Aster yellows: No evidence of a problem in 2013

June 19, 2013 - Issue 12

Aster leafhopper numbers are quite low so far this year, down considerably from 2012. Aster leafhoppers carry aster yellows phytoplasma, so without leafhoppers to transfer the disease, there is no infection. Based on what we know at this stage, there is no evidence of a significant aster yellows risk for 2013.

South winds that carry aster leafhoppers from the southern U.S. arrived more than a month later in 2013 than in 2012. This is a factor in lower numbers this year. In 2012, North Dakota and Minnesota entomologist noticed high leafhopper numbers early on and alerted Western Canada entomologists of a potential outbreak. North Dakota and Minnesota have not issued sentinel warnings for 2013. The long winter of 2012-13 may have been another factor in reducing any chance of winter survival of leafhoppers on the Prairies. The winter of 2011-12 was unseasonably mild.

Late infestations are still possible, but the indication so far is that aster yellows will not be a major issue in 2013.

Not enough leafhoppers to warrant an insecticide spray. A single spray is rarely economically effective anyway — even when leafhopper numbers are high. That’s because (1) the leafhoppers can come in waves, (2) usually only a low percentage of leafhoppers carry the phytoplasma, and (3) canola is not a preferred host crop for aster leafhoppers, even though they will feed on it. Anecdotally, it seems that some fields may have benefitted from insecticide spray last year, but we do not know for certain what timing was most effective and whether this can be replicated. Many fields sprayed for other insects around the same time last year still had high levels of aster yellows. So whether a single application could potentially lead to any significant reduction in aster yellows in years when high levels and heavily infected populations blow in early is not fully known. Consistent reduction in levels of aster yellows from a single application is doubtful from what we know of aster leafhopper and its management on other crops.

AAFC testing samples. AAFC is screening plants and leafhoppers for aster yellows phytoplasma. If you find any plant with odd growth patterns, AAFC could test it for you. Some dandelions in Alberta were found this month with what looked like aster yellows. Plants can be sent dried or fresh between pages of newspaper to absorb humidity, and placed in a cardboard box to avoid crushing. Express shipping is best to avoid rotting.
Leafhoppers can be sent alive or frozen. Living specimens should be placed in a small vial with a few grass leaves and sent by courier or priority mail. They can survive 2-3 days with leaves to feed on. Frozen specimens should be placed in a vial and sent with a cooler pack with dry ice or ice by courier to avoid thawing. No test can be run on thawed leafhoppers as the DNA will be degraded. Specimens can also be placed in vials containing ethanol 70%. The vials should be tightly sealed, placed in a cardboard box and sent by regular mail. Ship to: Chrystel Olivier, AAFC, 107 Science Place, S7N0X2, Saskatoon, Saskatchewan, 306-956-7686.

Canola Watch