Fragaria x ananassa, more commonly known as strawberries, are a perennial in the rose family. The strawberry has an incredible reach and can be found in native forms on every major continent excepting Africa and Australasia (Australia and New Zealand).
Today, strawberries are grown in all U.S. states and Canadian provinces, with California leading production most of the year, then Florida picking up domestic supply in the late fall and winter months.
The deep red fruit was once much smaller, but selective breeding and adaptation have resulted in larger, juicier berries for the fresh market.
Strawberries are not, however, considered true berries since their tiny black seeds are on the outside instead of inside the fruit; for this reason, they are classified as “aggregate accessory fruits.”
Although most strawberries are grown for the fresh market, they are also frozen and processed into a number of items such as jams and purees.
Types & Varieties
Strawberries are generally described as June bearing, everbearing, or day neutral. June bearing refers to the two- to three-week period the crop produces fruit in the spring. These crops typically produce berries larger than everbearing and day-neutral types and are more popular with commercial growers.
June bearing types have three different varieties: early, mid-season, and late. Everbearing do not produce crops all season as the name implies, but rather once in spring and again toward the end of summer.
Depending on region, everbearing varieties can produce three crops: one in spring, summer, and fall. Day neutral types produce fruit all season long. All three types are highly susceptible to frost damage.
There are many varieties available for all types, which vary in sweetness, color, and fruit size. Varieties include Allstar, Annapolis, Carmine, Chandler, Earliglow, Florida Radiance, Fort Laramie, Honeoye, Jewel, Ozark Beauty, Seascape, Sparkle, Strawberry Festival, Surecrop, Tristar, and Winterstar.
Strawberries grow best in warm weather with low humidity making Southern California a prime location for cultivation. They are also grown in the eastern United States with smaller yields, predominantly sold through u-pick operations or farmers markets. An exception is Florida, the nation’s top strawberry producer in winter months.
Well-drained sandy loam, rich in organic matter, is ideal for strawberries. The area should be in full sun, have a gradual slope, and not previously used to grow peppers, potatoes, eggplant, or tomatoes since root rot can live in the soil and attack strawberry plants. Recently plowed areas that were previously grass are also not recommended as weeds and white grubs could become a problem for new strawberry plants.
Strawberries are picked by color and maturity and harvested by hand. New robotic pickers, being tested in Florida, may have a significant impact on this highly labor-intensive process. Berries should be picked when temperatures are cool, such as in the morning or evening.
After harvest, beds should be refruited or replanted depending on soil health. Most growers replant every 3 to 4 years to prevent disease development and reduced yields.
Pests & Diseases
Strawberry bud weevils, also called ‘clippers,’ can cause considerable damage. The females lay eggs once a year inside buds then ‘clip’ them to prevent flowering and exposure of the eggs. Leafrollers hide in cocoon-like enclosures secured with silky, white, thread-like webbing. They feed while enfolded in the leaves and then as the plant matures, work their way to the fruit, leaving tiny holes.
Strawberry aphid waste is referred to as honeydew and is the cause of sooty molds. The aphids shed their skin, which sticks to the mold and contaminates fruit. Strawberry yields can also be impacted by mites, rootworms, sap beetles, strawberry crown borers, tarnished plant bugs, thrips, and white grubs.
Botrytis rot or grey mold will grow at 32°F, albeit very slowly. Grey mold is the most common cause of postharvest fruit loss and starts as white in color, but quickly turns grey. Rhizopus rot is easily spread through airborne spores and characterized by black spots. Infected fruit will become soft and leak sticky red juice. The disease will not grow in temperatures below 41°F, so proper storage temperatures can prevent losses.
Mucor and rhizopus rot both produce soft, leaky fruit, while red stele root rot causes damage in wet winter and spring months. Plants will appear stunted and dull, with younger leaves displaying a blue-green pall. Other diseases that challenge strawberry cultivation include black root rot, leaf rot, fruit rot, blossom blight, powdery mildew, leaf scorch, and verticillium.
Storage & Packaging
After picking, strawberries are gently packed in the field and fruit should be cooled as soon as possible to maximize shelf life. Optimum storage temperature is between 32° and 34°F with 90 to 95% humidity for 5 to 7 days.
Berries will shrivel or lose color if stored too long. Mold growth is accelerated in temperatures above 36°F; modified atmosphere packaging with 10 to 15% carbon dioxide can reduce respiration, control mold, and extend shelf life.
References: Agricultural Marketing Resource Center, Cornell Cooperative Extension, Iowa State University Extension, PennState Extension, Purdue Extension, UC Davis Postharvest Technology Center, University of Illinois Extension, USDA, Washington State University.
GRADES & GOOD ARRIVAL
Strawberries are classified as U.S. No. 1, U.S. Combination, or U.S. No. 2 based on characteristics such as size, firmness, ripeness, development, and coloring, as well as being free from damage caused by mold, decay, dirt, moisture, disease, pests, and mechanical harm.
Generally speaking, the percentage of defects shown on a timely government inspection certificate should not exceed the
percentage of allowable defects, provided: (1) transportation conditions were normal; (2) the USDA or CFIA inspection was timely; and (3) the entire lot was inspected.
|U.S. Grade Standards||Days Since Shipment||% of Defects Allowed||Optimum Transit Temp. (°F)|
Canadian good arrival guidelines (unless otherwise noted) are broken down into five parts as follows: maximum percentage of defects, maximum percentage of permanent defects, maximum percentage for any single permanent defect, maximum percentage for any single condition defect, and maximum for decay. Canadian destination guidelines are 15-10-5-10-3.
References: DRC, PACA, USDA.
• If any amount of decay or mold affects a strawberry, it is scored as defective; a berry with surface mold is scored against the 5% tolerance for serious damage, while a berry with decay is scored against the 2% decay tolerance
• Sound strawberries with juice from bruised or decayed berries are also scored as defective, against the 5% tolerance for serious damage (moisture from condensation is not to be scored as a defect)
• Strawberries will be scored as defective unless there is a minimum of 75% of the surface being at least a pink color.
Source: Tom Yawman, International Produce Training, www.ipt.us.com.