The effects of sowing date and nitrogen availability during vegetative stages on Leptosphaeria maculans development on winter oilseed rape

Phoma stem canker, caused by Leptosphaeria maculans (anamorph Phoma lingam), is one of the most serious diseases of oilseed rape world-wide. However, little is known about the effects of cultural practices on phoma stem canker development. We carried out a field experiment, in 2000/2001 and 2001/2002, at Grignon Experimental Unit (Paris Basin, France) to assess the effects of sowing date and nitrogen availability during vegetative stages on phoma stem canker development on two winter oilseed rape cultivars. We studied eight treatments corresponding to the combination of two sowing dates-early (beginning of August) and typical (beginning of September)-two levels of nitrogen availability during vegetative stages-application of 0 or 250 kg N ha(-1) before the end of autumn, subsequent spring nitrogen fertilizer application being adjusted according to the needs of the crop-and two cultivars-Bristol (susceptible to phoma stem canker) and Pollen (slightly susceptible). Early sowing resulted in smaller crown cankers, whereas high nitrogen availability during the vegetative stage favoured crown canker development. Significant interactions between cultivar susceptibility and cultural practices were observed in the second year of the experiment. Crown canker development was more strongly limited by early sowing for Pollen than for Bristol. Similarly, high nitrogen availability during the vegetative stage increased crown canker development more strongly for Pollen than for Bristol. The results presented here should facilitate integration of the risk of phoma stem canker development into the choice of the sowing date and nitrogen management within the cropping system. (C) 2004 Elsevier Ltd. All rights reserved.