ADDRESSING DEW PERIOD, THE MAIN CONSTRAINT TO SUCCESSFUL MYCOHERBICIDES
CF McRAE1,2 and BA AULD1,2
1CRC for Weed Management Systems, Australia;
Background and objectives
The real challenge, then, in mycoherbicide research and development is to overcome the dew period constraint. Formulation of the mycoherbicide can address this problem (and other handling, storage and application problems). With appropriate formulation it may be possible to deliver the fungus to the weed surface with sufficient water and to retain it for sufficient time to satisfy the dew period requirement of the fungus. The type of formulation varies with the method of application. For a soil-applied mycoherbicide, a granular formulation is most suitable, while a liquid-based formulation is the appropriate means of applying foliar mycoherbicides. In 1997, a project began at the NSW Agriculture's Agricultural Institute, Orange, to devise novel formulation systems for the delivery of pathogens as foliar mycoherbicides. The focus of the research is to find ways of reducing evaporation of the water sprayed onto plants at the time of inoculation and/or to find ways to retain that water on the plant surface for the dew period of the fungus under consideration. The model system for research is Colletotrichum orbiculare as the control agent of Xanthium spinosum. The techniques used by industries that deal in water-based products are under review for possible solutions to the problem. Further, the long-chain alcohols octadecanol and hexadecanol are being examined, because they have been shown to reduce evaporation of water under controlled conditions and have been considered as aids to reduce evaporation from farm dams in Australia .
Results and discussion
Both octadecanol and hexadecanol were trialled as aids to reduce evaporation from farm dams in Australia, but were finally abandoned mainly because of the large surface area of water and often windy surface conditions. In miniature these problems are less acute, and preliminary droplet studies have shown that crystal spread monolayers of both compounds slowed the evaporation of droplets containing C. orbiculare and Tween 80. Hexadecanol is being considered in plant trials. Mixtures of polymeric gels also show promise as water-retaining substances, particularly mixtures incorporating xanthan gum.