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Experiences Re-planting

Blueberries in NC

Bill Cline, Entomology and Plant Pathology

North Carolina State University

“ The Southern Highbush

[Blueberry] is a plant looking for a

place to die”

Gerard Krewer, Dixie Blueberry News, March 2003

Woody Perennial Crops Disease problems and

plant losses are additive – no “starting over” with each new growing season

Biocidal treatments or rotation cannot be used on an annual basis

Pathogens and insects are often plant-borne, chronic

Errors (site selection, lack of drainage) hard to correct

‘Legacy’ Blueberry

Vegetatively

Propagated

Diseases may be

transmitted via cuttings

from infected plants

Clonal -- no multi-line

resistance

Some diseases are

unique to plant

propagation systems

Softwood blueberry propagation

Site selection/preparation

What are the horticultural requirements of the crop (Soil type, pH, fertility, organic amendments)?

Drainage is very difficult to correct AFTER the plants are in the ground

WHAT MAKES A GOOD BLUEBERRY SITE? –

Ashe County, WNC Bladen County, SENC

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Good drainage, soil aeration, low

pH, organic matter and water

pH Highbush blueberry -- 4.0 to 5.0

Rabbiteye blueberry – 4.5 to 5.3

Drainage Surface drainage (bedding, ditching)

Internal drainage (soil amendments if needed)

Irrigation Overhead (allows frost protection)

Drip or micro-sprinkler (conserves water)

Reasons to re-plant a site

Replacing older cultivars

Plant stand getting thin (<75%)

Correct drainage problems

Organic matter depleted (re-mulching)

Chronic disease losses (canker, viruses)

Herbicide injury, weed pressure

Northern highbush ‘Croatan’

phased out in NC in the last 10 yrs

1950s, selected for

canker resistance

Productive and

vigorous

Berry medium, soft

Phased out with

introduction of

packing lines

Diseases –

Fungi – Stem canker, stem blight,

Ganoderma

Viruses – Blueberry red ringspot

Phytoplasma – Blueberry stunt

Blueberry Stunt Phytoplasma Stem Canker (Botryosphaeria corticis)

1940s-1970s - in NC ,

canker devastated

‘Weymouth’, ‘Wolcott’

Newer cultivars selected

for resistance

Benlate (1970s)

Better cultural practices

More cvs (multi-line?)

Softwood and tissue

culture propagation

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Blueberry Red Ringspot Virus

Ganoderma rot (fungus)Stalked, one-sided polypore mushrooms –

“Conks” are woody, spores are released

from tiny pores rather than gills

Associated with dead/dying

bushes, mostly O’NealWhy not rotate to a new field?

Land ownership

Other sites not suitable

Convenient location

Good PYO site

Customers/historical

Restrictions on clearing “new ground”

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Reasons to re-plant or partially

re-plant a young field

Did it wrong the first time (no irrigation,

high pH, inadequate drainage)

Blueberry stem blight in yrs 2 & 3

Add pollinator row

Hot spots of injury to roots by insects

Herbicide injury from adjacent property

Stem Blight (Botryosphaeria spp.)

Wounding required for infection, epidemics can be traced back to specific injury events

Fall freeze injury predisposes plants in overly fertile soils (site selection)

Fungicides not effective

Young bushes at greatest risk (juvenility)

Pruning Young Bushes (0-3 yrs)

Removal of flower

buds to prevent

overcropping

Winter pruning to

shape the bush

Removal of succulent

fall shoots to avoid

stem blight infection

Cold-injured shoots are susceptible to

infection by stem blight fungi

In winter, hand-remove cold-injured shoots in 2- & 3-yr-old fields

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Insects attacking crowns/roots

Grubs

White-fringed beetle

Prionus (longhorned beetle)

Stem borers

WFB -- dieback of young ‘Legacy’ bushes on

plastic in a roughly circular half acre area

Affected plants were found to have almost no hair roots

remaining due to insect feeding damage

Excavation revealed larvae and new adults of

White-Fringed Beetle

Check crowns for larvae in older

bushes

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Prionus larvae June 3Forestry herbicide drift, Summer

following application

“Replant Disorder” – multiple

contributors to the problem

Inadequate site renovation (aeration,

organic matter, fertility)

Ring nematode and others (GA), possibly

Awl nematode in NC

Phytophthora root rot

Soil-borne plant pathogenic fungi

Weeds Sites with overhead irrigation may not be adequately renovated

on the irrigation row. Growers are reluctant to move (cap or

replace) buried irrigation lines, try to work around them.

Replant Diseases and Disorders

Phytophthora root rot

Nematodes

Soil-borne fungi

Lack of aeration

Depleted organic matter

Cultural practices

Controlling Blueberry Root Rot

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Root rot symptoms

Loss of vigor

Wilting, stunting

Yellow leaves

Poorly anchored

Early reddening

Defoliation

Tip dieback

Death

Phytophthora spp.

Blueberry root infection by the

pathogen Phytophthora cinnamomiYellowing and leaf drop due to root rot

Contributing factors for root rot

Usually in poorly drained areas with saturated soils (swimming spore!)

Inadequately bedded (flat) rows

Heavy soils (poor internal drainage)

Susceptible cultivars (Southmoon, Southern Bell, Other SHB?)

Poor sanitation, especially infected transplants (usually potted plants)

Pond water contamination?

Control methods

Drainage is the only lasting solution

Site selection -- some soils were not

meant to grow blueberries!

Resistance is not really available

Use sanitation in the nursery to avoid

introducing disease into new fields

Chemical control – not recommended in

North Carolina

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Drainage considerations

Provisions for field drainage must be

made prior to planting

Bedding up of rows should be done prior

to planting

If soil is too heavy (poor internal drainage)

the soil must be amended prior to planting

V-plow used to sweep middles

Sweep (front view) Tapered disk

Total width of disk

based on your row

spacing

Series of blades from

large to small on the

same spindle

Mounted on 3 pt hitch

Rows bedded with a tapered diskPhytophthora root rot can be severe on Fraser fir

planted on poorly drained sites/heavy soils

“As growers have tried

to expand plantings to

lower elevations and

heavier textured soils,

losses from this disease

can reach 30% to 75%

in unfavorable sites.

Because infested sites

can no longer be used to

produce noble and

Fraser fir, this disease

severely limits the ability

of growers to increase

the production of these

species” (Chastagner &

Benson, PHP, 2000)

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Root Rot in Bark Bed Systems in Georgia

Phytophthora, Pythium and Rhizoctonia reported

as causal agents

Disease problems have been reported even

when new bark is used (plant borne pathogens?

Infested irrigation water?)

Phosphite-treated bush (left) vs untreated, in bark beds at Griffin, GA. Control

has been demonstrated for both Phytophthora and Pythium. Photo courtesy Dr.

Phil Brannen.

Ring Nematode has been associated with replant disorder

in Georgia. Surveys in GA and NC did not show a similar

trend in NC, but other species were present --

Female, length < 1.0 mm

Image courtesy Phil Brannen, UGA

Disease Management Strategies

To be Considered Before Planting:

Geographic location

(avoidance)

Site selection

Site preparation

Cultivar resistance

clean planting stock

Red Ringspot VirusFrom infected nursery stock

Basic steps to establishing a new

blueberry planting:1. Select a well-drained site in full sun with an open,

porous soil – avoid clay soils.

2. Acidify the soil as needed for a pH of 4.0 to 5.0.

3. Have your soil tested, and adjust fertility levels (N-P-K) according to soil test results.

4. Purchase the correct species and cultivar(s) for your soil type and location.

5. If needed, add acidifying organic matter (peat moss, pine bark, or aged sawdust) to the soil.

6. Mix and mound the amended soil to form raised beds or raised rows before planting.

Basics of establishment (continued):

7. Plant dormant bushes in raised beds or rows, usually in late winter (Feb-Mar).

8. Prune at planting to keep only 3-4 upright shoots, and to reduce height by one-half to two-thirds.

9. At planting, remove all flower buds to prevent fruit production in the first year.

10. Provide water -- irrigation is essential for establishment and survival.

11. Maintain a weed- and grass-free zone around each plant.

12. Apply a 3-4-inch layer of surface mulch (pine bark, pine needles, wood chips, or woven plastic mulch).

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Blueberries on volcanic soils in Chile. Raised

beds, drip irrigation, mulch amendments, fertility

and pH adjustments through the drip line.

Early-ripening southern highbush in

bark beds, south Georgia, 2009

Bark mulch added to increase organic matter,

lower pH and improve drainage (note raised beds)

Surface mulch holds moisture and suppresses weeds. Use

organic mulch (bark, wood chips, pine straw), black plastic,

or weed barrier fabrics.Additional Considerations

Deep plowing may be needed prior to

bedding

Weed control (and pH, mulch) may take a

year to get right

If sulfur is needed for pH lowering, apply a

year ahead of time, and re-test

Drainage and raised beds are best

addressed before planting

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Continued -- Re-bedded area should be raised and

“fluffy” enough to plant with bare hands

Tissue culture plants are preferred, “Start

Clean and Stay Clean”

Buy extra for re-sets, double set a few

Weed matting or plastic (fumigation?)

recommended on previously planted areas

Irrigation is essential