Review pt 1:Fungus Gnats
Although fungus gnats (Sciaridae) are primarily seen as a nuisance in indoor
production spaces, they are responsible for a lot more than that! As a result of their favourite food source (plant roots), these pests are capable of acquiring and spreading fungal disease amongst the crop.
The following information is a summary of session 5 of the BugBites
Series: Fungus Gnats and Shorefly Suppression with Beneficial Organisms. To
watch the full session, click here!
Pest
Description:
Adult fungus gnats are mosquito-like insects
with long legs, and a characteristic y-shaped wing vein. Adults can be found
hanging around or near the soil, mostly under plant canopy. The fungus gnat
larvae are white with a shiny black head. Larvae spend most of their time
underground and will feed on the roots.
Figure 1. A photo of an adult fungus gnat stuck to a yellow sticky card. Below, is an image of the fungus gnat larvae. If you look closely, you can see the characteristic black head at the end of the larva. Image taken from the BugBites! Session 5 presentation.
Monitoring
and Scouting:
Adults are not strong fliers, meaning that
sticky cards will only be effective when placed close to the soil line. If
placed correctly, traditional sticky cards are a great tool to monitor population
sizes.
As
an attractant, some growers will use half a potato, or a potato slice, placed
in a pot to draw larvae up from the soil. As the larvae are accustomed to
feeding on roots, the use of a tuber is a big draw.
For
the adults there are various traps available. These traps typically involve the
use of an attractant (ex. UV bulb) and a way to capture the insects (sticky
cards, soapy water solution etc.). This is useful for general scouting purposes
as well as mass trapping.
Biological Control Options:
As with any biological control program, prevention is the first line of defense
in controlling population sizes. By conducting regular scouting checks of the
crop, and maintaining populations of biological control agents, you can limit
the degree of pest infestation.
Dalotia coriaria;
Rove beetle
- Predator
to both shoreflies and fungus gnats
- Both
adults and larvae are predators
- Orange
larvae will be noticeable in your soil
- Adults
readily move around via flight
- Establish readily in greenhouses and work well in hydroponic systems
Figure 2. A photo of a rove beetle in the adult (left) and larval (right) stages. stuck to a yellow sticky card. Image taken from the BugBites! Session 5 presentation
The
use of rearing boxes allows for a slow-release approach and will help maintain
beetle populations through the season. Rearing boxes can be as basic as media
(ex. peat, vermiculite) set inside a Tupperware container, and supplemented
with food (ex dog or fish food, artemia). It is crucial to keep this moist, but
not wet. These can be placed under benches.
Bacillus thuringeniensis israeleinsis
- Functions
as a stomach toxin for fungus gnats
- Best applied via soil drench or chemigation.
Irrigation is not ideal as the soil needs to get very wet to allow for good
establishment of the biopesticide
Stratiolaelaps scimitus; predatory mite
- Target
fungus gnat larvae
- Well suited for greenhouse environments: optimum development temperature of 25oC (77oF)
- Ideal range is 15-30oC (59-86oF)
- Live in the top half inch of the soil: best applied to the substrate surface after transplant
- Want
to avoid burying too deep in the growing media
- Does
not establish well in rockwool
- Persistent control agents, and can provide season-long
protection
Figure 3. An image of an adult predatory mite. Image taken from the BugBites! Session 5 presentation
S. scimitus can be mixed with Dalotia, but it is not recommended
to introduce them before adding into the crop. They will feed on each other, so
make sure they are spread evenly throughout the canopy when distributed.
Steinernema feltiae;
entemopathogenic nematode
- Target
fungus gnats, shoreflies, thrips pupae and many others
- Forage
in the top inch or two of the soil
- Water
into your growing media lightly- if they get too far in, they will not work
- Not
highly mobile
- Well suited for greenhouse environments with an
ideal temperature range of 10-25oC (50-78oF)
- Susceptible
to being washed away in rockwool
- When
growing in rockwool, apply after the last irrigation of the day to give
them a chance to establish
By
ensuring thorough protection against all life stages of the fungus gnat, you
should be able to keep populations at bay! Prevention is everything, so be sure
to apply biologicals preventatively and as needed.
Posted by: Talia Plaskett