Overcoming powdery mildew in cashew

Tanzania was the world's second biggest producer of cashew nuts in the mid-1970s, but production plummeted during the late 70s and early 80s. By the late 80s production was only a tenth of what it had been at its peak. Investigation during this period by Italian and Tanzanian scientists showed that a new disease, powdery mildew caused by Oidium anacardii, was a major cause of the reduced yields. The disease affected blossoms and prevented fruit set. A subsequent pilot programme funded by the World Bank showed that application of sulphur dust could control the disease and increase tree yields up to 10-fold. However, chemical application is not an option best suited to resource-poor farmers or to the environment. In a major research programme funded by the UK Overseas Development Administration (ODA), emphasis was placed on the selection and use of disease resistant cashew plants. Some disease tolerant material has been identiffed and is being multiplied and distributed to farmers. Production of disease resistant material however, is a long-term process and outputs for the breeding programme will not be readily available for farmers' use for several years. Meanwhile, research by the ODA team has enabled improved disease control methods to be applied, based on knowledge of the biology of the disease and agronomic practices to rehabilitate cashew orchards. Dr J M Waller, CAB International Intemational Mycological Institute Bakeham Lane, Englefield Green Egham, Surrey TW20 9TY, UKTanzania was the world's second biggest producer of cashew nuts in the mid-1970s, but production plummeted during the late 70s and early 80s. By the late 80s production was only a tenth of what it had been at its peak. Investigation during this..