YELLOW CANOPY SYNDROME: A CONDITION OF UNKNOWN CAUSE AFFECTING SUGARCANE CROPS IN QUEENSLAND

YELLOW CANOPY SYNDROME (YCS) is a condition that was first recognised in early 2012 in the Smithfield area near Cairns but has since been observed extensively from the Mackay area north. Crops in the wet tropics (Tully-Babinda) are the exception and suffer considerably less from the condition; very few yellow crops caused by YCS have been reported in this area. The condition is characterised by yellowing of the leaf canopy and the cause remains unknown. Symptoms may appear at regular intervals during the growing season but equally may be seen only for a brief period in a particular crop. Crop stress may be linked with symptom appearance; the most severe symptoms seem to occur when the crop begins to form mature stalk material, though this is not always the case. Yellow leaves quickly senesce and canopy recovery occurs with the production of new green leaves. It has been difficult to quantify yield losses as identification of YCS-free crops is not possible, given the variable symptom expression, the lack of a reliable assay and unreliable onset of crop effects. Some evidence points to losses of up to 30% in specific crops; losses appear to be related to lower photosynthetic rates in affected leaves.