By: Sherri Roberts AAg, Regional Crops Specialist (Weyburn)
While most producers are aware that aster yellows can infect canola, many are unaware of its ability to infect other crops. In a 2007 survey done in Saskatchewan, the average aster yellows incidence (the percentage of plants with symptoms of the disease) reached 11.2 per cent in canola, 66.6 per cent in barley, 38.8 per cent in wheat and 25.4 per cent in oats. Additional hosts that are susceptible to aster yellows include camelina, flax, herbs and spices, pea, chickpea, sunflower, alfalfa, and bromegrass.
Infections occur when the phytoplasma that causes the disease is spread from one plant to another by an insect vector. The most common insect vector of aster yellows in Saskatchewan is the leaf hopper. While leafhoppers generally come into Canada on southerly winds from the United States, it is suspected that aster leafhoppers may be able to over-winter as adults, especially if the winter is mild and there is reasonable snow cover.
Leafhoppers possess piercing sucking mouthparts. As they puncture leaf blades to suck out the natural juices, they inject the aster yellows phytoplasma. Aster yellows symptoms in wheat include spotting (white specks), yellowing, leaf curling, stunting and distortion of plants. These symptoms become more pronounced in later growth stages, such as at heading.
Leaf hopper damage is being found in winter wheat fields in the Southeastern part of the Province. Field sweeps are being conducted but there are no thresholds established for aster yellows nor are all leafhoppers infected. Additional information in regards to aster yellows can be found in our Aster Yellows Factsheet.