In the strawberry benchtop system in the greenhouses at Southwest Purdue Ag Center (SWPAC), we have been experiencing infestations in red berries of a small, clear larvae with a black head capsule. The larvae are often found in clusters on a single fruit and were difficult for us to identify. We encountered them in early spring, when there were not a lot of fruits present and the temperatures were still quite cold (that didn’t seem to impact the pest). After several attempts to raise them on berries we were successful! The culprit has been identified as larvae of the dark-winged fungus gnat (Family: Sciaridae; Fig. 1).
Figure 1: Dark-winged fungus gnat larvae on ripe strawberry. Photo by John Obermeyer.
They are found only on red berries and only when the berries are in contact with the growing medium. Fungus gnats feed on decaying matter in the soil and plant roots. They are often a problem in greenhouse production systems, mainly a nuisance pest. They thrive in moist soil conditions. The observations at SWPAC are the first that we have seen them attacking healthy, and in this case ripe, fruits. You can manage this pest by managing soil moisture, allowing pots to dry out. In hydroponic or soil systems incorporating entomopathogenic nematodes (EPN), nematodes that feed on insects, is an effective way to suppress this population. Preventing the developing fruits from contacting the growing media will also prevent their spread onto the fruit. You can monitor for the presence of the adult flies by placing yellow sticky cards perpendicular to the growing media. As the adults emerge from the media they will get stuck on the cards. As always, sanitation is another key step in minimizing this pest. Cull any dying / dead plants and old soil that’s sitting around as this can serve as a residue for the pest. If you suspect fungus gnat damage in your crop, please contact Laura Ingwell (lingwell@purdue.edu).