Septoria cannabis (yellow leaf spot)

Small lesions (yellow, ochre, white or grey-brown) first appear on the lower leaves in early June. The spots may remain small and round but usually enlarge into an irregular polygon shape, which are partially delineated at the edges by leaf veins. Tiny pycnidia arise within the spots on the upper surface of the leaves, and not on the underside as reported by Flachs (1936). Eventually, the leaf spots dry out and fragment, leaving a ragged 'shot-hole' effect in the leaves. In severe infections the leaves curl, wither and drop prematurely, resulting in defoliation of the lower part of the plant (McCurry and Hicks, 1925; Ferraris, 1935; Watanabe and Takesawa, 1936; Barloy and Pelhate, 1962; Ghani et al., 1978). Kirchner and Boltshauser (1898) illustrated yellow leaf spot in a classic lithograph, from which many subsequent illustrations are copied (Flachs, 1936; Ceapoiu, 1958; Barloy and Pelhate, 1962).Although yellow leaf spot principally affects the lower leaves, it may also arise in the upper leaves during flowering (McPartland et al., 2000). Spots may also appear on the stems (Gitman and Boytchencko, 1934; Ferri, 1959; Ondrej, 1991) and the seedling cotyledons (Ferri, 1959).

Minor infestations of yellow leaf spot will reduce yield of fibre, flowers and seeds. Severe epidemics, however, may occasionally cause catastrophic losses. In severe infections, the leaves wither and drop prematurely, resulting in defoliation of the plants (McCurry and Hicks, 1925; Ferraris, 1935; Watanabe and Takesawa, 1936; Barloy and Pelhate, 1962; Ghani et al., 1978).Quantitative estimations of crop losses do not appear in the literature, but crop damage has been reported in Italy (Ferraris, 1935) and Pakistan (Ghani et al., 1978).