Stemphylium leaf spot (Lucerne Leaf Spot), caused by the fungus Stemphylium botryosum, is a common disease of lucerne which can cause defoliation when severe. This leaf spot often occurs in association with other foliar diseases. The leaf spots are oval or irregular, slightly sunken, and dark brown with lighter centres and surrounded by a pale yellow halo. Older spots may be concentrically ringed, resembling a target. A single lesion can cause a leaflet to yellow and fall. Stems can be blackened. The fungi are carried-over on infected plant debris (leaves and stems), seed and in the soil. Stemphylium leaf spot may develop under warm moist conditions and spores of these fungi are spread by wind and rain splash.