Pollinating highbush blueberries Rufus Isaacs Department of Entomology, Michigan State University

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1 Pollinating highbush blueberries Rufus Isaacs Department of Entomology, Michigan State University

2 Resources Michigan Pollinator Initiative Integrated Crop Pollination The Pollinator Partnership

3 Blueberry pollination experiences. How can you decrease the risk of poor pollination?

4 Patricio Brevis

5 Patricio Brevis

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7 Patricio Brevis

8 Patricio Brevis

9 No bees Bees

10 Avg. wt (g) per berry More fertilized seeds = larger Jersey berries Mature Jersey, stocked with honey bees R 2 = Mature seeds per berry

11 Recommended colony stocking densities Cultivar Strong honey bee colonies / acre Rubel, Rancocas 0.5 Weymouth, Bluetta, Blueray, Pemberton, Darrow 1.0 Bluecrop 1.5 Elliot, Coville, Berkeley, Stanley 2.0 Jersey, Earliblue 2.5 Source: NRAES-55 Cooperative Extension Bulletin (1992). Oregon State University recommends 3 colonies per acre Some Michigan growers use up to 6 colonies per acre, for lower risk of poor pollination

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14 3/1 3/11 3/21 3/31 4/10 4/20 4/30 5/10 5/20 5/30 6/9 6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28 9/7 9/17 9/27 10/7 10/17 10/27 GDD - base 50 F Degree day accumulations Fennville Enviroweather station

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16 5/1 5/5 5/9 5/13 5/17 5/21 5/25 5/29 6/2 6/6 6/10 6/14 6/18 6/22 6/26 6/30 5/1 5/5 5/9 5/13 5/17 5/21 5/25 5/29 6/2 6/6 6/10 6/14 6/18 6/22 6/26 6/30 Air temperature ( o F) Extreme heat on Memorial Day weekend, Grand Junction West Olive o Average highs = 75.4 o F Average lows = 55.8 o F 17 hours over 90 o F in May Average highs = 76.3 o F Average lows = 55.7 o F 13 hours over 90 o F in May

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18 Extreme heat can affect many aspects of pollination Flower development 2006 study on sorghum pollen produced Pollen production Pollen viability pollen viability Pollen germination pollen germination (and fertilization?) Temperature (F)

19 Fruit damage (% of yield) Temperature ( o C) Misting to cool flowers Misting system applied 15 minutes every hour to cool berries. Temperature reduced o F below air temperature. Cooling reduced fruit damage and increased harvestable yields. Oregon State University Yang and Bryla (2018)

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21 Nectar remaining in flowers indicates low bee visitation

22 More bees = larger Bluecrop berries Bee abundance affects berry weight Each point is a Michigan or British Columbia farm in one year > 25 bees per 10 min on 10 bushes There are three and two years of data included, respectively Spearman s rank correlation: S =38259, p < , r = 0.61 Michigan British Columbia < 10 bees per 10 min on 10 bushes

23 Sampling bee activity Measure to make sure you have sufficient bees for pollination. Fields can be sampled a few times during bloom. Are you way below, just right, or way above the number for full pollination? 2018 pilot study in Bluecrop 10 minute samples on 10 bushes Count bees.

24 Average bees per 10 minutes Bluecrop fields 2018 bee activity samples above 25 bee threshold 7 well below 3 intermediate

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26 Use strong honey bee colonies Best pollination if colonies are strong. OR/WA standard for Grade A Orchard colony: Six frames of comb well covered with bees 3000 sq inches of comb 600 sq inches of brood 10 pounds of honey, or equivalent normal laying queen Contracts can be used to describe number and strength of colonies. A proposal: Growers pay beekeepers for strong colonies. Not weak ones. Beekeepers get paid well for their colonies.

27 Integrated Pollinator Management Stock fields with optimal number of strong colonies. Measure to make sure you have sufficient bees for pollination. Fields can be sampled a few times during bloom. Are you way below, just right, or way above the number for full pollination? Help maintain bee health through good farm management.

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31 Bees with access to diverse pollen & nectar sources Live longer Have greater reproduction Have lower pathogen infection Can resist pesticides better

32 % bloom Research needs. Improved prediction of bloom Aurora Bluecrop Duke Elliott Jersey Liberty Cumulative GDD Understanding high temperature effects Temperature reduction strategies

33 Take home messages Pollination is a critical phase of blueberry development. Stock fields with strong honey bee colonies. Check them! Monitor crop pollination, and learn from experience. Consider misting (or overhead irrigation?) for cooling. Support wild bees too, to help guarantee pollination.