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Get ready for the 2011 Battle of SWD pestmanagement


Four-pronged strategy needs full participation to help deal with increasing infestation by insect pest.


By Mark Sweeney and Tracy Hueppelsheuser


T


he 2010 growing season was our first full-year experience with Spotted Wing Drosophila (SWD) and what a year it was! Pest pressure was beyond our worst-case scenario. Growers who did not do an adequate job of protecting their crops learned a hard lesson. While all berry crops (except cranberries) are good hosts, at greatest risk were raspberries, blackberries and blueberries that matured after the middle of July when fly trap counts exploded.


In spite of considerable research efforts throughout the western fruit growing regions, much is yet to be learned about the behaviour of this pest. Some of what we are learning is cause for concern. Adult flies are very hardy—they were trapped all through the winter and early spring in spite of several spells of temperatures below -10 C. This, along with the fact the 2011 season ended with trap counts over 100 times higher than in 2010, may mean that pest pressure may arrive earlier and be even more severe that last year.


In order to win this war and maintain our reputation as growers of high-quality fruit, a concerted area-wide management program will be necessary in 2011. There are four components to a SWD management plan. All growers need to participate.


MONITORING


Widespread field monitoring will be continued in 2011. Results will be reported through the Blueberry IPM Newsletter, the Small Fruit Update and will be posted at www.al.gov.bc.ca/cropprot/swd_trapresults.pdf. Growers are also encouraged to work with their consultants and/or field reps to trap in their own fields. Once SWD adults are detected on your farm or within your area and ripe fruit is present, a spray program should be begun to protect the crop through to the end of harvest.


SANITATION


SWD adults are particularly attracted to over-ripe and rotten fruit. California raspberry growers have found that careful removal and disposal of cull fruit has reduced pest pressure. On hand-harvested farm, this may be feasible and is certainly advisable. However, in large-scale mechanically harvested crops there may be no really practical way to dispose of dropped fruit.


ALTERNATEHOSTS


SWD has an amazingly wide host range. In the Fraser Valley there are many crops and non-crop plants that can provide breeding and feeding sites. Early fruiting plants such as Indian plum, salmon berry and seedling cherries are a concern. This early fruit likely provides a site for the


10 British Columbia Berry Grower • Summer 2011 Hueppelsheuser Sweeney


overwintering generation to feed and reproduce before crops begin to ripen. Late fruiting plants such as Himalayan and evergreen blackberries provide food and breeding sites from July through November. In addition, blackberries are believed to be a key overwintering site. It is not feasible or desirable to eradicate these plants. However, growers should try to control these alternate hosts in areas immediately adjacent to fields. They can be mowed or treated with herbicides so that they do not fruit. Herbicides should not be applied near watercourses.


PESTICIDES


Insecticide sprays are the key weapon against SWD. In 2010, emergency registrations of four products were obtained: Ripcord, Malathion, Delegate and Entrust (for organic fields). Based on


research trials and field experience, these products are known to be effective in preventing fruit infestation. Sprays are applied when flies are detected and when ripe fruit is present. Adult flies are the target — flies are killed by direct spray and by being exposed to spray residues on leaves and fruit. It is important to get spray penetration through the canopy as flies are known to prefer shady areas. Flies can rapidly re-infest fields from outside, so spray protection through the harvest period on 7-14 day intervals is required. Rotation of products is essential to prevent pest resistance. A post-harvest spray should be applied to fields adjacent to later crops as the remaining fruit can act as SWD breeding sites.


Strawberries and raspberries are relatively easy to spray with conventional equipment. However, mature blueberries are a major challenge as the heavy canopy makes it difficult to access the field without causing significant crop damage. Creative approaches are required. Larger growers are investing in high-clearance field sprayers capable of straddling a row and covering up to 10 rows at a pass.


Custom sprayers are another option. There is some capacity in the Fraser Valley which could be expanded. For smaller growers, small air-blast sprayers with small, narrow- profile shielded tractors or even ATVs may work to allow access with minimal crop damage. Some growers are using cannon sprayers, but there are concerns with obtaining adequate coverage and controlling drift. Helicopter spraying is being used in the US, but coverage is a concern and aerial will not likely be an option in the Fraser Valley. For ground spraying, better pruning and training is required to keep fruiting area upright to allow improved field access. For 2011, emergency registrations are again being sought. Further information will be available soon and posted at: www.agf.gov.bc.ca/cropprot/swd_management.pdf. — Mark Sweeney is the berry industry specialist and Tracy Hueppelsheuser an entomologist with the BC Ministry of Agriculture, Abbotsford.


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