OSU BLUEBERRY SCHOOL
March 16-17, 2015
held at
Oregon State University, Corvallis, Oregon
This two-day blueberry “school” was organized for new and experienced blueberry growers,
farm managers, crew leaders, advisors, packers/shippers, and consultants. Experts from Oregon
State University, USDA Agricultural Research Service, Washington State University, and the
blueberry industry were asked to address key issues of where the blueberry market is going; how
you might be more successful in tight labor or volume markets; which cultivars are easiest to
grow and are in most demand; how to establish new acreage using cutting-edge methods;
projected costs and the resources available to growers for selecting new planting sites; how to
best manage existing acreage to maximize returns of high-quality fruit; provide basic information
on blueberry plant physiology to help growers minimize environmental stresses and improve
yield potential; nutrient management programs for optimal growth and quality; irrigation and
fertigation practices for higher quality and better efficiency; use of organic amendments and
mulches; planning for and improving machine harvest efficiency; pruning for hand or machine
harvest (where can you cut corners….or not), maximizing pollination for good fruit and seed set;
overviews of the most important blueberry viruses, diseases, insects, weeds, and vertebrate pests;
and tools for good pest management. Information throughout the program addresses the needs of
conventional, transitional, and organic growers. Simultaneous interpretation to Spanish has been
provided. This proceedings book contains information provided on these topics by each speaker
and co-authors. The thumb drive provided in the registration packet for each attendee includes a
copy of each presentation. Thank you for attending. It is our sincere wish that this will be a very
useful meeting and that you find the accompanying materials a valuable reference! –
Bernadine Strik, Professor and Extension Berry Crops Specialist, OSU and the members of the
organizing committee
Organizing Committee
Bernadine Strik, Chair, Oregon State University (OSU)
Wei Yang, OSU. Co-chair (sponsorship coordinator), OSU
Donna Williams, Rachel Williams & team at OSU Conference Services
Dave Bryla, USDA-ARS HCRU
Chad Finn, USDA-ARS HCRU
Vaughn Walton - OSU
Steve Castagnoli - OSU
Steve Renquist - OSU
Bryan Ostlund – Oregon Blueberry Commission
Eric Pond - industry
Jon Umble – industry
Derek Peacock - industry
Steve Erickson - industry
Nancy Jensen - industry
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Table of Contents
OSU Blueberry School
Title
Authors
Characteristics of production regions in the Pacific
Northwest
Lisa DeVetter, Pat Jones, Bernadine
Strik, Kathie Dello
1
Markets - what's the future for fresh, processed, and
organic markets? Things you MUST think about before
starting or expanding production
Rod Cook, Derek Peacock, Jeff
Malensky, David Granatstein
9
Cultivar choices- Tried and true to brand new
Chad Finn and Bernadine Strik
15
Economics of production – resources
Bernadine Strik and David Granatstein
29
Resources available for selecting a good blueberry site
Wei Q. Yang
37
Site selection and establishment of a blueberry field
Wei Q. Yang and Bernadine Strik
41
Organic soil amendments and mulches for blueberry:
the good, the bad and the ugly
Dan Sullivan (OSU)
47
On-farm irrigation system design and operation
David Bryla
53
Blueberry plant physiology - why it's important to
understand the plant to manage it well
Bernadine Strik
57
Irrigation scheduling: when, where, and how much?
David Bryla
63
Pruning - impact of plant age, cultivar, and harvest
method
Bernadine Strik
69
Harvesting - hand vs. machine
Bernadine Strik (moderator); Paul
Norris (Norris Farms); Frank Brown
(Littau Harvesters (Inc.); Doug
Krahmer (Berries Northwest)
75
Nutrient management of blueberry -- assessing plant
nutrient needs and designing good fertilizer programs
Bernadine Strik and David Bryla
79
Maximizing pollination in blueberry
Ramesh Sagili, Carolyn Breece, John
Borden
95
Blueberry viruses present in the Pacific Northwest and
suggestions for their management
Robert Martin
99
Blueberry bacterial and fungal diseases
Jay Pscheidt and Jerry Weiland
107
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Page
Title
Authors
Page
Weed management for blueberry fields in the Pacific
Northwest
Tim Miller
115
Getting hit high and low: Options for managing bird
and vole damage
Dana Sanchez (OSU
125
Management of arthropods, insect, and plant-parasitic
nematodes in blueberries
Vaughn Walton,Nik Wiman, Inga
Zasada, Joe DeFrancesco, Daniel
Dalton, Amy Dreves, Jana Lee, Lynell
Tanigoshi, Wei Yang
129
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Pruning – Impact of plant age, cultivar, and harvest method
Bernadine Strik
Professor, Department of Horticulture, Oregon State University
Pruning is required to maintain blueberry plant vigor and productivity, to aid in disease and insect
management, to maintain large fruit size and quality, and to develop an appropriate growth habit for
harvesting. The cost of pruning is second only to harvesting in costs of production (see Julian et al., 2011
publications on cost of organic and conventional production). While it may be tempting to reduce
production costs through either not pruning or pruning less, this can have major consequences on yield
over time and on fruit quality. In this presentation I will discuss pruning of young and mature plants,
estimating yield through counting of buds on young plants, notable cultivar differences in pruning
method, impacts of pruning severity, pruning of rabbiteye blueberry, and pruning for hand versus
machine harvest.
Prune blueberry plants every year in “winter”. The best time to prune is from early December
through February, when plants are dormant. Blueberries produce their fruit on 1-year-old wood
(last year’s growth). Fruit buds are visible during the dormant season. They are the fat buds at
the tip of last year’s growth. The small, scale-like buds toward the base of the 1-year-old wood
are vegetative buds; they will produce a shoot with leaves next season (see physiology
presentation). Since ‘Legacy’ may not drop many of its leaves until late, it’s best to prune this
cultivar last. In addition to winter or dormant pruning, rabbiteye blueberry cultivars benefit from
summer pruning (see below).
Pruning equipment consists of high quality pruners and loppers. Gloved hands may be used to strip flower
buds off young plants and to break twigs. Some growers use hydraulic or pneumatic pruners to increase
speed. Leave the prunings between rows and chop or flail them (most common) or rake them out of the
field.
Pruning young plants
Commercial nurseries hedge nursery plants to encourage branching and maintain height – this also
reduces the development of a lot of fruit buds. However, any fruit buds present should still be removed by
pruning right after planting in fall or in spring. While some growers strip off the flowers at bloom in the
first growing season, as they feel this reduces cost, this tends to lead to a less desirable bush form on
young plants that then needs correction when pruning the following winter. In addition to pruning off the
fruit buds at planting, remove any low growth, thin or weaker growth, and any branches at the top of the
whips; this leads to a better bush shape and encourages growth of new whips at the base of the plant in the
first growing season.
Our research has shown that fruit are a very strong sink for young plants (see physiology presentation) –
the presence of even a small amount of fruit significantly reduces root, crown, and top growth of young
plants. While producing a full “early crop” in the second growing season (year 2) leads to some income
for the grower, it also reduces growth and fruit production in year 3 (Strik and Buller, 2005; see pictures
of impacts of producing a full early crop on young plants in accompanying presentation).
If plants are vigorous, growing very well in year 1, then they can be pruned to produce a limited crop in
year 2. I recommend producing no more than 0.5 to 0.75 tons/acre in year 2, depending on plant growth
and cultivar. This is difficult to do accurately without counting buds. Since having data for the Willamette
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Valley on the number of flowers per bud, average berry weight on 2-year-old plants, and percent fruit set
for many common cultivars, we can quite accurately estimate how many buds to leave per plant when
pruning and anticipated yield – see the accompanying presentation. Note that you should keep records for
flower number per bud, average berry weight, and fruit set for the cultivars you grow in your region as
these results may differ significantly throughout the PNW. We have included an excel file in the OSU
Blueberry School’s thumb drive to help you estimate yield on young plants (Yang, 2015). When you are
pruning in the winter following year 1 – to hit a low, target crop for year 2 – keep in mind that not all
plants will be vigorous enough to produce a crop. Weak plants should be pruned hard to remove all fruit,
thus encouraging more vegetative growth. It is not practical to count buds on all plants – prune several
plants to the desired bud number (generally 25 or 30 buds/plant) and then check the pruning crew
occasionally to ensure consistency throughout the field.
Pruning more mature plants
The best berries are produced on 1-year-old wood (last year’s growth, also called “laterals”) that
is from 6 to 12 inches long. This wood also tends to be of larger diameter than shorter laterals
which tends to lead to larger berries. Short laterals produce fruit, but berries are small and there
is generally little to no good shoot growth under the fruit. This leads to poor fruit quality also.
Canes or wood with a lot of short, unproductive laterals are called “twiggy" growth and should
be removed at pruning.
When pruning blueberries, keep in mind the following principles:
o Keep the bush fairly open. Open bushes promote better air circulation (less disease and
better spray coverage) and good light penetration to improve fruit bud set for next year's
crop and increase whip growth from latent buds (see physiology presentation).
o Cut out any wood that’s dead, damaged, or diseased.
o Remove the low growth that would touch the ground when loaded with fruit. Cut out
short, soft, new shoots that developed from the base of the plant late in the season.
o Remove whips smaller than pencil size in diameter, but leave larger whips to develop
into good fruiting wood next year. If needed, thin to the best 3 or 4 whips.
o Cut out unproductive canes or twiggy wood by cutting back to the crown or to a strong
new whip growing lower down on the cane. Do not be afraid to cut out a large older cane,
if it’s warranted.
o Selectively prune to keep the most production laterals (generally 6 to 12 inches long).
However, vigorous plants may still produce too much fruit if these are all left on the
bush. See the impacts of pruning severity below.
o Thin the remaining wood to balance expected fruit crop with the vigor of the bush – this
takes experience and is dependent on cultivar. See suggestions for thinning methods
below.
o Prune a weak plant harder (more) than a normally growing plant.
Cultivar specific pruning. Some cultivars (e.g. ‘Duke’, ‘Berkeley’, ‘Bluejay’) do not produce
many whips from the base of the plant. Instead they produce whips from the base of older canes
between ground level to about knee height. When you prune these bushes, you will have fewer
canes at the base of the plant, but more new growth or renewal wood higher up on the bush. Less
production wood or sections of canes will thus be cut back to these new whips. Some cultivars
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(e.g. ‘Draper’) produce many whips from the base and thinning/removing these adds
considerable pruning time.
Some cultivars (e.g. ‘Liberty’, ‘Elliott’) produce a lot of laterals on a 2-year-old cane, for
example. Generally, a cane such as this can only support fruit production on 4 to 5 laterals and
still get large fruit and good shoot growth – if too many laterals are left on a cane then berries
will be small and shoot growth will be poor. Then next winter, the cane will have “fruited out” –
be twiggy at a relatively young age and need to be pruned out. In cultivars that produce many
laterals on a 2-year-old cane, thin to the best (often longest) 4 to 5 laterals by removing the small
ones using a gloved hand. These types of canes can be tipped (removing the top laterals) if the
cane is too high and thus would be above picking height.
Some cultivars (e.g. ‘Draper’, ‘Bluegold’, ‘Reka’, ‘Elliott’) produce very long laterals or whips
with a very large proportion of fruit buds. If all these fruit buds are left on the lateral, the fruiting
area is generally very tight (berries grow tightly and are hard to pick) and the berries are small.
This type of lateral can be headed back, pruning off some of the flower buds at the tip.
‘Legacy’, a relatively new cultivar to western Oregon (not widely adapted beyond the more
temperate areas of this region – see “physiology” and “cultivar” presentations), grows quite
differently than other northern highbush cultivars. If this cultivar is fertilized with high rates of
nitrogen (see nutrient management) or is pruned too severely (hard) then the plant grows very
vigorously and sets fewer fruit buds resulting in a lower yield. ‘Legacy’ has a more weeping
habit (benefits from trellising), resulting in new, renewal growth originating from quite high up
on the bush. This cultivar is also productive on shorter laterals than others and thus, for high
yield, should be pruned to include a broader range of fruiting wood. While this cultivar takes
longer to prune than many others, it also produces a higher yield (greater returns).
Some cultivars (e.g. ‘Duke’, ‘Elliott’, ‘Legacy’, ‘Ozarkblue’) branch naturally at the tip of upright growth
during the season. The following winter, if all the branches are left on these more vigorous laterals, the
subsequent growth can end up looking like a witch’s broom. In ‘Duke’ and ‘Elliott’, thin vigorous
branches to leave the best one or two as this improves fruit quality and shoot growth the following season
– this is not necessary in ‘Legacy’ or ‘Ozarkblue’ based on my experience.
Rabbiteye blueberry plants benefit from summer pruning. Tip the vigorous shoots by removing about 1
inch of growth (“soft tip”) in early summer. It’s important to not tip too late as growing shoots to do set as
many fruit buds (see physiology presentation). Soft-tipping shoots decreases vigor of the resultant
branches and thus increases fruit bud set and yield.
While summer pruning, using hedging, is commonly done after harvest on southern highbush and
rabbiteye blueberry in the southeastern US and in Mexico and other warm regions, it cannot be done on
rabbiteye or on northern highbush blueberry cultivars in our region as the growing season is too short –
would lead to limited fruit bud set (see physiology section).
Pruning for hand versus machine harvest
For hand harvest, keep bushes within easy picking height and remove low-fruiting branches or canes.
Otherwise, prune them using the general methods described above and consider pruning severity (see
below).
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Plants to be machine harvested should be pruned to a more upright habit with a narrow crown to allow
close fitting of catcher plates and minimize fruit loss or drop to the ground. This should ideally be done
during planting establishment, as converting mature plants to a narrow crown by cutting off big canes
reduces yield significantly. In addition, remove low growth – growth that would drop below the height of
the catcher plates on the machine harvester when loaded with fruit. Bushes that will be machine harvested
for the processed market can be pruned less severely than those for the fresh market or for hand-harvest;
pruning less severely decreases berry size (see below) – this is less of an issue for processing and machine
harvest. However, wood that is too twiggy should not be left as this can break off and end up in the
machine harvested product increasing sorting costs. Keep in mind that a well pruned, machine-harvested
bush will have a greater fruit recovery (less loss to the ground) than a dense, less-well pruned bush.
Pruning for machine harvest for fresh market requires heavy pruning (as for hand-harvest) in addition to
pruning to a narrow crown – larger berries and less loss as well as more concentrated ripening is of
benefit when machine picking for fresh. Note that this method of harvest for fresh is not “easy” (see
harvesting panel article).
Pruning severity
In general, pruning reduces yield. However, annual pruning leads to consistent production of high quality
fruit.
If bushes are pruned only occasionally, then many young canes will be produced the year after the heavy
pruning. These canes will age together, and become unproductive at the same time. After several years,
when there’s a need to prune out the unproductive canes, nearly the entire bush would have to be
removed. In addition, no young growth would be present to replace the lost fruiting wood. Bushes that
have been left un-pruned for many years may need to be renovated (see below).
Irregular pruning results in erratic yields from year to year and very large bushes with individual canes
competing for light. Research has shown that annual, moderate pruning results in bushes with the fewest
canes, but with the greatest yields.
Pruning severity may need to be adjusted to balance the production of a good, quality crop with adequate
growth for subsequent years’ crops. Experience is the best guide for proper pruning.
When plants are pruned too lightly, yield may be high, but berry size is reduced, fruit ripen later than
“normal” for the cultivar and fruit quality, particularly sugar content and fruit color, may be low. In
addition, these plants become dense, with weak, twiggy growth, and fail to develop strong new wood for
future fruit production. In contrast, pruning too severely reduces yield – the increase in berry size that
results from pruning cannot compensate for the reduced berry number. Fruit would ripen earlier and the
season would be more concentrated than typical for the cultivar. There would be a lot of vegetative
growth as the plant would be out of balance (see above and physiology presentation). Thus annual
moderate pruning leads to the most consistent production of high quality fruit.
Renovation
Bushes that have been neglected or have not been pruned well for many years often have no good wood
to prune back to (laterals 6 to 12 inches long or new whips). These plants would benefit from renovation
or rejuvenation. Cut the bush to about a height of 1 ft. Thing the old canes to the best 8 to 10. The
following growing season, provided the soil and nutrient status are good and there are no pest issues,
many new whips will be produced. These can be soft-tipped to encourage branching at different heights.
Next winter, thin these to the best 12 or so. The plant will soon be back in production. This has worked on
all cultivars that it has been tested on.
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For more information see:
“A Grower’s Guide to Pruning Highbush Blueberries” (DVD 002) available from Oregon State
University: https://catalog.extension.oregonstate.edu
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