Strawberry Harvest and Problems

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Harvesting Strawberries
and Treating Problems

 In this Series 
Grapes
Bush Berries
Strawberries

High yields of quality strawberries require vigorous growth and healthy plants. Growth can be affected by many different factors such as soil fertility, lack of moisture, weeds, insects, and diseases. 

 

Growers can control all of these factors, while certain factors, such as weather conditions, cannot be controlled. Growers can also control plant growth characteristics, productivities, and blossom hardiness by selecting different varieties. 

 

A sound strawberry production program should include the control of all pests and the use of good cultural practices. A total program replaces most of the “luck factor” and results in excellent crop production yearly.


Harvesting


Harvest strawberries when the berry is fully ripe. The first harvest can occur approximately 30 days after first bloom. Check the planting every other day for ripe fruit. White areas on the berry indicate immaturity. Allowing the berry to reach full color on the plant increases the sugar content and the size of the berry. Pick the berries with the stem and cap attached to allow the fruit to keep for a longer period. Berries that have their caps removed or are injured become inedible, and also lose their vitamin C content within 48 to 72 hours.


pickstraw1.gif (125x121 -- 5228 bytes)pickstraw2.gif (110x125 -- 5668 bytes)To pick without bruising, slip your index and second fingers behind a berry with its stem between your fingers, twist the stem a bit and pull with a sharp jerk.  The stem will snap off about 1/2 inch from the berry (see diagram on left).  

If the berries are large and thick-stemmed, cradle each one in your hand and pinch off the stem between your thumbnail and index finger (see diagram on right).

  • Pick only the berries that are fully red. Part the leaves with your hands to look for hidden berries ready for harvest.
  • Pick the row clean. Remove from the plants berries showing rot, sunburn, insect or bird injury, or other defects and dispose of them, or keep ones with good parts separate from the healthy berries.
  • Berries to be used immediately may be picked any time, but if you plan to hold the fruit for a few days, try to pick in the early morning or on cool, cloudy days. Berries picked during the heat of the day become soft, are easily bruised, and will not keep well.
  • Avoid placing the picked berries in the sun any longer than necessary. It is better to put them in the shade of a tree or shed. 
  • Cool them as soon as possible after picking. Strawberries may be kept fresh in the refrigerator for 3 or more days, depending upon the initial quality of the berry. After a few days in storage, however, the fruit loses its bright color and fresh flavor and tends to shrivel.
  • Store in the refrigerator in shallow containers, uncovered or lightly covered.  Do not wash until ready to use.

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Problems


Strawberries are attacked by many pests and diseases that vary widely in their destructiveness and distribution. Preventative disease control measures begin with planting disease-free stock with genetic resistance and using recommended cultural practices. The production of disease-free plants and fruits may also require preventative applications of fungicides or insecticides. When using these to control pests and diseases of foliage and fruit, follow label directions and the time limit given for “last application before harvest.” 

 

Below are the pests and diseases that most often affect strawberries, and ways to control them.  For more information on dealing with and preventing fungus and insect problems, check out the Fungus Problems and Insect Problems pages.

 

Bird feeding may be a problem in some plantings. Protective netting is available from garden centers and must be put in place before the birds begin feeding on the fruit. Prop the netting two inches above the foliage and secure it around the edges to prevent the birds from being able to reach the fruit.

 

Main Causes of malformed fruit


buttonberry.jpg (136x115 -- 4497 bytes)"Nubbins" or "button berries"  (see at left) may be caused by feeding tarnished plant bugs (see below), heavy infestations of cyclamen mites, frost injury, nutrient deficiencies (boron, calcium), inadequate pollination, abnormally high temperatures that make pollen nonviable, or by the application of 2,4-D from August 1 to November 1, when fruit buds are differentiating.


Fasciated berries, those that have a cockscomb shape as if several berries have grown together with multiple tips, are caused by short day-lengths in the fall or by cold, dry weather during this time. Fasciated fruit often occurs when cultivars adapted to northern conditions are grown in the south.

 

Anthracnose Crown and Fruit Rot

 

strawanthracnose2.jpg (140x95 -- 3498 bytes)Crown rot occurs when the fungus grows into crowns from infected runners or petioles.  Plants with crown rot may die in the nursery or after being transferred to production fields.  Wilting plants with crown rot have a reddish brown, firm rot of the interior of the crown.  This can be seen most easily by cutting through the crown length wise.  Crown rot is sometimes difficult to identify on the basis of crown discoloration because crowns of dying strawberry plants turn brown regardless of what kills them.

strawanthracnose1.jpg (150x84 -- 3723 bytes)Fruit rot can occur on both ripe and unripe fruit.  Infected tissue on ripening fruit appears as round, firm, sunken, tan to brown spots that turn into sunken black lesions with age.  Spots may remain a light tan for a few days, especially during wet weather.  The entire fruit may become infected, dried, and mummified.  Dark brown to black, firm lesions can occur on green fruit of susceptible cultivars.

Sources of anthracnose are difficult to determine.  The fungus can survive for several months in soil or on plant debris.  Anthracnose may also survive on alternate hosts during the summer.  Infected transplant material can act as the primary source of the disease.  Anthracnose is favored by warm to hot, wet conditions with high relative humidity.

Control of anthracnose begins by transplanting disease-free material.  Follow a protective fungicide program from transplanting through harvest.  Avoid overhead irrigation if possible.  If fruit rot occurs, remove all infected fruit at each harvest.  To prevent spread of the disease, pickers should never move from an infected to a non-infected field.  Strawberry varieties resistant to anthracnose are currently being developed.

Foliage Diseases


Leaf symptoms appear as white patches of mycelium on the lower leaf surface. The entire lower leaf surface may be covered, the leaf edges roll upward, and purple to reddish areas develop on the lower leaf surface. Losses result from infection of flowers and fruits, while leaf infection has not significantly reduced yields. A high degree of resistance is present in many cultivars.

2Leaf_spot_2t.jpg (140x93 -- 3097 bytes)Leaf spots.
This complex of foliage problems includes: Leaf Scorch (Red Spot), Leaf Spot, Purple Leaf Spot, and several other leaf diseases. The symptoms are characterized by numerous irregular purple blotches, round lesions with red rusty borders and white centers, or spreading lesions that cover nearly the entire leaflet. Leaf diseases survive the winter on infected leaves as conidia or other over wintering fungal structures. The new disease cycle begins when rain or wind disperse fungal material to new leaves. Mid-age leaves are most susceptible and protective fungicides are required when susceptible cultivars are grown. Resistant cultivars of pathogen-free stock are desired.

Slime molds.
Slime mold fungi may be found on strawberry plants and mulch during the warm, wet weather of spring or fall. This creamy white or tan colored, jellylike mass moves out of the soil and up onto leaves and grasses. It produces variously shaped and colored, crusty structures with powdery dry spores. Slime molds are found on fruit grown under plastic. These fungi are not parasitic to plants but can smother single leaves or fruits and be unsightly. Slime molds disappear when hot dry weather returns and do not require treatment.


Root and Crown Diseases


Red Stele.
Diseased plants occur in patches and produce fewer runners and smaller berries. The tips of young roots rot first, after which the stele of infected roots becomes red. Lateral roots also die and decay, producing a “rattail” symptom. Red color may extend up to the plant crown. Plants may appear stunted or wilted, and leaf color may change to red, orange, or yellow. Avoid soil compaction and improve drainage. Plant resistant cultivars from inspected planting stock.

2Verticillium_Wilt.jpg (140x92 -- 4822 bytes)Verticillium Wilt.
Damage from this disease is often most severe in the first year of growth. The oldest leaves show marginal and interveinal (between the veins) browning and death, while newer leaves are stunted but remain green and don’t wilt. The symptom often appears in late spring with the onset of hot temperatures and dry periods, or with stress from high light intensity. Planting disease-free stock in soil without a history of Verticillium has been successful. However, this fungus has become widespread, so use of disease-resistant varieties and soil fumigation may be needed.

Black Root Rot.
This is caused by a complex of root-attacking fungi, injurious environmental conditions (freezing or water logging of soil), nematodes, or any combination of these factors. Infected roots turn dark and lose their feeder roots. Black root rot causes poor plant vigor. This problem is associated with soils of high clay content, excessive irrigation, and soil compaction. Avoid these soils and provide adequate soil aeration for vigorous root growth.

Nematodes.
Parasitic nematodes are small round worms that range in size from one-sixty-fourth to one-sixteenth of an inch long. Some species of nematodes cause serious damage to strawberries when they occur in high numbers. Root-knot nematodes cause characteristic knots or galls on roots.

strawnematodeleaf.jpg (122x140 -- 2780 bytes)Symptoms associated with root-knot and other nematodes: stunting, yellowing of leaves, reduced berry yields, reduced production of runner plants, wilting, and general loss of vigor. Severe infestations of nematodes on strawberry plants have been found in a few instances in Minnesota.

Nematode root diseases are almost impossible to diagnose from symptoms alone (see nematode leaf damage at left and a whole plant affected below right). To make an accurate diagnosis, nematodes must be recovered and identified from diseased plants and soil. Such a diagnosis can be made only in a specially equipped laboratory by trained personnel.

strawnematodeplant.jpg (140x93 -- 3838 bytes) The basic principle of nematode control in strawberries is planting only nematode-free strawberry plants in nematode-free soil. Eliminating nematodes from the soil is, at best, a rather expensive and difficult task. The basic method of field-scale nematode control is soil fumigation (application of chemicals). Crop rotation is generally more economical than soil fumigation if land is available.

 

Nematodes are found in the soil and are too small to be seen with the naked eye. Most nematodes feed on roots. Symptoms of nematode damage include galls on the roots or stubby, stunted roots. To avoid a buildup of nematodes, rotate plantings to a different site when establishing new beds.

Insects and other pests


tarnishedplantbug.jpg (100x100 -- 2631 bytes)Tarnished plant bugs
cause deformed or "nubbin" berries with a concentration of seeds at the tip of the fruit. Nymphs puncture individual seeds and inject a toxin so that the fleshy part of the berry stops developing where the seed was injured. Damaged seeds are hollow and turn a straw-brown color. Plant bugs are often in alfalfa; to prevent the bugs from feeding on strawberries, avoid mowing alfalfa when strawberry plants are in bloom. Go to Insect Problems for a listing of products that may be applied to control insect pests on strawberry plants.

 

Leaf rollers are small worms that roll the leaves together and feed on the leaves. They must be controlled if they become numerous.

2spotspidermite.jpg (104x100 -- 2464 bytes)Mites
are tiny, spider-like creatures that are typically found on the underside of leaves. Mites tend to be the most damaging during hot, dry periods, when they suck plant juices from the leaves.  There are two main types of mites - the red spider mite and the two-spotted mite (shown at right).

Strawberry weevils or clippers
puncture fruit buds with their snouts to feed on immature pollen. Later, females deposit an egg inside a floral bud and girdle the petiole of the bud so that it falls to the ground or is left hanging by a small bit of tissue.

Slugs
eat holes in ripe fruit and are worse during rainy weather or near rotting foliage. Shiny slime trails are evidence of slugs.

 

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