Yard and Garden: Strawberries

AMES, Iowa — Fresh strawberries, a favorite of almost everyone, are relatively easy to grow and hardy throughout Iowa. Horticulturists with Iowa State University Extension and Outreach share cultural practices to reduce damage and losses caused by insects and diseases. Gardeners with additional questions may contact the ISU Hortline, hortline@iastate.edu or 515-294-3108.

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 rather disgusting, spittlebugs cause little harm to plants. Control efforts are usually not warranted. 

Some of the strawberries in my 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 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 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 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. 

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.