How to Deal with Annoying Fungus Gnats on the Farm

darkwinged fungus gnat larvae
Darkwinged fungus gnat larvae
Photo by Whitney Cranshaw

Pest Specs

Fungus gnats are small flies that infest soil, container media, and other sources of organic decomposition. The larvae of most species feed on fungi and decaying organic matter and are not considered an economic problem. A few species will attack healthy root tissue of economic plants and can an occasional problem in greenhouses and vegetable transplant industry, where they can damage seedlings and plants. In addition, large numbers of flying gnats may be a nuisance to workers.

Identification

The larvae are slender with a black head and an elongated, whitish-to-clear legless body. Length when fully grown is about ¼ inch. If conditions are especially moist and fungus gnats are abundant, larvae can leave slime trails on the surface of media that look like trails from small slugs.

The adults are small, delicate flies with a dark-brown body and dusky wings. They have a small head as well as rounded, moderately prominent eyes that meet above the base of the antennae. The legs and wings are comparatively long. They look more like tiny mosquitoes than common flies. When disturbed, adults run rapidly or take flight, which usually consists of short darting or hovering movements over a small area.

Survival and Spread

Females lay tiny eggs in moist organic debris or in damp organic media where larvae feed and pupate. At 75°F, eggs hatch in about three days. The larvae take roughly 10 days to develop into pupae; and about four days later, the adults emerge. A generation of fungus gnats (from female to female) can be produced in about 17 days depending upon temperature. The warmer it is, the faster they will develop and the more generations will be produced in a year.

Fungus gnats have many overlapping generations each year. Studies suggest that fungi provide an essential nutrient source for the larvae. However, if fungi are in short supply, the larvae use seedling plants as an alternate food source.

Management Methods

Sound management practices can help remove the conditions necessary for the development of fungus gnats and reduce the need for pesticides.

Most of the larvae are in the top inch of soil. Rogue out any old plants and rotting materials. Fungus gnat problems are exacerbated by over-wet conditions and diseased roots, and are a symptom of poor cultural practices.

Potting media should be stored dry, and pots and production areas should be well drained. Fungus gnats can exist on soil fungi, algae under benches, and on damp mossy benches. Some growers apply hydrated lime to eliminate the fungal food source.
Insecticides are rarely warranted to control fungus gnats. If high populations become intolerable, biological controls such as Bacillus thuringiensis subspecies israelensis, predaceous mites, and/or Steinernema nematodes can be used to control the larvae. Otherwise, a pyrethroid will provide temporary, fast-acting control.

An integrated pest management approach that includes good water management, practices that promote good root health, and judicious use of insecticides will keep most fungus gnat problems under control.

Topics: ,

Leave a Reply

Fruits Stories
Citrus
September 21, 2017
Hurricane Relief Fund Launched for Florida Farmworkers
Money raised will benefit Redlands Christian Migrant Association’s efforts to aid families in need. Read More
Picking fresh Florida blueberries
Berries
September 21, 2017
Ways Florida Blueberry Growers Can Elevate Their Message
Promotional efforts seek to harness power that drives the Sunshine State's ‘little blue dynamos.’ Read More
Inside the Horticulture field tour wagon at the 2016 Florida Ag Expo
Florida Ag Expo
September 21, 2017
Everything You Need to Know About the 2017 Florida Ag Expo
More education choices, flexible field tours, and networking opportunities to provide an enhanced attendee experience. Read More
Bacterial wilt symptoms on blueberry leaves
Berries
September 20, 2017
Getting to the Bottom of Bacterial Wilt in Blueberries
Prolific plant pathogen now presenting a new challenge for Florida producers and researchers. Read More
Citrus
September 19, 2017
Precision in Specialty Crops Gains Momentum
Here are some of the key drivers that may transform your farm in the years ahead. Read More
Fruits
September 19, 2017
EPA Mulls Restricting Dicamba Use
Proposal is a part of agency’s focus on reducing herbicide injury in vulnerable crops. Read More
Fruits
September 19, 2017
Washington State University Creates BMSB Management Resource Page
As populations grow in the state, university offers growers pest management advice. Read More
Berries
September 19, 2017
UC Davis Strawberry Lawuit Settled
Former university breeders to return any crosses that used unpatented varieties and agree the school owns rights to them. Read More
Neo 1 hops at UF/IFAS MREC
Citrus
September 19, 2017
Hopes High for Hops Fresh From Florida
When it comes to alternative crop solutions, something good is brewing in the Sunshine State. Do you have what it takes to tap in? Read More
Apples & Pears
September 16, 2017
Researcher Finds Bacteria Can Stop Blue Mold on Apples
The natural bacterium found in soil can survive in cold storage; this promising biocontrol offers an alternative to chemical treatments. Read More
Laurel wilt-damaged avocado tree leaves
Disease Control
September 15, 2017
Scientist Uncovers Chilling Side of Deadly Avocado Disease
Lab tests indicate laurel wilt pathogen grows faster in the fall and winter. Read More
Winter melon damage from Hurricane Irma in Elkton, FL
Citrus
September 15, 2017
Help Extended to Hurricane-Weary Farmers Dealing With Disaster
USDA chief grants extra time and special procedures to document and file claims. Read More
raindrops in standing water
Citrus
September 13, 2017
New Guidance on FSMA Ag Water Compliance, Water Testing, and Farm Inspections Announced
FDA issued a rule to extend compliance dates for agricultural water and announced a start date for farm inspections. Read More
Packinghouse damage from Irma at SWFREC in Immokalee
Citrus
September 13, 2017
Florida Farmers Digging out From Impacts of Irma
Damage reports starting to flood in from the field following monster storm, and it's not pretty. Read More
Berries
September 12, 2017
Longtime American Fruit Grower Columnist Charlie O’Dell Dies
“The Ole Crow,” as he called himself, passed away unexpectedly at home in Virginia at the age of 82. Read More
The Latest
Citrus
September 22, 2017
Water Management Concerns Flowing in Flo…
Efforts mounted and executed to move gallons by the ton to protect property. Read More
Citrus
September 22, 2017
When it Comes to Growing, Florida Farmer…
Let's raise a toast to the bold producers and researchers who are taking our industry beyond previously perceived crop viability boundaries to places once figured forbidden. Read More
Citrus
September 21, 2017
Hurricane Relief Fund Launched for Flori…
Money raised will benefit Redlands Christian Migrant Association’s efforts to aid families in need. Read More
Florida Ag Expo
September 21, 2017
Everything You Need to Know About the 20…
More education choices, flexible field tours, and networking opportunities to provide an enhanced attendee experience. Read More
Citrus
September 19, 2017
Precision in Specialty Crops Gains Momen…
Here are some of the key drivers that may transform your farm in the years ahead. Read More
Fruits
September 19, 2017
EPA Mulls Restricting Dicamba Use
Proposal is a part of agency’s focus on reducing herbicide injury in vulnerable crops. Read More
Fruits
September 19, 2017
Washington State University Creates BMSB…
As populations grow in the state, university offers growers pest management advice. Read More
Citrus
September 19, 2017
Hopes High for Hops Fresh From Florida
When it comes to alternative crop solutions, something good is brewing in the Sunshine State. Do you have what it takes to tap in? Read More
Disease Control
September 15, 2017
Scientist Uncovers Chilling Side of Dead…
Lab tests indicate laurel wilt pathogen grows faster in the fall and winter. Read More
Citrus
September 15, 2017
Help Extended to Hurricane-Weary Farmers…
USDA chief grants extra time and special procedures to document and file claims. Read More
Citrus
September 13, 2017
New Guidance on FSMA Ag Water Compliance…
FDA issued a rule to extend compliance dates for agricultural water and announced a start date for farm inspections. Read More
Citrus
September 13, 2017
Florida Farmers Digging out From Impacts…
Damage reports starting to flood in from the field following monster storm, and it's not pretty. Read More
Farm Management
September 10, 2017
$3 Million Available to Train Future Agr…
There are a lot more jobs being created than there are graduates with bachelor’s or higher degrees who can fill them. Read More
Citrus
September 7, 2017
Summer News Stories that Have Growers Ta…
Farming has been in the media spotlight this year. I asked each of this month’s columnists and contributors for their Read More
Citrus
September 7, 2017
Whose Sustainable Standard Wins?
Retailers’ race to win the most sustainable produce prize leaves growers trying to keep up with fast-developing demands. Read More
Citrus
September 7, 2017
Improving Water Management: Can Silicon …
Though very much-needed, technological solutions must be cost-effective and industry appropriate. Read More
Fruits
September 5, 2017
Organic Fruit Sales Surge 12%
Organic vegetable sales rose 6%, as consumer demand is still going strong. Read More
Fruits
September 3, 2017
California Table Olive Forecast Up 9%
Like many other Golden State growers, olive farmers benefitted from a wet winter, but concerns remain over recent hot weather. Read More