Influence of crop management on sunflower stem canker (Diaporthe helianthi)

Sunflower stem canker (phomopsis) is a fungal disease caused by Diaporthe helianthi Munt.-Cvet. et al. which is responsible for yield losses of up to 40%. A programme was carried out by INRA and Cetiom in Southwestern France (1994-2000) to analyze the effects of sunflower crop management on the frequency and severity of phomopsis. The proportion of stems infected by D. helianthi always increased with stem density while the effects of nitrogen supply were less clear-cut. Delayed sowing significantly reduced leaf and stem infection. Crop management systems were evaluated over 7 years: the reduction in plant density and N supply was not sufficient to lower the infection rate to the level given by fungicides, but in conjunction with delayed sowing, infection levels were comparable with early and protected sowings. Fungicide-free, low-input management was profitable provided that tolerant genotypes were used. Heavy rain in late spring limited the efficacy of cultural methods.