Studies on five potential botanicals locally known as Kimbinga, Mnyaa, Mwarobaini, Lipangati, Kibamba against cashew powdery mildew disease caused by the fungus Oidium anacardii were conducted in the field and in vitro during the 2012/2013 cashew season. The aim of this study was to investigate the performance of botanicals against cashew powdery mildew disease in Tanzania. Field studies were carried out on six cashew trees selected from a vegetatively propagated cashew block established in 1989 at Naliendele Agricultural Research Institute, Mtwara, Tanzania. Ten shoots were tagged on each tree. Each potential botanical plant tested including control was assigned to one tree. Extracts from these botanical plants were prepared once a week from 24th July to 16th September 2012 and sprayed on flower panicles of the previously tagged shoots on the respective trees. followed by mildew assessment estimated using the 0 – 6 disease severity key. Besides, in vitro studies were conducted in a pathology laboratory at the same institute at the end of the cashew season. The final field disease assessment showed that panicles sprayed with Mwarobaini extracts had the least mildew infection level (31.5%), followed by Kibamba (35.5%), Mnyaa (36.5%) and Lipingati (41.8). Kimbinga plant extracts attained the highest mildew infection (80.8%) which was close to the 100% level recorded on the control flower panicles. In vitro studies revealed that all tested plant extracts had significantly reduced the growth and development of the mildew disease. These preliminary results clearly indicate that the five botanicals Mwarobaini, Kibamba, Mnyaa and Lipangati appear to have some potential in controlling powdery mildew disease on cashew.

Keywords: powdery mildew; plant extracts; cashew