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.

Figure 1. Airblast sprayer with a two-sided row crop head used in the 2018 blackberry trials.

Figure 2.  Mean percent spray coverage ± standard error observed at 50 and 100 GPA in the inner and outer plant canopy (averaged across heights) in the (A) 2016 and (B) 2017 raspberry spray trials. Asterisks indicate significant differences in coverage between 50 and 100 GPA at each canopy location.

Table 1.   Mean percent spray coverage ± standard error observed
 in in the inner and outer canopy of blackberries 2018 at four heights (approximate feet above ground).

Acknowledgements: Thanks to Bryan Butler, Galen Dively and Douglas Price for helping apply spray treatments at Keedysville, to Logan Miller, Alyssa Truong, and Nurani Illahi for helping process spray cards, and to our cooperating growers. Vision Pink Foam Marker Dye samples were provided by GarrCo Products Inc. (Converse, IN). Funding was provided by the Maryland State Horticultural Society and Maryland Department of Agriculture (171501-05). This publication was supported by the Specialty Crop Block Grant Program at the U.S. Department of Agriculture through grant. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.

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