DEVELOPING HYDROGEL® FOR SELECTIVE MANAGEMENT OF SUBMERGED AQUATIC WEEDS

A new technique for applying the aquatic herbicide - diquat for the control of submerged aquatics was developed in New Zealand and is now being used widely in both New Zealand and Australia. This method involves the use of guar gum, and formulating a diquat gel form (Hydrogel®), which can then be applied to water as a surface spray. The gel droplets sink rapidly on to submerged plant beds, releasing diquat at in the vicinity of target plants. This allows cost-effective ‘spot treatments’, targeting both containment of large infestations of an undesirable species, and eradication of small patches. Several case studies from Australia are discussed, in which diquat, used with Hydrogel®, provided cost-effective control of large infestations of submerged aquatics – hornwort (Ceratophyllum demersum), Egeria (Egeria densa), sago pondweed (Potamogeton pectinasus) and naiads (Najas tenuifolia and Najas marina) in urban wetlands, large and small lakes and a river. Recent trials in shallow ponds indicate that dense infestations Hydrilla (Hydrilla verticillata) infestations could also be reduced by approximately 50-70% with one or two treatments. However, in deeper and larger lakes, hydrilla control has been variable. In addition, Hydrogel® provides excellent control of filamentous green algal scum and submerged beds of Charophytes – Chara and Nitella at nominal costs. Results indicate that diquat residues rapidly dissipate from treated waterbodies after Hydrogel® treatments. The advantages of using Hydrogel® include reduced herbicide loads, savings in cost, increased confidence in treatment outcomes, and reduced risks of undesirable impacts on non-target species and aquatic ecosystems.