Technical


Water can be one of the most valuable landscape features on golf courses and in parks, with aesthetic and environmental value, adding to leisure opportunities or providing a valuable source for irrigation. Streams, ponds and lakes also offer inviting growing conditions for a range of vegetation, some welcome and some not.


Control of aquatic (in water) and riparian (adjacent to water) vegetation presents some additional challenges as the use of herbicide products for aquatic use is tightly controlled


A


above the water surface, the maximum area of emerged leaf and at around the time of flowering, such as this Himalayan Balsam


Plants are likely to be susceptible to herbicide treatment if they have a substantial part of their foliage exposed


quatic use is defined as spraying in or on land immediately adjacent to a body of water, where the land immediately adjacent to is designated as the bank of the body


of water. The body of water can be enclosed, i.e. ponds or reservoirs which do not drain to a watercourse, or open, i.e. rivers, streams and ditches which drain to a watercourse. Aquatic weed control specialist Dr Jonathan Newman of Waterland Management Ltd comments: “Riparian weeds can prevent access to water bodies, and submerged weeds can restrict leisure activities such as fishing or sailing, by clogging up the water. Emergent riparian weeds (usually reeds and rushes) can encroach into the lake or across a line of sight.” “Non-selective herbicides must only be used on those weeds that you need to control, and not used as a broad treatment, as they will usually kill most green vegetation, so applications need to be carefully planned.”


Choose your weapon


Traditional cutting is often used to control aquatic and riparian weeds, but often fails to eradicate the problem, just delaying it for a while, suggests Dr Newman. “Tackling submerged weeds by using dyes


from early spring works best, and selective application at the right time of year of approved glyphosate products controls emergent weeds and aquatic weeds with floating leaves.”


He adds that weed cutting boats and


harvesters are always available for crisis management, but the problem will usually come back next year. “Effective herbicide treatment usually gives


significantly longer control of up to five years, and costs much less than mechanical control.” Roundup ProActive and Roundup ProVantage


can be used to control emergent and floating aquatic weeds in ponds, reservoirs, rivers, ditches, drainage channels and riparian situations. When used as directed, there is little risk to spray operators, wildlife or the environment and they may be safely used in waters stocked with fish. When used as recommended, any water


subjected to glyphosate may be used immediately for irrigation. The best method of dealing with emergent


riparian weeds is to spray with aquatic approved formulations of glyphosate from late August onwards, Dr Newman comments. “Earlier applications will kill the emergent


weeds, but they will regrow in the following year. Later applications tend to kill the roots and rhizomes much more effectively, preventing any regrowth.” “Submerged weeds are much more difficult


to deal with now, as there are no currently approved herbicides for use on them.” Weeds with floating leaves, such as water


lilies and some pond weed species, can be treated from about June onwards, at a slightly higher application rate than that used for


PC AUGUST/SEPTEMBER 2017 I 143


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