PPDL Picture of the Week for

June 15, 2015

Strawberry Problems

Bruce Bordelon, Professor, Department of Horticulture and Landscape Architecture

Strawberry harvest is underway across the state and lots of folks are enjoying the fruits of their labor. Strawberries are among the most popular fruit to grow in the home garden. They take up little space, produce fruit one year after planting, and provide a generous supply of tasty berries for a month or more. However, anyone who has tried knows that it is difficult to grow berries in a backyard situation that are as perfect as what we find in the grocery store. Some of the most common problems of locally grown berries are damaging pests and diseases. Of particular concern during harvest are slugs, sap beetles, and Botrytis gray mold. A quick look through my row of berries at the Meigs Horticulture Research Farm found at least two of these culprits. 

Botrytis gray mold is a diseased caused by the fungal pathogen Botrytis cinerea. Botrytis is a common saprophyte and pathogen of a number of fruit and ornamental crops. In strawberries, the fungus invades during bloom and usually infects the dying petals or stamens. The fungus remains latent until the fruit begins to ripen then progresses into the ripening berry to cause a rot. You often find infections starting at the top of the berry near the cap, where the dying flower parts remain. (Picture 1.)

Sap beetles (Stelidota geminata), are another common pests of strawberries. The adult beetles invade the plantings as the fruit ripens and feed on berries, leaving deep cavities and tunnels. This damage often leads to development of secondary rots (Picture 2). The adult beetles are small, about 1/8 inch long, oval, and mottled brown in color (Picture 3). They are difficult to see because they usually drop to ground when disturbed. Growers are often surprised by the size of the cavities considering the small size of the beetles (Figure 4). We often hear complaints of bird pecking, but I suspect most of the damage we see is from sap beetles, not birds. 

Picnic beetles (Glischrochilus species) are another potential pest of strawberries, though they are more commonly found on raspberries. They are, however, opportunists and can be found feeding on strawberries as well. The adults are larger than sap beetles, about ¼ inch long, dark in color, usually with four orange spots on the back. One distinguishing characteristic is that they have knobbed antennae  (Picture 4.) 
Slugs (Deroceras species) are molluscs, not insects. But they cause damage to strawberries that resembles damage from sap beetles. They chew deep holes in the surface of the berries, especially under the cap. Those found is strawberries are usually small, less than one inch long, though certain specimens can be much larger. 

Control: Sanitation is the key to managing pests and diseases in the home strawberry planting. Since beetles are attracted to overripe fruit, pick often and discard all damaged fruit away from the planting. Keep berries from direct contact with soil by maintaining a layer of mulch. Keep rows narrow to allow the surface to dry. Use of insecticides for sap beetles and slugs is not recommended due to the frequent harvests. For Botrytis, if fungicides are considered, they should be applied during bloom when infections are likely to occur. Application near harvest is not effective at controlling the disease. 

More information about strawberry pests can be found in ID-146 Managing Pests in the Home Fruit Planting. https://www.extension.purdue.edu/extmedia/id/id-146-w.pdf​

​Click image to enlarge

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Picture 1: Botrytis gray mold on strawberry.
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Picture 2: Sap beetle damage and resulting rot.
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Picture 3: Sap beetle adults on berry.  
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Picture 4: Large cavities eaten by strawberry sap beetles.
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Picture 5: Picnic beetle fleeing the scene of the crime. Note the sporulation from gray mold beginning to develop on the sunken lesion, and the dead stamen on the cap near where the infection started.  ​