Minimize moisture under the benches to reduce breeding of fungus gnats there. Ample moisture favors development of fungus gnat larvae. However, existing larvae may attack plant roots if pots are under watered. Depending on level of fungus gnats, apply either a pesticide or biocontrol under benches to minimize fungus gnat numbers prior to starting crop. High numbers of fungus gnat larvae can cause serious damage to plant roots. Shore fly larvae feed only on algae and can breed in standing water. It is important to be able to distinguish between the two insects for control purposes.
Fungus gnat adults are delicate black insects usually less than 1/8 inch long, with long legs and antennae. Their wings are clear, and have a distinctive Y-shaped vein that distinguishes them from shoreflies (both are about the size of fruit flies). Fungus gnat larvae are slender with clear bodies and a black head capsule.
Shore fly adults are more stout and usually larger than fungus gnat adults. They have short legs and antennae, and dark wings with clear spots on each wing. Larvae are yellowish-brown, maggot-shaped, and do not have a distinct head capsule. Larvae of both shore flies and fungus gnats are found in the surface of the growing medium.
Yellow Sticky Cards: Count fungus gnat and shorefly adults weekly on yellow sticky cards. Place some horizontally a little above soil level; others, vertically at the plant canopy level. Examine sticky cards weekly and renew them every 1-4 weeks. Your time is an important factor in choosing the number of cards that will be monitored. A few cards counted per week is infinitely better than none at all. However, fungus gnat and shorefly populations vary considerably from place to place in the greenhouse, so place them thoughtfully.
Potato Slice Inspections: You can monitor the relative number of fungus gnat larvae in the soil by placing a disk of raw potato on the soil surface.
After 7 days, turn the disk over and count the number of fungus gnat larvae. Mary Harris used this technique to study fungus gnats and their control at the University of Georgia. You can assess whether a control measure has killed fungus gnats by comparing larval numbers before and after treatment. Make disks of thesame diameter by punching them out of potato slices with a cork borer or sharpened piece of pipe. Place 10 disks per 1000 square feet of growing area.
IPM Laboratories, Inc. warrants that the biological controls you receive will be alive and healthy when received and will contain the correct number of the species you ordered. However, as with any pest control measure, success cannot be guaranteed. IPM Laboratories, Inc. makes no guarantee, express or implied, as to the effectiveness of these products.
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