THE EFFECT OF DOWNY MILDEW ON SUGARCANE YIELD IN THE VARIETY B72177 AT RAMU SUGAR, GUSAP, PAPUA NEW GUINEA

B72177 is a major commercial cultivar for Ramu Sugar Limited, grown on 20% of the total area. Studies were carried out on the effect of downy mildew on the yield of this variety, through the planting of varying proportions of healthy and diseased cane in a range of field plots. Higher infestations of downy mildew reduced cane yield parameters. Thirty-three per cent loss in cane yields and 45% loss in tonnes sugar were observed for 60% observed downy mildew disease levels. Further reductions in yields of up to 58% tonnes cane and 75% tonnes sugar were observed for 100% observed disease. These results show that downy mildew is a disease of serious economic importance.