Optimizing Spray Coverage in Fall-Bearing Raspberries and Blackberries

Maggie Lewis and Kelly Hamby, Department of Entomology, University of Maryland

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In small fruit production, spray coverage can strongly impact pesticide efficacy; for example, increased spray coverage improves control of fruit rot fungi such as Gray mold (Botrytis cinerea).  Spray coverage may also be important when managing key insect pests, including spotted-wing drosophila (SWD).  In brambles, higher infestation and SWD adult activity occurs in the inner and lower plant canopy, regions that generally receive poorer spray coverage.  The dense foliage found in these fruit crops can block pesticide sprays, resulting in uneven deposition patterns that possibly create a refuge for SWD or other pests.  In this study, our primary objective was to improve spray coverage in raspberries and blackberries by optimizing carrier water volume and sprayer equipment.

Methods: Spray trials were conducted at Keedysville, MD from 2016 - 2017 using fall red-raspberries and in 2018 using fall blackberries.  Each year, fruit were sprayed using two carrier water volumes: 50 and 100 gallons per acre (GPA) with a Durand-Wayland 100 airblast sprayer; in 2018 we also attached a two-sided row crop head (DW 16-4935) to the airblast sprayer (Fig. 1) to better direct the pesticide spray.  We quantified percent spray coverage in the inner and outer canopy at three heights in raspberries and four heights in blackberries using white paper spray cards and Vision Pink Foam Marker Dye (GarrCo Products Inc.).

Results and Conclusions: In both 2016 and 2017, increasing spray volume consistently improved spray coverage in the outer canopy of raspberries (Fig. 2).  However, volume effects were less consistent in the inner canopy.  In 2016, we observed no difference in inner coverage rates between 50 and 100 GPA.  In contrast, inner canopy percent coverage in 2017 increased by 24% from 50 to 100 GPA.

 

The addition of a row crop head to the airblast sprayer in 2018 improved overall spray coverage rates in our single blackberry trial (Table 1).  With the row-crop head, we found no differences in coverage rates between the inner and outer canopy nor between the 50 GPA and 100 GPA applications (Table 1), suggesting that adjustments to the sprayer equipment may be sufficient for improving spray coverage.  However, further testing across a wider variety of sites is needed to verify these conclusions.  Bramble plantings with thicker canopies or other trellises may respond differently to carrier water volume treatments and sprayers.  We recommend checking spray coverage with water sensitive cards (if rain and dew will not interfere) or with a marker dye to identify and address issues to improve coverage.