STUDIES ON SPRAY DEPOSITION ON CASHEW TREES IN TANZANIA WITH REFERENCE TO THE USE OF FUNGICIDES TO CONTROL OIDIUM-ANACARDII

Water-based organic fungicides are being introduced into Tanzania as a n alternative to sulphur dust for the control of powdery mildew on cas hew trees, caused by the fungus Oidium anacardii. Spray application tr ials using motorised knapsack mistblowers were carried out to determin e the minimum volume of spray required to achieve acceptable canopy co verage. Further trials assessed the feasibility of using lever operate d knapsack sprayers with both commercially available and customised la nce assemblies. In both cases, spray distribution on the cashew tree c anopy was determined using a dye tracer with colorimetric analysis of foliage and image analysis of card spray targets. Application using th e motorised mistblower gave uneven canopy coverage with a typical esti mated application efficiency of 45%. Although it was possible to achie ve relatively good spray distribution over the cashew canopy and an ap plication efficiency of better than 50% using the knapsack sprayer and lance, the method resulted in unacceptably high levels of operator co ntamination. (C) 1997 Published by Elsevier Science Ltd.