2017 ASHS Annual Conference

Management of spotted wing drosophila (Drosophila suzukii, SWD) is difficult for small fruit growers and novel strategies are necessary. Manipulating within-crop habitat via canopy and floor management could reduce its favorability for SWD while maintaining high marketable yields. In 2016 the University of Minnesota (MN), Maryland (MD) and Oregon State University (OR) collaborated to determine best pruning and mulching practices for SWD control in northern highbush blueberry (Vaccinium corymbosum) and primocane fruiting raspberry (Rubus idaeus). The pruning trial was conducted at all 3 sites, with raspberry being studied in MD and blueberry being studied in MN and OR. Pruning treatments included the grower standard at each site, a light prune (≈25% more canopy) and a heavy prune (≈25% less canopy). Within each treatment we measured marketable yield, fruit SWD infestation, and canopy/berry temperatures. The mulching trial featured 3 treatments: black landscape fabric and wood/sawdust mulch, with treatments above and within the mulch layer. We artificially infested fruit, followed by bagging and placement into field treatments. SWD eggs in each berry were counted before being bagged, and adult emergence was calculated after the field trial concluded. Temperatures within each treatment were recorded as well. Results for the pruning trial were variable by location. Pruning treatment only had an infestation effect in MD raspberries, where SWD infestation was highest in the light prune treatment. MD raspberries and MN blueberries had higher marketable yields and lower temperatures in light prune treatments, while we observed no differences by treatment in OR blueberries. Mulching trial results were more consistent among sites. In OR, MD and MN, average maximum temperatures were lower in the within-mulch treatment than above-mulch and landscape fabric treatments. Correspondingly, the within-mulch treatment had higher rates of SWD development and emergence. Based on 2016 data, pruning and mulching recommendations for SWD control in raspberry and blueberry is mixed. Heavier pruning often leads to higher maximum canopy temperatures, which may be correlated with lower SWD infestation in some areas. However this effect alone is likely not enough to justify an associated reduction in total marketable yield. For mulching, SWD larvae appear intolerant of the high maximum temperatures on black landscape fabric or the top of wood and sawdust mulches. Thus we recommend against the common practice burying fallen fruit for sanitation, as this provides an insulated environment that SWD eggs, larvae and pupae prefer.