July 6, 2011

Yard and Garden: Strawberries

By Richard Jauron
Iowa State University Extension Scott County

The strawberry is the most popular small fruit grown in the home garden. It is relatively easy to grow, produces large quantities of fruit high in vitamin C without requiring extra equipment and can be grown in home gardens all over Iowa. Gardeners with questions about strawberries and other berries may contact the experts by emailing or calling the ISU Extension horticulture hotline at hortline@iastate.edu or (515) 294-3108.

When should strawberries be harvested?

Harvest strawberries when the fruit are uniformly red (fully ripe). Pick the berries with the caps and stems attached to retain firmness and quality. Pinch off the stem about one-fourth inch above the cap. Don’t pull them off.

Strawberries should be picked about every other day in warm weather, every three to four days in cool weather. The harvest period for some June-bearing varieties may last three to four weeks. Strawberries can be stored in the refrigerator for up to five to seven days. Optimum storage conditions are a temperature of 32° F and a relative humidity of 90 to 95 percent.

Some of my strawberries are covered with a gray, velvety growth. What is it and how can it be controlled?

The gray, velvety growth on your berries may be gray mold. It also is known as Botrytis fruit rot. Gray mold is favored by poor air circulation and a high humidity in the strawberry planting. The most commonly infected berries are those touching the soil or other infected berries.

Cultural practices can reduce losses due to gray mold. Do not fertilize June-bearing strawberries in spring. The application of a nitrogen-containing fertilizer in spring promotes lush, vegetative growth. Dense foliage slows the drying of the strawberry planting, resulting in a more favorable environment for gray mold. Control weeds in the strawberry bed. Weeds reduce air circulation and slow the drying of the strawberry plants. Mulch the planting with straw to keep the berries off the ground. Berries resting on a damp or wet soil are more susceptible to gray mold. During dry weather, irrigate in the morning when using a sprinkler. Plants dry quickly when irrigated in the morning. “Clean-pick” the strawberry planting. Harvest frequently. Pick berries as soon as they are ripe. Handle berries carefully during harvest to avoid bruising the fruit. Immediately refrigerate the unwashed berries. Berries that exhibit symptoms of gray mold should be picked and removed from the bed. Finally, fungicides are used by commercial strawberry growers to control gray mold. However, cultural practices are the best way to control Botrytis fruit rot in home gardens.

Why do my strawberries have a slightly bitter taste?

The flavor of most fruits and vegetables is influenced by weather conditions. In regards to strawberries, warm sunny weather produces the most flavorful fruit. When the weather is extremely hot, the berries may have a slightly bitter taste. Strawberry plants produce smaller quantities of sugars when the weather is cool and cloudy. As a result, berries are not as sweet when the weather is cool and rainy in May and June. Leather rot, caused by a fungal disease, can be a problem in wet weather. Infected fruit have a leathery texture and bitter taste.

My June-bearing strawberry patch was flooded in June. Can I harvest the berries?

Berry fruits, such as strawberries, are highly susceptible to bacterial contamination. Silt and other contaminants may become imbedded in the fleshy fruit and are difficult to remove. Since the berries were present when the garden was flooded, do not harvest and eat any of the fruit. Renovate the strawberry patch in early July. Next year’s crop should be safe to eat if additional flooding doesn’t occur during fruit development.

How can I prevent birds from eating my strawberries?

Birds can destroy 20 to 30 percent of a strawberry crop. The best way to prevent crop loss in the home garden is to place protective netting over the planting. Netting can be purchased at garden centers or through mail-order catalogs. Attach the netting to a frame that sets over the strawberry planting. The netting should be kept several inches above the plants so birds can’t peck at the fruit through the netting. The structure also should be designed so the netting can be easily removed to harvest the fruit.
There are small, black, yellow-spotted beetles feeding on my strawberries. What should I do?

The small, black beetles are likely sap beetles. They are also known as picnic beetles or picnic bugs. Sap beetles commonly feed on overripe or damaged fruits and vegetables in the garden.

Sanitation is the best management strategy for sap beetles in home gardens. Keep the strawberry patch as clean as possible through timely picking and removal of damaged, diseased and overripe fruit.

Insecticide sprays are available for sap beetles, but they are difficult to use because they are applied to a crop that is ready for harvest or while harvest is under way. If you do spray, use an insecticide with a short harvest-waiting interval and follow label directions carefully.

There are small masses of foam-like material on my strawberry plants. What are these foam-like masses?

The foam-like masses on the strawberry plants were probably created by the meadow spittlebug. The meadow spittlebug is one of several species of this commonly recognized group of sap-feeding insects. Spittlebugs are familiar because of the frothy, wet mass of “spittle” that surrounds the nymphs as they feed on sap from their host plants. The spittle is produced by the immature stage of the insect (the nymph) and protects the nymphs from natural enemies and desiccation.

While the foam-like masses of spittlebugs are conspicuous and somewhat obnoxious, spittlebugs cause little harm to plants. Control efforts usually are not warranted.