LEDWisdom Plant Pests Article Series #2 Fungus Gnats
LEDWisdom continues its series on plant pests with a focus on fungus gnats. Fungus gnats are dark-colored, short-lived gnats that resemble small fruit flies. If your plants are infested, you can see the gnats crawling on the soil surface if you look closely. Unlike some other pests, fungus gnats live in the soil and don't pay much attention to your plants' leaves or flowers. Instead, the larvae that hatch from the eggs they lay underground feed on and damage your plant's roots to reach adulthood. Since the root system is critical for healthy growth, a fungus gnat infestation can have devastating consequences. In this article, LEDWisdom will share several solutions to help you get rid of fungus gnats.
Fungus gnats are almost always an indicator of humid conditions in your grow room and often appear when plants are overwatered. Because they are difficult to spot once they appear, the problem can become persistent.
Fungus gnats go through four stages during their development: egg, larva, pupa, and adult. Under suitable warm and humid conditions, adult females lay hundreds of eggs in the soil. The larvae feed for about two weeks and then pupate near the soil surface. After 3-7 days in the pupal stage, adult gnats emerge and live for about eight days. It takes about 3-4 weeks for adult gnats to develop from eggs. So even if you get rid of the problem, you need to make sure you don't see any gnats for the next 3-4 weeks.
Since fungal spores are almost always around us, all the conditions mosquitoes need to reproduce are water and organic matter. If plant growing media purchased from building and garden stores are not properly sterilized or stored, they may contain fungal mosquito eggs.
Fungus gnats don't primarily feed on the roots of your plants. They prefer to feed on fungal growths and decaying matter in the soil. However, when the organic matter in the soil is depleted, they begin to pose a problem for your plants. In this case, fungus gnat larvae feed on and damage the root hairs and delicate plant roots.
The fertilizers we use to feed our plants may be organic, and because we apply these fertilizers continuously, the larvae of the fungus gnat may not harm the roots of your plants. However, if the problem is not addressed, the number of mosquitoes and consequently their larvae will increase significantly, causing permanent and extensive damage to your plants.
When roots are damaged during a fungal mosquito infestation, plants may show various disease symptoms such as yellow leaves, wilting, spotting, and drooping. Even with the correct pH and appropriate nutrients, signs of nutrient deficiencies (diseased growth, leaf discoloration, etc.) may appear. Seedlings weaken, fall over, die, or become stunted. Slowed growth and reduced yields are observed.
Diagnosing a fungus fly infestation is relatively easy. Fungus flies are very small, but you can see them if you get close enough to your plants. We can list a few methods for diagnosing this infestation;
• Observe for tiny flies crawling or jumping in the soil around your plants.
• Using a magnifying glass to inspect white worms wriggling in the soil, as they are very small and may be hidden, making them difficult to spot.
• Pale leaves, spots, brown edges on leaves, drooping, and many other unexplained symptoms can point to mosquitoes, and since these symptoms can manifest in the same way as other plant problems and diseases, incorrect intervention can occur. Therefore, taking all necessary precautions before an infestation occurs is the most effective way to protect against it.
Approaching the issue from another angle, fungus gnats can provide you with useful information as they will alert you to problems with your watering routine. When they appear, it is often due to overwatering your plants. Let's move on to our list of solutions that apply to all growing media.
• Less frequent watering
The first and most important thing you need to do is readjust your watering routine. If your growing medium is soil, allow the soil to dry out completely between waterings. Often, doing this will resolve the fungal mosquito problem on its own. If you're unsure how often to water, you can check if the pot feels much lighter than it did the last time you watered it by lifting it.
• Yellow sticky traps
Purchase yellow sticky traps from a garden store and place them around your plants. These traps attract fungus gnats that will stick to them. It's important to remember that yellow traps alone won't completely eliminate an infestation. However, they are a good indicator of whether fungus gnats are (still) present in your plant growing cabinet or area, and are effective tools for hunting adult gnats.
• Neem oil
If you have a pest infestation, you don't need to overdo it with chemical pesticides. Neem oil can help control your infestation. It's also a good preventative measure. You can apply it to the top layer of your soil to kill larvae. It's not considered a definitive solution, but as a natural remedy, it can be a viable preventative measure.
• Blow air onto the soil surface.
A simple fan that gently blows air into your soil has many advantages. One of them is making it harder for insects to land on the ground. It will also help the soil surface dry out faster, eliminating mosquitoes.
• Apply mulch to the soil.
Since fungus gnats live and breed in the soil, you can cover your growing medium with sand, gravel, or perlite to make it difficult for them to enter and exit the soil. However, covering the soil may not be practical as it eliminates the possibility of visually checking the dryness of the medium. Using mulch plastic can also prevent air from entering your growing medium, leading to mold growth. Therefore, mulch should be applied using breathable materials.
• BT bacteria
Among expert growers, the bacteria Bacillus thuringiensis is a common solution for getting rid of caterpillars. There is also a variant of these bacteria that works on fungus gnats and is known as Bacillus thuringiensis israelensis. Simply adding water is enough to apply it.
• Sterilize your soil
In some cases, for example, if insect larvae or eggs are already present in the soil, you cannot prevent the appearance of insects. To be on the safe side, you can sterilize your soil. After placing some soil in a flat container, such as a baking sheet, cover it with foil. Bake in the oven at 82–93°C for at least 30 minutes. While waiting for the soil to be ready, you can take care of cleaning your pots and growing area. In this way, you can minimize the risk of any kind of disease, fungus, and pest infestation.
Among the methods listed above, the only one that provides definitive results is the use of BT bacteria, but using bacterial beds or bacteria in powder form is not always economical and accessible. Therefore, we are sharing with you our method, applicable to all plant growing media, which combines the other methods mentioned above (excluding bacterial use) to definitively prevent mosquito problems;
Instead of trying to grow larger plants by using bigger pots, work with more pruned plants in smaller pots to prevent them from crowding together.
- Opt for fabric pots. Cover the surface of your pot with only a 1-2 centimeter layer of perlite until your plant grows, and continue watering from the surface until the seedling becomes a plant. If mosquito problems increase, spray a neem oil mixture onto the perlite layer after watering, or use the tray watering method we will discuss in later points.
- Use yellow traps. As the number of flies you catch in the yellow traps increases, increase the number of traps. These methods will help keep the mosquito problem under control as your plant grows.
- Water from the tray. Since fungus gnats live and reproduce in the soil, their breeding cycle will only be disrupted and they will disappear from your growing area if their entry and exit from the soil are prevented. Mulching with perlite or gravel can be a solution for small infestations, but it may not provide a definitive solution for every infestation. Continuously spraying the perimeter of your growing area and constantly disinfecting the inside of your growing area will greatly reduce the likelihood of problems. When you water from the tray, the surface of the material you use in your mulching application will remain constantly dry, increasing the efficiency of the application.
- Use diatomaceous earth. Watering from the tray will leave your mulch layer dry. By sprinkling 0.2-0.5 cm thick diatomaceous earth on top of your 2 cm perlite layer, when adult mosquitoes land to lay eggs, the micron-sized diatomaceous earth will stick to them, dehydrating and destroying them. Similarly, pupae and larvae trying to emerge from the soil or crawling on the surface will also be destroyed. If the diatomaceous earth and perlite layer is kept constantly dry, you will likely not have a mosquito problem. The top layer should be constantly renewed when transferring from small pots to larger pots. Bottom watering is the only other alternative solution that can be used by those experiencing mosquito problems when they do not have access to bacterial products.
Mosquitoes are very persistent, and as we mentioned, there are few ways to get rid of them. At LEDWisdom, we've shared the methods we use in our test greenhouses to help you overcome mosquito problems. In our next article, you can find similar diagnostic and solution suggestions for spider mites. You can subscribe to our site to be notified when our articles are published.