SMUT ESCALATION AND ASSOCIATED YIELD LOSSES IN A MACKAY VARIETY TRIAL

SUGARCANE SMUT HAS been of serious concern to the Australian sugarcane industry. Varietal resistance has offered a successful management strategy for the disease and data presented here clearly show how rapidly the disease may escalate in highly susceptible canes. Grassy stool development occurred under natural spread conditions within 18 months from planting in the highly susceptible Q157 in the Mackay district. Crop yield data in a variety trial showed that by third ratoon, yield in the highly susceptible variety Q157 plummeted to <40% of plant crop yield. Most other varieties remained largely unaffected by smut, even though in cases up to 20% of stools exhibited some form of the disease. Some susceptible (but not highly susceptible) varieties, such as Q138, continue to yield quite well even in the presence of low levels of smut. This is because disease severity does not escalate as in the highly susceptible varieties. This particular variety could remain commercially viable in the Mackay district if new crops are established without primary disease. Quantification of smut severity in crops of commercial varieties is predictive of commercial yield.