SWD: Lessons learned in 2013
Growers advised to heed area-widemonitoring reports, spray early and maintain a tight interval between applications leading up to harvest.
By Tamara Leigh T
he 2013 growing season was the worst on record for Spotted Winged Drosophila (SWD) infection in British Columbia. The pest has been present in the province’s fields and orchards since 2010, and with time and the concerted effort of researchers, growers and consultants, the industry is slowly getting a more complete picture for managing and predicting SWD risk. Provincial entomologist, Tracy Huppelheuser, shared lessons learned from the 2013 season at the Horticulture Short Course in January, particularly in monitoring and spray intervals.
Instead of a focus on trapping in individual fields, the monitoring program undertook an area-wide survey around Abbotsford and Langley. The survey placed Contech traps baited with apple cider vinegar in 10 commercial raspberry fields, with two edge traps and two middle traps in each field. Trapping began on June 6, and continued until August 30.
“We have found that in-field trapping is not a good indicator of SWD risk,” says Huppelheuser. “Area-wide trapping surveys give a better overall view of regional fly numbers.” In addition to trapping, fruit collection began in June. Samples taken from raspberry fields on June 20 showed no larvae were present when they were floated out in a saltwater solution, but flies were present when the fruit was incubated. By June 24, collection and floats of collected fruit resulted in positive SWD. Based on this early presence, Huppelheuser recommends that growers start spraying early, around the third week of June, to prevent SWD from getting established in the fields. The summer of 2013 was also the first year of a study to determine optimal
16 British Columbia Berry Grower • Summer 2014
spray intervals. Four conventional, machine- pick raspberry fields in south Abbotsford were used in the study, all with confirmed SWD. Three fields were
treated at different spray intervals during harvest – 5-6 days, 6-7 days and 13 days between treatments. Results clearly showed that shorter spray intervals, less than seven days, gives better control of SWD. Overall, when it comes to SWD management, Huppelheuser suggests growers pay attention to area-wide monitoring reports, spray early and maintain a tight interval between applications leading up to harvest. These practices, combined with proper sanitation in the fields, short picking intervals and good fruit handling practices, will help keep the populations of SWD in check.
areas until January. In 2013, early warm weather meant SWD over-wintering females were out and active early, laying their first eggs in May.
KAITLYN SCHURMAN, AAFC
Researchers at Oregon State University have developed a Degree Day Model that can help predict how fast SWD will develop based on accumulated heat over a
threshold temperature. The model can create a table of life events like emergence and egg laying for subsequent generations of SWD based on local temperatures.
“The field data and degree day models match, so we should be able to use the models in the future to help make pest management decisions,” says Huppelheuser.
The B.C. Ministry of Agriculture is maintaining area-wide SWD monitoring year-round, providing an increasingly clear picture of the lifecycle of the flies, as well as the relationship between temperature and SWD populations. Winter monitoring, done in the hedgerows between fields, has found that numbers can stay high in these
Information generated by the Degree Day Model will be integrated into weekly SWD reports put out by the Ministry of Agriculture. Huppelheuser reminds growers to watch for updates and new information throughout the season through the B.C. Blueberry Council newsletter and the provincial website for updates on SWD (www.agf.gov.bc.ca/cropprot/swd.htm
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