Vol. 1, Issue 7 (May 2001)

This page brought to you with the co-operation of the Alberta Research Council and Alberta Agriculture, Food & Rural Development.

 Shore Fly

The shorefly (Scatella stagnalis) population is increasing steadily. At this time, adult shoreflies may become a nuisance to customers at retail greenhouses. They may also leave blackish residue on the leaves and flowers. They develop in the same wet conditions that attract fungus gnats.

The life cycle of shoreflies depends very much on temperature. The time to complete a cycle (from an egg to adult fly) ranges between 12 to 20 days. Damp conditions encourage shorefly development. Adults lay approximately 15 eggs per day continuously for up to 21 days on or near algae. The larvae feed on algae and may spread Pythium root disease.

Identification

Shoreflies are small dark flies that resemble a housefly. The larva is opaque and has no black head capsule, as do fungus gnats. Shoreflies have very short antennae. The five distinctive whitish spots on dark wings easily identify the adults.

Monitoring

Monitor incoming plant material for larvae and adults. Adults will easily be caught on yellow sticky cards.

Control

Good sanitation practices are important for shorefly management. Remove all possible sources of algae in the greenhouse. Use algaecides such as hydrogen peroxide to control algae. An application of hot lime on the ground works just as well as hydrogen peroxide but it also lasts longer.

Chemical control is either aimed at the immature stages or the adults. Targeting the eggs and larvae gives the best long-term control. However, it may take some time before the number of adults is reduced. Quick knock down of adults can be achieved with labeled aerosols or sprays containing pyrethrin. Dimilin® and Citation® are insect growth regulators registered for shorefly control. These will not control the adult stage of the fly.

The mention of a commercial product does not constitute an endorsement or recommendation by Alberta Agriculture, Food & Rural Development or the Alberta Research Council.