Pest description and crop damage Larvae are small white, legless maggots with black head capsules. Adult midges are delicate, black-bodied insects with long legs and antennae. Their wings have a y-shaped vein along its edge distinguishing them from shore flies which are stout-bodied with short antennae and five white spots on their dark wings. The maggots can feed on decaying organic matter as well as plant roots. Larval feeding causes damage to seedling roots and high populations can kill young plants. Both larvae and adults can move spores of plant pathogens.
Biology and life history Eggs are laid in the container substrate or greenhouse floor. The tiny eggs hatch in 4 to 6 days, larvae feed for another 2 to 14 days, then pupate in the substrate or ground for another 5 to 6 days before emerging as an adult. Adults can live a week to 10 days. There are multiple generations per year. Higher populations are associated with wet, low drainage areas of production. Increasing drainage and maintaining a moss and algae free production area will reduce conducive conditions.
Scouting and thresholds Scouting for fungus gnats is usually done with yellow sticky cards. This will give one an indication of the numbers of adult fungus gnats. Some people place potato slices on the soil or medium to monitor for the larvae. Check roots of puny-looking plants for signs of the larvae.
Management-biological control (larvae)
Natural enemies include:
- parasitic nematode (Steinernema feltiae)- Commercially available. Applied as a drench to substrate. Generally will need to be applied more than once.
- predatory mite (Stratiolaelaps)-Commercially available.
- rove beetle (Atheta coriaria)-Commercially available.
- soil-dwelling mite (Hypoaspis miles)- Applied to substrate.
Use yellow sticky traps to assess infestation and control efforts. Often, fungus gnats are a serious pest in propagation facilities, where larvae damage young roots. Infestations are associated with a highly organic potting mix. Much of the management is directed at controlling the larval stages in the media and floor. Adult control is generally less effective in controlling populations.
- acephate (Orthene TR) at 0.024 lb ai/1,000 sq ft broadcast (0.6 oz). REI 24 hr.
- acetamiprid (Tristar 30SG) at 0.5 lb ai/100 gal (2.7 oz). REI 12 hr.
- azadirachtin (Azahar, Azatin XL)-Insect growth regulator.
- Bacillus thuringiensis israelensis (Bti) (Gnatrol) as a drench to the substrate to kill larvae. Use a Bt formulation specifically designed for fungus gnats. Generally will need to be applied more than once. Some formulations are OMRI-listed for organic use.
- Beauveria bassania (Xpectro OD) up to 2 quarts per 100 gal spray volume
- beta-cyfluthrin (Tempo Ultra GC) at 45-160 ml/100 gal water
- bifenthrin (Talstar) at 0.168 to 0.335 lb ai/1,000 sq ft. REI 12 hr . REI 12 hr. Restricted use pesticide.
- canola oil (Mighty)-Do not apply more than 2.5 gal per 100 sq ft. Do not reapply within 3 days.
- chlorfenapyr (Pylon) at 0.08 to 0.16 lb ai/100 gal. REI 12 hr.
- chlorpyrifos (Duraguard ME) ) at 0.5 fl oz/gal water for heavy infestation; 0.25 fl oz/gal for preventative and maintenance .
- cinnamaldehyde (Seican)-Rates differ for appearance and pest pressure.
- cyfluthrin (Decathlon) at 1.3 oz/100 gal. REI 12 hr.
- cyfluthrin/imidacloprid (Discus N/G) at 0.063 lb ai/100 gal foliar; 0.009 to 0.014 lb ai/1,000 ft soil. REI 12 hr.
- cyromazine (Citation) at 2 oz ai/100 gal. REI 12 hr. Apply to the larval stage.
- deltamethrin (Annihilator Polyzone) at 0.25 to 1.5 fl oz per 1,000 sq ft of surfaces.
- diflubenzuron (Adept) at 0.5 oz ai/100 gal soil. REI 12 hr. Apply to the larval stage.
- dinotefuan (Safari 20SG) at 0.1 to 0.2 lb ai/1,000 ft sq; 0.05 to 0.1 lb ai/100 gal. REI 12 hr.
- esfenvalerate (Onslaught Fastcap) at 0.5 to 1.0 fl oz/gal depending on infestation, apply as wet coarse spray.
- geraniol, rosemary and peppermint oils (Keyplex Ecotrol Plus) Keyplex Ecotrol Plus)-Topical mixed at 20 to 40 fl oz/gal.
- imidacloprid (Marathon II) at 0.027 oz ai /100 gal foliar. REI 12 hr. Drench and irrigation permitted.
- Isaria fumosorosea (No-Fly WP)-Variable application rates based on application type and infestation intensity.
- mineral oil/petroleum distillate (Biocover LS)-Some formulations are OMRI-listed for organic use.
- neem oil (Rango) at 0.625 to 1.8% v/v rate, max 3 quarts/acre every 7 to 10 days.
- permethrins (Lynx EC 1.4) at 16 to 32 oz with 30 gal water in conventional hydraulic sprayer pyrethrins/canola oil (E.B. Stone, Earth-tone, Worryfree)-Adult control.
- pyrethrum/piperonyl butoxide-Adult control.
- pyriproxyfen (Distance) at 0.054 to 0.081 lb ai/100 gal (8 to 12 fl oz) foliar. REI 12 hr.
- s-kinoprene (Enstar AQ) at 0.012 to 0.024 lb ai/10,000 sq ft. REI 4 hr.
- soybean oil (Golden Pest Spray)-Some formulations are OMRI-listed for organic use.
- thiamethoxam (Flagship 25WG)-Separate application rate recommendations depend on application type.