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The soil-dwelling laelapid mite Hypoaspis miles.

Nematodes. Several entomopatho-genic (insect-pathogenic) nematodes occur naturally in the soil and parasitize a variety of soil-inhabiting insects, including fungus gnat larvae. Nematodes are small,long,slender roundworms.They are about 1/64 inch (0.5 mm) long, transparent, and practically invisible to the naked eye.They require moist soil to survive.When they find an insect, they enter it through natural openings and release a bacterium that kills the host within 48 hours.The bacterium itself serves as a partial food source for the nematodes, which complete their development inside the dead insect.The next generation of nematodes leaves the insect in search of new hosts. Unlike plant parasitic nematodes, these nematodes have no mouthparts and do no damage to plants.

Fungus gnats and shore flies ^

Several species of entomopathogenic nematodes, including Steinernema feltiae (=Neoaplectana bibionis), S. car-pocapsae, S. riobravis, and Heterorhabditis spp.are sold commercially for biological control of fungus gnats. H.megadis is sold in Europe for fungus gnat control. The mermithid Tetradonemaplicans can control fungus gnats, but it is not available commercially.These nematodes are harmless to people, animals, beneficial above-ground insects, and earthworms.

Possibilities for effective biological control

You can control fungus gnats easily by using biological methods and good sanitation practices. Shore flies are more difficult to control with biological methods.

The biological insecticide Bti controls fungus gnats but is not effective against shore flies. A commercial formulation of this bacterium, Gnatrol, is registered for the control of fungus gnats on ornamentals. Because Bt does not persist in the soil, it must be applied whenever pest populations develop. Applications as a soil drench once per week for 3 weeks are recommended. Potting medium, soluble salts, soil temperature, moisture, and pH,can all influence the effectiveness of Bt in greenhouses.

Nematodes can also be applied to crops in large quantities as a biological insecticide. Several species and isolates of nematodes are marketed under various trade names, but not all are equally effective against fungus gnat larvae. Check the label or contact the supplier to confirm that the product is effective against these pests.They should be applied to moist, but not saturated, soil. The area to be treated should be watered before and after application. The soil temperature must be above 50°F for nematodes to be effective. Application in the early evening or the morning is recommended to avoid exposing the nematodes to extreme heat and sunlight. Nematodes are applied as a spray or a drench on the soil surface. Since they can withstand pressures up to 300 psi, nematodes can be applied with the same equipment used for the application of chemical

Enemies egg -larva- pupa adult

Hypoaspis Bt var. israelensis Nematodes pesticides and through irrigation or injector systems. Always check that the nematodes are alive before applying them. Examine a drop of the dilute spray with a magnifying glass.The nematodes should be squirming. Inactive nematodes bent at sharp angles are usually dead. Nematodes are most effective at soil temperatures of 65°-85°F.They should be applied weekly for 4-8 weeks.

Although both Bti and nematodes can be effective against fungus gnats, their control may not always be satisfactory to the grower.

For long-term control, the soil-inhabiting predatory mite Hypoaspis miles, introduced early in the crop cycle, can maintain fungus gnat populations at acceptable levels.These mites are most effective when released before fungus gnat populations are established. H.miles seems to thrive in the top 1-2 inches of the growing medium and in moist areas where fungus gnats breed. Excellent control of fungus gnats has been achieved with experimental releases on poinsettia and bedding plants.This mite also works well in combination with nematodes or Bti. Commercially produced mites are shipped in vermicu-lite, bran, peat, or a similar carrier. Sprinkle the mite mixture over flats, trays, capillary mats, and floors. Shake the container occasionally to keep the mites evenly distributed throughout the container. For potted plants, !/4 teaspoon of the mite mixture sprinkled around the roots of every second pot, is recommended. Release rates vary by crop and pest populations, from 10,000-20,000 per acre for greenhouse vegetables to 10-50 per ft2 for bedding plants.Additional releases will be necessary to maintain control if pots are removed and replaced regularly. Researchers are investigating the possibility of inundating propagation beds with excessive numbers of mites so that they will be distributed to individual pots.

Alternative control methods

Sanitation

The elimination of breeding areas will reduce fungus gnat and shore fly problems quickly. Drain wet areas and repair drip irrigation systems to remove standing water and algae where flies can breed. Dispose of or sterilize infested growing media so that emerging flies will not reinfest new plantings. Remove all used potting medium and plant debris from the greenhouse as this is a place where fungus gnats can pupate.

Cultural control

Avoid overwatering plants as this allows growing media to remain saturated and promotes the growth of algae which provides an ideal environment for fungus gnat and shore fly growth and development.

Choose the correct planting medium. Although soilless root media are considered excellent for plant growth, they are also ideal for the growth and development of fungus gnats and shore flies. In a test of several different media, the fewest adult pests emerged from media containing pine bark or no bark,while the most came from media containing some hardwood bark. Potting media may also influence nematode effectiveness.

Avoid over-fertilizing plants. Excess fertilizer promotes algae growth where fungus gnats and shore flies can breed.

Chemical control

Several insect growth regulators, such as diflubenzuron,cyromazine and fenoxycarb,are registered for use on ornamentals to control fungus gnat and shore fly.These insecticides should be applied as a drench when fungus gnats or shore flies are first observed.The drenches will not harm natural enemies but may damage some types of plants. Read the label carefully for phytotoxicity information.

Horticultural oils are registered for use against fungus gnats on some greenhouse crops. Several other synthetic insecticides are available for the control of fungus gnats or shore flies, but most are very toxic to beneficial insects.

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