Greenhouse - Shorefly and Fungus Gnat Control

The following is information on shore fly and fungus gnat control in the greenhouse.

Shorefly and Fungus Gnats

The populations of shoreflies and fungus gnats will be exploding after the extended cloud cover and rainy periods. Fungus gnats are best controlled in the larval stage by applying drenches or heavy sprays. Biorational products applied as soil drenches include azadirachtin (Azatin), Bacillus thuringiensis H-14 (Gnatrol), cyromazine (Citation), fenoxycarb (Precision), kinoprene (Enstar II) and diflubenzuron (Adept). Biological controls are insect-attacking nematodes (mostly Steinernema feltiae) and predatory mites in the genus Hypoaspis. The insect growth regulators Citation, Precision and Adept) are registered for larval control of shore fly, but results may be inconsistent. This is probably because shore flies live in very wet areas and do not feed on plant roots. Insecticidal soap will give knockdown of adult shoreflies. Cultural and physical controls will help, but in wet seasons like the spring of 2009 this is nearly impossible. Avoid potting mixes that promote the growth of algae and keep plants on the dry side. Clean algae from benches, walls and floors. Avoid letting areas stay permanently wet in the greenhouse. Some growers have applied hydrated lime under the benches to discourage growth of algae. If you are growing on the floor you are out of luck with this practice.

Reprinted from the May 15, 2009 edition of the Greenhouse TPM/IPM Bi-Weekly Report from the University of Maryland Cooperative Extension, Central Maryland Research and Education Center