Yard and Garden: Strawberries

Strawberries are the fruit of choice for home gardeners with limited space for fruit production.  Strawberries and raspberries give greater returns for the labor involved than any other fruit, and can be grown throughout Iowa with proper winter protection. Horticulture specialists with Iowa State University Extension and Outreach have answers to questions about strawberry pests and diseases. To have additional gardening questions answered, contact the specialists by calling or emailing the ISU Extension and Outreach horticulture hotline at 515-294-3108 or hortline@iastate.edu.

How do I control weeds in my strawberry patch? 

Weed control is essential to ensure optimal plant growth and fruit production. Weeds compete with the strawberry plants for water, nutrients and sunlight. Weeds also reduce air circulation, which results in fruit and foliage staying wet for longer periods. Disease problems are more serious when plant tissue remains wet for long periods of time.  

Cultivation, hand pulling and mulching are the most practical weed control measures for home gardeners. Cultivate often, but shallow, to control weeds. Destroy the weeds before they have a chance to flower and produce seeds. Clean, weed-free straw and other organic materials can be applied as a mulch between plant rows. Herbicides are not a viable option as few, if any, herbicides can be used on home strawberry plantings. 

Some of my strawberries in the garden 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 is also known as Botrytis fruit rot.  Gray mold is favored by poor air circulation and high humidity levels 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 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 the strawberry planting frequently. Pick berries as soon as they ripen. 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 regard 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. 

There are small, black, yellow-spotted beetles feeding on my strawberries. What should I do? 

The small, black beetles are likely sap beetles. They also are 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.