Summary.Three cucumber mosaic diseases of this country and the causal viruses are described.The first disease, green‐mottle mosaic (cucumber virus3), and the second, yellow mosaic (cucumber virus4), are not transmissible to solanaceous plants.Cucumber virus3, on cucumber, causes a dark green mottle with blistering and distortion of the leaves, but the fruit is not usually marked; whilecucumber virus4 gives rise to a distinct type of leaf‐mottle, yellow to silver‐white in colour, and the fruit may be seriously marked. The third disease, yellow‐mottle mosaic (cucumber virus1), is characterised by a diffuse yellow mottle of cucumber leaves and fruit and is transmissible to solanaceous plants. Cucumber viruses 3 and 4 are described for the first time.Notes are given on fern leaf of tomato, insect vectors and control m