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How to Manage Pests
UC Pest Management Guidelines
Floriculture and Ornamental Nurseries
Fungus Gnats
Scientific names: Bradysia coprophila, Bradysia impatien
(Reviewed 1/04,
updated 1/04)
In this Guideline:
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DESCRIPTION OF THE PESTS
Fungus gnats are small (2-5 mm long) mosquitolike flies with dark wings,
delicate legs, and long antennae. They lay their eggs in soil, and the eggs
hatch about 4 days later. There are four larval instars that increase in size
up to about 0.33 inch (8 mm). Larvae
are clear, with visible internal organs, and have shiny black head capsules.
Initially larvae feed on root hairs and algae; later, larvae may feed on the
insides of roots. When populations are high, larvae may bore into larger roots
or stems that are in the soil. Larvae will also feed on leaves touching the
soil. One generation may complete development in 21 (72°F) to 40
(61°F) days.
DAMAGE
Larvae usually feed on roots and algae within 1 inch of the soil surface. Root
feeding by larvae can allow entry of plant pathogens. Direct damage through
root feeding can cause wilting even though the plants are being sufficiently
watered. Damage is particularly severe in propagation areas, in seedling flats,
and with especially sensitive crops. Adult fungus gnats also disseminate
soil-inhabiting pathogens on their bodies and in their feces. Fungus gnat
adults can be a nuisance when present in large numbers.
BIOLOGICAL CONTROL
Biological control agents include nematodes (Steinernema feltiae),
soil-inhabiting predaceous mites
(Hypoaspis miles), and the bacteria Bacillus thuringiensis
(Gnatrol).
CULTURAL CONTROL
Keep production areas free of weeds and algal scum, which can serve as breeding
sites for fungus gnat populations. Maintaining overwatered conditions and using
either incompletely composted organic matter or manure in potting media
provides ideal conditions for fungus gnats. Commercial sources of peat may be
infested with fungus gnats and should be steamed before use when growing crops
sensitive to fungus gnats. Use hydrated lime under benches to control algal
growth and thus reduce populations of fungus gnats.
MONITORING and WHEN TO TREAT
Yellow sticky cards placed in
greenhouses will capture adult fungus gnats. Small emergence traps can also be
used to determine precisely where adults are emerging. Larval populations can
be monitored with cubes or slices of potatoes pressed just into the soil.
Pyrethroids are useful for knocking down adult populations and
microencapsulated pesticides (pyriproxyfen and chlorpyrifos both are available
in microencapsulated formulations) applied to the soil are effective against
larvae.
Apply drenches to top 1 inch of soil to kill larvae and use foggers, aerosols,
or sprays to control adults.
TREATMENT
Selected Materials Registered for Use on Greenhouse or Nursery Ornamentals
Read and follow the instructions on the label before using any pesticide.
Before using a pesticide for the first time or on a new crop or cultivar, treat
a few plants and check for phytotoxicity.
| Class |
|
Pesticide (commercial name) |
Manufacturer |
R.E.I.1 |
Comments |
| biological |
A. |
Bacillus thuringiensis (Gnatrol) |
Valent |
4 |
Do not apply with fertilizers or fungicides containing copper
or chlorine. Not effective on shore flies. |
| botanical |
A. |
pyrethrin/PBO2 (PT 1100) (Pyrethrum TR) |
Whitmire MicroGen |
12 |
An aerosol. Also effective against adults.
|
| B. |
pyrethrin/rotenone (Pyrellin EC) |
Webb Wright |
12 |
Also effective against adults. |
| insect growth regulator |
A. |
azadirachtin (Azatin XL Plus)
|
Olympic
|
4
|
Must contact insect. Repeated applications necessary. Only
effective on larvae. Label permits low-volume application. |
| B. |
azadirachtin
(Ornazin 3%EC) |
SePRO |
12 |
Do not exceed 22.5 oz/acre/application |
| C. |
cyromazine (Citation 75 WP) |
Syngenta |
12 |
Certification training required to use this product. Also
effective against shorefly larvae. |
| D. |
diflubenzuron (Adept 25WP) |
Uniroyal |
12 |
Apply as spray or drench to top 2 inches of soil. |
| E. |
pyriproxyfen (Distance) |
Valent |
12 |
Do not apply more than 2 times per cropping cycle or per 6
months. Do not apply through any type of irrigation system. |
| F. |
s-kinoprene (Enstar II) |
Wellmark |
4 |
Apply prebloom. Also labeled for low volume use. Do not apply
through any type of irrigation system. |
| neonicotinoid |
A. |
imidacloprid (Marathon 1G)
|
Olympic |
12 |
Not to be used more than once every 16 weeks. Alternate with
insecticides that have a different mode of action to prevent development of
resistance to neonicotinoids. Do not apply to soils that are water logged or
saturated. Do not apply to bedding plants intended to be used as food crops.
Thrips suppression only. |
| B. |
imidacloprid (Marathon 60 WP) |
Olympic |
12 |
As above. Apply only as a drench. |
| organophosphate |
A. |
acephate (Address) |
Dow |
24 |
Do not use through any type of irrigation system. |
| B. |
acephate (Orthene T, T&O Spray) 75WP |
Valent |
24 |
A number of chrysanthemum varieties have exhibited phytotoxic
reactions. In greenhouses only labeled for use on anthurium, cacti, carnation,
rose, orchids, some foliage plants, young poinsettia, and some varieties of
chrysanthemum. Can stunt new growth in roses. Do not use through any type of
irrigation system. |
| C. |
acephate (PT 1300 Orthene TR) |
Whitmire MicroGen |
24 |
An aerosol for greenhouse use only. |
| D. |
chlorpyrifos* (PT DuraGuard ME) |
Whitmire MicroGen |
24 |
|
| pyrethroid |
A. |
bifenthrin* (Attain TR) |
Whitmire MicroGen |
12 |
Check label. A fogger for greenhouse use only. |
| B. |
bifenthrin* (Talstar Flowable) |
FMC |
12 |
Also effective against adults. Label permits low-volume application. |
| C. |
cyfluthrin (Decathlon 20 WP) |
Olympic |
12 |
Also effective against adults. Label permits low-volume
application. Do not use through any type of irrigation system. |
| D.
|
deltamethrin* (DeltaGard) |
Bayer |
12 |
Do not use through any type of irrigation system. |
| E. |
fenpropathrin* (Tame 2.4 EC Spray) |
Valent |
24 |
Also effective against adults. Label permits low-volume
application. Do not use through any type of irrigation system. |
| F. |
fluvalinate Mavrik Aquaflow |
Wellmark |
12 |
Also effective against adults. Label permits low-volume
application. Also labeled as a cutting dip at 5 fl oz/100 gal. Do not use
through any type of irrigation system. |
| G. |
permethrin* (Astro) |
FMC |
12 |
Direct application to blooms may cause browning of petals.
Marginal leaf burn may occur on salvia, diffenbachia, and pteris fern. Label
permits low-volume application. Do not apply more than 2 lb
a.i./acre/year. |
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UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Insects and Mites
K. L. Robb, UC Cooperative Extension, San Diego Co.
H. S. Costa, Entomology, UC Riverside
J. A. Bethke, Entomology, UC Riverside
M. P. Parrella, Entomology, UC Davis
Acknowledgment for contributions to the insects and mites section:
R. S. Cowles, Connecticut Agricultural Experiment Station, Windsor, CT
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