Yield reduction caused by Phaeosphaeria nodorum leaf spots at different spring wheat growth stages

Greenhouse studies were carried out to evaluate the effects of foliar leaf spots caused by P. nodorum on spring wheat (Triticum aestivum, cv. Laval 19 ) yield. Wheat plants were inoculated at booting, heading, flowering and mi lking growth stages. Experiments were first performed in winter 1993 and re peated in winter 1994. Inoculation of P. nodorum usually resulted in an inc rease of leaf spots and a decrease of yield compared to uninoculated plants . Foliar flag leaves spots were similar to total plant foliar leaf spots. A ll variables were significantly affected by inoculation stages infected fol iar area, biomass of straw and leaves, biomass of spikes, biomass of grains , vegetative biomass and harvest index. Inoculation at milking growth stage seemed to result in the least negative impacts on yield compared to all ot her stages. From the results of this study and observations performed in Qu ebec during the 15 past years, leaf spots caused by P. nodorum should not r esult in important spring wheat yield losses in Quebec.