Fungus Gnat Management

Fungus Gnat Management

Fungus gnats (Bradysia spp.) are major insect pests of greenhouse crops and can cause economic losses across a wide range of crops during stock plant, propagation and finished plant production. Female fungus gnat adults lay eggs in growing media, and the emerging larvae feed on the roots and crown.

Fungus gnat management is an ongoing focus of our research team. The objective of the study reported here was to evaluate the efficacy of different insecticides applied as media drenches. The notable feature of this study was that we tested insecticides at several geographic locations simultaneously. We used poinsettia as a model test crop because it was grown in all the collaborating greenhouses.

Research Methods

Six-inch poinsettias were grown in eight greenhouse locations that included seven commercial growers in Colorado, Michigan, New Hampshire, New Jersey and the University of New Hampshire (UNH). Ten containers received each insecticide treatment in each location. There were a total of eight insecticides evaluated and a control that did not receive an insecticide treatment.

In the commercial greenhouses, the experimental plants, those receiving the treatments, were grown and managed alongside commercial crops. Insecticide sprays or media-applied fungicides were permitted, but no insecticide drenches were applied other than the experimental treatments. At UNH, no insecticides or fungicides were applied other than the experimental treatments.

Only one media drench application was made in the commercial greenhouses. For those insecticides labeled for multiple applications, two applications were made for several treatments at UNH (see Figure 1). Because the study was part of our Young Plant Research Center program, we were interested in fungus gnat control across a wide range of floricultural crops, rather than just poinsettia. We therefore allowed some treatments that were not labeled for poinsettia. There were two applications of Distance at UNH, although Distance should only be applied once to poinsettia, and Adept was used even though this insect growth regulator is not registered for poinsettia. In addition, DuraGuard, which is normally applied as a spray to the growing medium surface for fungus gnat control, was applied as a full-volume drench.

Insecticide applications were made on Oct. 18, 2005. For those treatments at UNH that received two applications, there was an additional drench application two weeks earlier on Oct. 4, 2005.

Twenty-four hours after the Oct. 18 application, each plant was cut off at the surface of the growing medium line using clippers, and the containers with growing media were placed in separate bags for 28 days. A yellow sticky card was placed on the surface of the growing medium. Any adult fungus gnats emerging from the growing medium were caught on the yellow sticky card and counted.

Results and Discussion

Counts in the untreated control containers varied greatly between each location, from a high of 121 fungus gnat adults emerging per container to a mean of less than one fungus gnat adult per container. This may be due to the variability in pest pressure between greenhouses. Because each adult fungus gnat female can lay up to 300 eggs, populations can rapidly increase, so it is essential to keep fungus gnat numbers low before planting and early in the crop production cycle. Some operations in the study were able to “empty out” their greenhouses before the poinsettia crop was started, which effectively eliminated any carryover pests.

Fungus gnats may be initially present on rooted cuttings or in growing media. Because fungus gnat life stages occur both above (adults) and in growing medium (larvae), both sprays and drenches of insecticides are typically required. However, the use of spray applications in dealing with fungus gnats differed among the locations.

Crop conditions varied among the locations, and fungus gnat development is favored by overwatering, high humidity and low light levels, which impact drying of the growing medium. In addition, growing media that retain high moisture and greenhouses that have soil rather than concrete floors tend to favor fungus gnat development. There are several Bradysia species of insects that we collectively call “fungus gnats,” and populations may have varied from one location to another.

Duraguard, Adept and Azatin provided moderate control. For most locations, fungus gnat adult counts were less than 50 percent when compared with the untreated containers. In several locations, however, the number of fungus gnat adults was not significantly different from the untreated (control) for all three insecticides. Note that Azatin may be more effective when applied multiple times.

The insect growth regulators Citation and Distance provided sufficient control of fungus gnats, as did Marathon and the entomopathogenic nematode product Nemasys.

Safari was consistently the most effective product and provided better control than Marathon. Both Safari and Marathon are neonicotinoid-based insecticides. Overall, fewer than five fungus gnat adults emerged from the Safari-treated containers in all greenhouses.

Figure 1 shows the complete range of treatments at UNH, including the treatments where insecticides were applied twice. Two applications of Citation, Nemasys and Distance were all effective and similar to the control provided from one application of Safari. However, it should be noted that the label specifies that only one application of Distance be applied to poinsettia, because phytotoxicity has been observed when using this insecticide on poinsettia. Label information for some of the products also included precautionary statements regarding applications to other crops such as begonia and hibiscus. Although Safari was effective in controlling fungus gnats, it should not be rotated with Marathon because Safari and Marathon have similar modes of action. In addition, Safari should only be applied as a drench once per cropping cycle in order to avoid resistance.

Results from the nematode product Nemasys (active ingredient Steinernema feltiae) were encouraging. In a separate study (organic production of poinsettia) in 2005 with poinsettia in which Nemasys was the only insecticide used, we obtained acceptable control of fungus gnats (although four applications were needed throughout the cropping cycle). Several commercially available products contain the nematode, Steinernema feltiae.

Fungus gnats are pests that can be effectively controlled using commercially available insecticides in addition to implementing practices such as sanitation and avoiding excess soil moisture. When testing any new insecticide in your rotation program, always read the label and manufacturer’s instructions. Test on a small sample of plants (around 10 to 20) before applying to the entire crop.

We were pleased with the quality of information collected by our grower collaborators, and a similar protocol might be helpful at your location. Finally, avoid using insecticides with the same mode of action (such as Marathon and Safari) in succession. Always use at least two insecticides with different modes of action in between using any neonicotinoid-based insecticide.

Leave a Reply

More From Plant Culture...
Hendriks-Half-Open-Roof_GGS

March 26, 2015

10 Greenhouse Products For First-Rate Growing Environments

From coverings to fork-lifts, greenhouse suppliers offer a variety of products to make growing easier. Check out the slideshow to learn more about these, plus several other products that can offer you value, versatility and durability.

Read More
Rose rosette on Knockout rose, April 2012. Photo credit: Alan Windham, University of Tennessee

March 25, 2015

$58 Million In APHIS Farm Bill Funding Will Support Horticulture Priorities

Nearly $58 million as been allocated by the USDA's Animal and Plant Health Inspection Service (APHIS) to support the industry's Plant Pest and Disease Management and Disaster Prevention Program, under Farm Bill Section 10007. The program will support mitigation efforts for specialty crops, including providing research and other funding to address plant pest and disease priorities for the specialty crop industry, including floriculture and nursery crops.

Read More
AFE scholarship_Ryan Dickson

March 25, 2015

AFE Educational Grant And Scholarship Application Deadlines Approaching

Apply now for American Floral Endowment (AFE) scholarships or educational grants. Applications can be found online. For educational grants for 2015-2016, applications must be submitted no later than June 1. Scholarship applications are due May 1. AFE will award $40,000 in scholarships for 2015.

Read More
Latest Stories
Bee on a Sedum

March 17, 2015

4 Key Pollinator Research Projects To Be Funded By Hort…

The Horticultural Research Institute will grant $125,000 in financial support for four key projects as part of the Horticultural Industry Bee & Pollinator Stewardship Initiative. The Initiative has three primary goals. First, to convene a task force to develop a bee and pollinator stewardship program, including creation of best management practices for plant production. Second, to identify and fund research that will help answer key science questions and fill gaps needed to design and refine the stewardship program. Third, to seek to positively position the horticultural community and its customers by collaborating with other compatible groups interested in augmenting pollinator habitat and protection.

Read More

March 11, 2015

Pollinator Initiative Promotes Bee-Friendly Talking Poi…

AmericanHort and the Society of American Florists are working tirelessly with the ornamental industry's Pollinator Stewardship Initiative on a number of new projects.

Read More

February 11, 2015

Infusion Technology Boosts Seed Performance, Study Sugg…

Seven-year-old wheat seed germination can increase by as much as 83 percent, according to a Vital Force Technology Study that looks at the effects of energy infusion technology on plant vitality.

Read More

February 3, 2015

American Floral Endowment Accepting Research Pre-Propos…

If you are pursuing a floriculture research project, now is the time to apply for funding through the American Floral Endowment. Research pre-proposal applications for 2015-2016 funding are due to AFE by June 1, 2015.

Read More

January 27, 2015

Marijuana’s Trajectory And Ascent To Horticultural Cr…

Marijuana growing is poised for change as growers and researchers focus on improving production practices.

Read More

December 9, 2014

Greenhouse Production: Two Years Of Basics & Beyond…

Greenhouse Grower's Basics & Beyond articles cover some of the latest news and research going on in greenhouse production. Here are article links for the last two years.

Read More
GrowIt! App Wins Gold At Design100 2014 US Mobile & App Design Awards

November 24, 2014

GrowIt! App Wins Gold At Design100 2014 US Mobile &…

The social garden app GrowIt! takes the Gold Winner award at the design100 2014 Mobile & App Design Awards.

Read More

November 10, 2014

The Perennial Farm Joins HGTV HOME Plant Collection

The Perennial Farm joins the HGTV HOME Plant Collection growers' network for 2015.

Read More
AmericanHort

November 4, 2014

AmericanHort Publishes Revised American Standard For Nu…

AmericanHort announces the revised American Standard for Nursery Stock (ANSI Z60.1) is now available for industry use. The Standard reflects the consensus of the industry regarding how nursery stock — living plants other than annuals — should be specified and sold within the trade.

Read More

September 26, 2014

Master The Art Of Watering

Watering is elemental to healthy plants, but one of the hardest concepts for new employees to master in the greenhouse. Recommend these tips to start them off right.

Read More

September 16, 2014

Ball FloraPlant’s Las Limas Facility Provides Gro…

Ball FloraPlant’s Las Limas farm in Esteli, Nicaragua, is one year away from full production, but sales and quality from the two-year-old facility are right on track.

Read More
Erysimum 'Cheers' from Darwin Perennials

September 15, 2014

Darwin Perennials Takes Production Offshore In Bogota, …

With its recent purchase of a farm in Colombia, Darwin Perennials is ready to amp up supply of its perennial genetics, to provide growers with tried-and-true varieties and comprehensive production specifications.

Read More

July 23, 2014

Plan Now To Prevent Bract Edge Burn On Poinsettias

Reduce fertilizer and water, and allow your poinsettias to develop slowly during the final four weeks of production to avoid bract edge burn.

Read More

July 11, 2014

Growing Your Crops Above Their Base Temperature

Lowering temperature set points in the greenhouse may help you combat rising heating costs.

Read More

May 1, 2014

Growers Report Nutritional Problems On Geraniums

In recent weeks, several growers have contacted Michigan State University Specialists about leaf discoloration on geraniums, especially the purpling of lower leaves.

Read More

April 22, 2014

How Two Postharvest Care Products Worked On Potted Plan…

What your potted plants look like at retail translates to sales or fails. North Carolina State University researchers report on how two postharvest care products performed.

Read More
Dianthus 'Passion' from Emerald Coast Growers

March 27, 2014

Growing Dianthus Successfully

Here's some advice on transplanting and producing this classic perennial favorite.

Read More
Aquilegia canadensis

March 10, 2014

Tips For Producing Aquilegia

Advice on planting, temperature, vernalization, lighting and more on columbine from Emerald Coast Growers' head grower Josiah Raymer.

Read More