If you’re seeing malformed, flattened (bladdered) pods, aborted flowers or pods, or red, abnormally tall plants, your canola likely has Aster Yellows.
Aster Yellows, is caused by the transmission of a bacteria (called phytoplasma) to plants through the feeding action of an infected Aster Leafhopper called Macrosteles quadrilineatus. (There are numerous other species of leafhoppers on the Prairies, but they contribute very little to disease transmission). Most of the Aster Leafhopper population is migratory, arriving in the Prairies with air currents from Southeastern and Central United States from mid-May to July. Aster Leafhoppers are a particular problem after a mild winter caused by strong winds from the Southern United States, however experts expect a local population of leafhoppers may also overwinter on the Prairies. The migratory population is already infected with the Aster Yellows phytoplasma, which is widespread in the Southern U.S.
Once infected, leafhoppers remain infected for the duration of their life; usually 60 to 120- days, depending on weather conditions, food sources, and health of the insect population.
Conditions conducive for Aster Yellows development in canola include:
- Lots of leafhoppers with a high percentage of infection
- Strong and frequent winds originating in Southern and Central U.S.
- Weedy fields, which provide food and shelter for leafhoppers
Unfortunately, there are no fungicide control options for this disease, and spraying to control leaf hoppers is ineffective because they continue to arrive on winds from the U.S. for several weeks, and are able to move from field to field. Although the phytoplasma infection causes misshapen pods and flower buds and the infection looks awful and stands out, it rarely causes economical loss. Conversely, plants infected with aster yellows can have misshapen seeds and yield loss without showing any of the obvious signs of infection — such as the puffed bladder-like pods. The plant looks normal but some pods are empty or contain misshapen seeds.i
Experts suggest for a field with 1% plant infection, you can expect production loss ranging from 0.3 to 0.7%. In a field with 5% infestation, production loss ranges from 1.5 to 3.5%. It is uncommon to find a field with more than 5% infestation.
Differences between hybrids or herbicide tolerant canola systems have not been proven. Variance in disease incidence and severity between fields is more likely due to other factors, such as overwintering conditions, than to hybrid or system differences.
Wind trajectories and environmental factors are the big key factors in aster yellows development. If you see some malformed pods and red or purple plants in your canola fields this summer, your diagnosis of aster yellows is likely correct. Consult your DEKALB® agronomist if you require assistance with any of your diagnoses.
Canola Watch. (2012). Lots of Aster Yellows. (verified: June 5, 2014). Whitney Cranshaw, Colorado Sate University. Bugwood.org Retrieved From http://www.canolawatch.org