Plant Pest Series: Part I

7 Steps For Stopping Fungus Gnats in Their Tracks

What Are They? Fungus Gants are tiny flying insects that swarm around affected plants. You may see them on nearby windows, flying above your plants, on the leaves, or even on the table top. Even if you don’t see them there, check the surface of your soil: you will notice little mini insects walking over your soil. They may seem harmless, but think again! Adults can lay 300 eggs at one time, that hatch a week later. They can damage seedlings, stems and plant roots by feeding on them… Gnats are bad news! Read on to learn how to stop them in their tracks!

Preventative Measures
Step 1: Check new houseplants before you buy them! Inspect leaves [particularly the undersides], stems and especially the roots thoroughly for problems. Removing the root ball from the container is okay to do, and is certainly a good idea! Using a finger, disturb the soil a little to see if any gnats fly out. If so, this particular plant is already affected.

If you notice any yellowed leaves, black spots, sunburned leaves, curling, mushy roots (usually dark brown or even blackened in color) or weak stems that easily flop from side to side when shaken, the plant is definitely not for you! It clearly shows signs of neglect, and most likely disease. Be sure and choose a healthier looking plant!

Step 2: Just in case, isolate newly purchased plants for a couple days to see if any problems manifest. Keep them away from all your other plants, so as not to spread any pests to other plants. After a trail period, if no pests show up, put the plant with your others with confidence!

Plants thrive in conditions anywhere between 65 – 75 degrees. Cooler than 65 degrees can result in cold injury, whereas warmer than 75 degrees can parch your plants very quickly and slow their growth. In terms of temperature, the best conditions for plants is in a room kept somewhere between 65 – 75 degrees.

Dealing With Gnats
Step 1: In cases of fungus gnat infestation, soil will be very moist and generally in a warm environment (70 degrees or more). Try lowering room temperature if possible. Or, try move the plant next to a window in the fall and wintertime, where the temperature will be slightly lower.

Step 2: Make sure your plant has good drainage. If not, you may need to repot it (see Step 8)

Step 3: Water a bit less frequently, giving the plant time to dry out just a bit between watering. It should be slightly moist to the touch, but not sopping wet. Let the plants’ soil dry slightly (but not entirely). Drier soul will help kill the larvae (baby fungus gnats) that hatch from microscopic eggs laid by adult gnats within your plant pot. In a moist environment the eggs will hatch, but if the soil is on the dry side, the eggs simply dissolve before they hatch.

Step 4: Wine or apple cider vinegar attracts fungus gnats because of its pungent smell. Place a small bowl of either wine or vinegar near the affected plant(s). This will draw out the adult gnats, which will come to investigate. Upon landing in the bowl, they will quickly drown.

Step 5: Top your plant soil with sand. This makes the soil much less attractive to the fungus gnats, since they prefer moist soil. If they fly to your plant and feel the soil is dry, they won’t bother it. Keep in mind that moist soil underneath the sand will still harbor gnats, so be sure to let the plant dry a little bit.

Step 6: Place homemade gnat traps in your affected plants. They are very easy to make.

You will need:
Popsicle sticks OR a dowel rod OR a chopstick (your choice);
3x5 cards OR heavy-duty paper OR thin cardboard;
Elmer’s glue;
Scotch tape OR masking tape OR double-sided tape (any kind of tape will work, but double-sided tape is especially good for these)
If you'd rather use fly paper traps, you can secure them to the stick the same way as the guy in the photo, below:

1. If using a 3x5 card, leave the size as is. Otherwise, cut the cardboard into 2” by 2” squares for much smaller plants or 4” by 4” for larger plants, etc. (The idea is to make the trap the right size for your plant so it’s not bumping into leaves or stems.)

2. Using the popsicle stick as a base for the trap, glue the 3x5 card to the popsicle stick – you can use two pieces to make the trap double-sided if you wish.

3. Then, using double-sided tape, cover each side of the card completely. Make sure the sticky side faces out [in case you didn’t have any double-sided tape]. Or, use fly paper and secure it to the popsicle stick.

4. Place the traps in your affected soil, sticking them deep enough so they don’t topple over. As the gnats fly about, they will get stuck to the tape and die. Discard traps later. If your infestation is severe, use several traps coupled with any of the other methods described above!

**Making your own traps from scratch will be much cheaper than buying either fly paper or whitefly traps. Whiteflys are another type of houseplant pest -- I will post on them soon! ** If NONE of the above ideas are working, read on:

Step 7: Repot your plant completely in fresh potting soil. To increase drainage, place potsherds or stones in the bottom of the pot before you place in the plant. For additional drainage, mix your standard potting soil with sand [sharp sand is best, or you can use sandbox sand]. Water your plant, and then top the soil with a layer of sand to further deter the gnats from ever coming back again! Good luck!

Keep an eye out for the next part in my Plant Pest Series, Part II: Spider Mites!