Strawberry

Lecture Outline

Reading Chapter 3 Small Fruit Crop Management

Modern Cultivated Strawberry

Family: Rosaceae

Genus: Fragaria

Species: Fragaria X ananassa

interspecific hybrid

Fragaria X ananassa Pineapple strawberry is a hybrid between

F. virginiana Virginia or scarlet strawberry

F. chiloensis Chilean or beach strawberry

History of development

Europe 1500-1800 Three common types

F. vesca Wood strawberry

F. moschata Musky stawberry

F. virginiana Virginia or scarlet strawberry

Development of Fragaria X ananassa interspecific hybrid.

F. virginiana from North America to Europe (early settlers)

F. chiloensis from Chile to Europe (Amedee Fancois Frezier)

Natural crossing occurred in mixed plantings. Seedlings produced from seeds from the F. chiloensis plants turned out to be much better fruit than either parent.

Strawberry Production (US)

Acres lbs

US Total 53,477 1.5 billion

1. California 27,582 1.3 bil

2. Florida 6,056 128 million

3. Oregon 4,413 42 mil

4. New York 1,538 5.0 mil

5. Michigan 1,498 5.6 mil

6. Pennsylvania 1,409 5.6 mil

7. Washington 1,268 8.0 mil

8. Wisconsin 1,011 4.0 mil

14. Indiana 472 1.5 mil

Plant morphology

A. Crowns

Shortened stem

Leaves at close interval

Terminal inflorescence

Axillary buds

Two types of stems

Short = flower stalk

Long = runner (stolon)

Branch crowns

Important source of additional flower stalks in some production systems

B. Runners

Prostrate stolons (specialized stems) with 2 nodes

2nd node develops into a daughter plant

Cultivars differ in their tendency to produce runners

C. Leaves

Compound, pinnate, trifoliate

Arranged in 2/5 spiral around crown

Some species (cultivars) are evergreen

D. Roots

Adventitious from base of new leaves on crown

2/5 spiral around crown

Two types of roots

Primary (permanent, structural, support)

Secondary (temporary, fibrous, nutrient and water uptake)E. Flower Stalks & Flowers

Scape - flower stalk

cyme - inflorescence

F. Flowers

Perfect (both sexes)

Complete (all 4 basic parts)

5 petals

2 rings of 5 sepals = cap

Recepticle -swollen tip of the pedicel (stem)

Ovaries - embedded

Stigmas & styles - protrude

G: Fruit

“Berry” = ripened seeds + swollen recepticle

Seeds = achenes (true fruit)

Recepticle = specialized stem tissue

Fruit ripen 20-30 days from bloom

Primary, secondary, tertiary flowers/fruit in each ‘cluster’ (cyme)

Primary flowers = largest fruit, first to ripen

Secondary flowers = moderately large fruit, main crop

Plant Development

Root Growth - Best at cool temps (~55˚F)

Crown Growth - Best at moderate temps (~65˚F)

Leaf Growth - Best at mod - high temps (~75˚F)

Fruit Development - Best at cool temps (~45˚F)

Runner Production - Best under long days and high temps

under Short days - need high temps >75˚F

under Long days - best at high temps, but capable at lower temps
Flowering Types

Flowering and fruiting in strawberries is a very complex process dependent on a series of growth steps that establish and develop the plant body along which potential flowering sites are produced. The conversion of buds from vegetative to fruiting depends on temperature and photoperiod.

Strawberry cultivars fall into one of three classes with respect to flower initiation and development: They flower once, twice, or more than two times per year.

Once = ‘Junebearers' or 'short-day' types.

Most cultivars flower once per year and are referred to as 'Junebearers' or 'short-day' types.

They require daylengths of shorter than 14 hrs or temperatures less than about 59 F for flower induction. Induction occurs in the fall and flowers develop in the spring

Can initiate flowers continuously under cool temperatures

Twice = ‘Everbearing’ types or long-day responsive

Typical of many wild species

A few cultivated types, but not commercially grown to any extent

Usually produce a spring and fall crop, but vary greatly in time of production

More than two times = ‘Dayneutral’ types

Insensitive to photoperiod for fruit bud initiation

Can initiate flowers continuously if temperatures are ‘moderate’

Usually produce in cycles of 6 weeks

Classified as weak, intermediate, strong

e.g. Weak dayneutrals are like Junebearers

Flower Development

Induction occurs in leaf after exposure to repeated short days and/or temperatures

Initiation physical and chemical changes occurs in bud upon receipt of stimulus from leaf

Differentiation development of floral organs in the bud

Development visible expansion of the flower cluster out of the bud

Pollination

Most varieties are self-fruitful but insects are essential for optimal pollination.

Some pollen is moved by wind, but complete pollination is only possible with insect activity. Bees are the best pollinators.

There are up to 500 pistils on each receptacle that develop into an “achene” or seed.

Seed development is necessary for receptacle enlargement.

Complete pollination of all ovules is necessary for maximum fruit size and perfectly shaped fruit.

Frost Protection in Strawberries

Strawberry flowers and fruit as susceptible to frost injury any time after bud break. Frost risk is high during the time of year that strawberries flower and fruit (April-June) so crop loss can be severe if frost protection is not provided.

Overhead irrigation for frost protection:

Principle: As water freezes, heat is released (energy is released in the form of heat as water becomes ice).

As long as an adequate layer of FREEZING water covers the flower or fruit, the temperature will remain at or above freezing (30-32˚ F). This is a few degrees above the critical temperature of the flower or fruit so irrigation will provide protection against freeze damage.

The rate that water freezes is dependent on environmental factors such as air temperature, humidity, and wind speed. Generally, the lower the air and dew point temperatures, and/or higher the wind speed, the greater the rate of freezing. At higher rates of freezing, higher rates of water application are necessary. Generally, application rates from 0.10 to .050 inches per hour are necessary to effectively provide frost protection.

Water application must begin BEFORE critical temperatures are reached in the plant canopy.
Production Systems:

Matted row (standard production system in the Midwest)

18-24 inches between plants

42-52 inches between rows

Plant dormant crowns as early in spring as practical, remove flowers to promote runner development, position runners during season to establish optimum density of 4-6 plants per foot of row. Overwinter with straw mulch. Fruit production starts 1 year after planting. Renovation after harvest allows development of new replacement runners and continued production over a few to several years. Weed control is the biggest problem.

Ribbon row (modification of matted row to get early production and cash returns, not widely used)

3-6 inches between plants

36 inches between rows

Plant dormant crowns at high density, straw mulch between rows, do not remove flowers, harvest fruit during first season, remove runners, overwinter with straw mulch, harvest main crop 1 year from planting, renovate after harvest, planting reverts to matted row system during second season.

Waiting beds (modification of matted row to get fruit production during the late summer, not used much)

The plants are specially treated in nursery production to grow large and develop flower buds. They are fall dug and cold-stored until the following summer when they are planted. Plants are allowed to fruit immediately after planting (in about 60 days). This allows growers to obtain fruit throughout the summer by staggering planting dates as needed. It works best in areas with cool summers (temps less than 80 ˚F).

Annual Plasticulture (standard system used in California and Florida. Becoming more popular in the SE-Midwest.)

Double rows of plants are set through black plastic mulch on raised beds in late summer when daylength is decreasing and little runnering occurs. Plants produce large crowns in the fall and fruit in the spring. High density of plants results in high yields. Varieties well adapted to the system produce large fruits with good flavor.

Trickle irrigation is used under the plastic and overhead irrigation used during plant establishment and for frost protection.

The black plastic and raised beds promote early flowering and fruiting. Plants are removed after the first harvest. With annual plasticulture pest problems such as weeds, diseases, and insects are reduced because plants are replaced each year and grown on plastic.

The system is expensive to utilize, but high returns are possible because of reduced labor, high yields, and potential for early harvest when market prices are high.

The system is less suitable for colder northern climates because the fall growth period is shorter and risk of spring frost is greater. However, some growers are modifying the system to perform more satisfactorily in the Midwest. By using different varieties, different planting stock, and planting earlier in the summer, growers have been successful raising strawberries on plastic.

Dayneutral strawberry production (works best in areas with cool summers e.g. temps less than 80 ˚F).

By utilizing dayneutral varieties growers can produce fruit throughout the summer and fall of the planting year. It provides new marketing possibilities during the off season. Dayneutral production is more labor intensive than standard Junebearer production, but since the value of the fruit is so high during the off-season the extra costs may be justified if a reliable market is available. These varieties are best suited to production in areas where summer temperatures are relatively cool, less than 80 ˚F, because fruit quality will be poor at warmer temperatures.

Plastic Tunnels and Greenhouses

Strawberries can be grown in controlled environments for off season production. These systems can range from standard greenhouses to plastic tunnels over raised beds in the field. Proper crop management is critical for producing good crops of fruit consistently.

Renovation of Matted Row Strawberries

Matted row strawberry plantings must be renovated after harvest to establish new crowns for next year’s crop. Renovation should be started immediately after the harvest is completed to promote early runner formation. The early a runner gets set, the higher its yield potential.

1.Weed control: Annual broadleaf weeds can be controlled with 2,4-D

Grasses can be controlled with sethoxydim (Poast)

Do not tank mix Poast and 2,4-D.

2. Mow the old leaves off just above the crowns 3-5 days after herbicide application. Do not mow so low as to damage the crowns.

3. Fertilize the planting. According to soil test and foliar analysis

4. Subsoil between rows to break up compacted layers and provide better infiltration of water.

5. Narrow rows: Reduce the width of rows to a manageable width based on your row spacing. A desirable final row width to attain at the end of the season is 12-18 inches. Wider rows lead to low productivity and increased disease pressure. Rows can be narrowed to as little as 6 inches during renovation. Since more berries are produced at row edges than in the middle, narrow rows are superior to wide rows. Narrow rows will give better sunlight penetration, better disease control, and better fruit quality.

6. Cultivate: Work in straw between rows and throw a small amount of soil over the row by cultivation. Strawberry crowns continue development at the top, and new roots are initiated above old roots on the crown, so 1/2 - 1 inches of soil on the crowns will facilitate rooting. This also helps cover straw in the row and provides a good rooting medium for the new runner plants.

7. Weed control: Pre-emergence weed control should begin immediately. Sinbar or Devrinol are suggested materials. Devrinol must be incorporated by irrigation, rainfall, or cultivation to be effective. Rate and timing of Sinbar application is critical. If regrowth has started at all, significant damage may result. Some varieties are more sensitive to Sinbar than others. If unsure, make a test application to a small area before treating the entire planting. Sinbar should not be used on soils with low organic matter, or on sensitive varieties like Guardian, Darrow, Tribute, Tristar and possibly Honeoye. If Sinbar gets onto strawberry leaves, irrigate to wash it off.

8. Irrigate: Water is needed for both activation of herbicides and for plant growth. Don’t let the plants go into stress. Ideally the planting should receive 1 to 1-1/2 inches of water per week from either rain or irrigation depending on soil type. Strawberry roots are shallow. Irrigate frequently in amounts necessary to penetrate the top 6-10 inches of the soil.

9. Cultivate to sweep runners into the row until plant stand is sufficient. Thereafter, or in any case after September, any runner plant not yet rooted is not likely to produce fruit next year and is essentially a weed and should be removed. Coulter wheels and/or cultivators will help remove these excess plants in the aisles.

10. Adequate moisture and fertility during August and September will increase fruit bud formation and improve fruit yield for the coming year. Continue irrigation through this time period and fertilize if necessary. An additional 20-30 pounds of N per acre is suggested, depending on the vigor.

Strawberry Weed Control

Weeds are a major problem in strawberry production and one of the main reasons that a planting declines in productivity over time.

Stage of Weed Control

Pre-plant

Fumigation

Cover cropping

Post-planting

Pre and post-emergent herbicides

Cultivation

Renovation

Pre and post-emergent herbicides

Cultivation

Tips for herbicide use

Know your soil type

Know your weed species

The current problem in commercial strawberry production (matted row system) is the lack of available herbicides (those registered for use on strawberries). The IR-4 project is trying to identify potential products and push registration through EPA, but as of August, 2000 there are only two pre-emergent materials available for use on strawberries; Sinbar and Devrinol.

Strawberry Diseases

Gray Mold (Botrytis cinera)

Most important flower and fruit pathogen of strawberries worldwide.

Cultural controls:

· Good sanitation (fungus survives in dead leaf material)

· Management of vigor (excess vigor leads to rank foliage and more disease pressure)

· Narrow rows on raised beds

· Straw mulch prevents fruit from touching soil and becoming infected

Chemical Controls:

· Most infections occur at bloom and fruit rot occurs as fruit ripen. Secondary spread of spores can lead to infections of ripening fruit.

· Selected fungicides applied at bloom

Elevate, Rovral, Benlate, Topsin-M plus captan or thiram

Black Root Rot

Disease complex caused of fungi, nematodes and environmental stress

Cultural control:

· Select site with well drained soils

· Maintain good plant health

· Avoid water stress, winter injury, and herbicide injury

Chemical control:

· Pre-plant soil fumigation is the only control

Leaf Spots

Leaf scorch Diplocarpon earliana

Leaf blight Phomopsis obscurans

Leaf spot Mycosphaerella fragariae

Damage is usually minor, so control is not normally necessary.

Control:

· Good resistance in many cultivars

· Fungicide sprays if necessary

Leather rot Phytophthora cactorum

Fruit becomes tough and leathery

Control:

· Avoidance is the best control.

· Prevent fruit contact with soils by mulching with straw between the rows

Red Stele Phytophthora fragariae

Can be a major problem on poorly drained soils.

The fungus survives many years in the soil.

Many resistant cultivars available.

Control:

· Avoid poorly drained soils, plant on raised beds

· Plant resistant cultivars

· Fungicide specific for Phytophthora (Ridomil or Aliette)

Anthracnose Colletotrichum spp.

Causes a fruit rot, crown rot, and petiole and runner lesions. Different species of the fungus are implemented in various symptoms.

Crown rot phase is the biggest problem and is worst in the SE US in production fields and nurseries.

Control:

· Plant certified disease-free plants

· Avoid poorly drained soils, plant on raised beds

Strawberry Insect Pests:

Scouting for insect presence and damage is the key to controlling insect damage in strawberries.

Direct pests (attack fruit and flowers)

1. Strawberry Weevil or Clipper

Adults feed on pollen of unopened flowers and the female lays an egg in an unopened flower then “clips” the stem of the bud, leaving it hanging from the plant.

Control: Insecticides timed according to scouting results

2. Tarnished Plant Bug

Adults and nymphs feed on seeds of developing fruit. This leads to misshapen fruit.

Control: Insecticides timed according to scouting results

3. Strawberry Sap Beetle

Adults feed on ripe fruit causing holes and cavities usually on the underside. Insects seldom found in the holes. Favored by mulch.

Control: Sanitation, bait buckets, insecticides

4. Slugs (not an insect, but still a problem)

Adults feed on ripening berries, leaving holes that can be anywhere on the fruit, especially under the cap, making it easy to differentiate from sap beetle damage. Favored by mulch.

Control: bait with metaldehyde bait or beer

Indirect pests (attach leaves, roots, and crowns)

1. Leafhoppers (especially potato leafhopper)

Piercing-sucking feeding causes leaf distortion and reduced photosynthesis

2. Strawberry Leafroller

Larvae feed on leaves

3. Meadow Spittlebug

Nymphs form spittle mass in crown, feed by piercing-sucking and cause plant stunting and reduced berry size

4. Strawberry Aphids

Piercing-sucking feeding results in reduced vigor. Important vector of virus diseases.

5. White Grubs

Larvae of June beetles and Japanese beetles feed on roots and are especially fond of strawberries. Most important in new plantings if the site was in sod prior to strawberries.

6. Root Weevils Strawberry root weevil and Black vine weevil

Adults eat notches in leaves which is a diagnostic sign that the larvae are present and feeding on the roots.