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SUMMARYPests and diseases cause appreciable loss to tea in north-east India, but their incidence and intensity of attack vary widely from district to district, and within districts with variation in climate, elevation and the jat (seed-source) of tea. For example, blister blight is a serious disease in Darjeeling and looper catepillar is mainly localized in certain tea estates of the Assam valley. Thus recommendations regarding pesticides and their application in a particular region must be based on a thorough knowledge of the distribution of the diseases or pests in the region. This can best be obtained through sample surveys, planned in representative estates of the region and carried out with the help of trained investigators. Such surveys will also provide basic data on jat, environment and disease, as a guide to experimentation.

Crinkle-leaf is an abnormal condition of the leaf of coffee in Kenya, the cause of which is unknown. Preliminary observations showed that its symptoms are suppressed by spraying with captan and experiments were carried out to investigate whether this material would provide an economic coi jjtrol. Spraying at the rate of 4 lb per acre, when symptoms of the condition first appeared, gave good control but lower quantities were less effective. Means of predicting the severity of the condition have not yet been evolved and the spray programme must therefore be adjusted each season to meet the local conditions. The spraying of nurseries and young suckers is recommended as soon as early symptoms are noted, since the cost is low, whereas the spraying of large areas of mature coffee requires a careful assessment of the possible economic advantages. Susceptibility to (B-inkle-leaf was found to differ between cultivars.

Estimates of the loss of tea crop due to red spider mite have been derived using three different methods: (1) least squares, (2) Wald's method, and (3) Bartlett's method, for the case when the relationship between yield and infestation is linear. The results have been illustrated with the help of data collected from sample surveys on pests and diseases of the crop conducted in the Dooars, a region of north-east India.