However, as Brian Cooper of ADAS emphasised, it is not only
the properties of a herbicide which determine its efficacy, but also the timing
of application; surface, terrain, and vegetation on which it is being applied;
the application rate; and whether it is mixed with other AIs.
The most commonly mentioned replacements for atrazine and
simazine are diuron where a residual herbicide is desired, and glyphosate where
a contact-translocated herbicide is preferred which has no residual properties.
Diuron has already been detected in drinking water sources and there are
concerns that if this problem is not solved it will soon be banned for the same
reasons the triazines were banned. Diuron formulation producers are being
pressed to recommend lower application rates, single annual applications, and to
prevent application on drain covers and open gulleys. The problems with
glyphosate are that complete weed control needs more than one annual application
which becomes expensive; and weeds need to be relatively large in order to
attain effective control which leads to a public perception that there are more
weeds present.
Other herbicide active ingredients are available but tend to
be less frequently used for a variety of reasons, the most common of which is
lack of information. Paraquat is often rejected because of its high toxicity,
and imazapyr because of its effects on trees, but dozens of other products are
rarely used and some are even disappearing from the marketplace because of lack
of interest. The reliance on so few active ingredients is not only likely
to lead to problems of target resistance, but may repeat or exacerbate problems
of the kind which led to the triazine ban.
Other topics covered at the conference
included pesticides legislation, mammalian pests, economic aspects and the use
of agrobiologicals in amenity situations. (MD)
Proceedings from the conference will be
available from the National Turfgrass Council (NTC), 3 Ferrands Park Way,
Harden, Bingley, W. Yorks., BD16 1HZ, Tel: 0535 273188.
[This article first appeared in Pesticides News No. 23, March 1994, page 16]