Common Houseplant Pests Part 2 - Fungus Gnats, Springtails

Winter is the time of year where I have more opportunity to examine things. And upon further examination since my previous part 1 post, I have more invaders in my house plants...quite hidden from view. Yep, I have more unwelcome roomates -oh, no! :)

There are a group of tiny insects that make their home in house plant soil. Fungus Gnats, Springtails and Psocids are really hard to see. In fact, when I was young, my mother used to call me to the living room and have me watch her water the house plants to see if I saw little squirmy larvae or tiny insects float and scatter when the water puddled on the soil surface. Mom was far sighted and I was near sighted. I loved to do this for her, as my inquisitiveness of plants and what "bugs" them happened already at that time.

This Chrsitmas Cactus ( Schlumbergera bridgesii ) has got to be at least 20 years old. The main stock at the base is thicker than my thumb. I've pruned it back so often. So happy it lives on! It was a gift to my mother and I have inherited it. Since it is that old, and since I re-pot it so infrequently, the soil is older and many leaves and plant debris have accumulated in the pot over time.  I find, the more I neglect this plant, the more it thrives.

I watered this Christmas Cactus more frequently this past month, as it went into bloom. I wanted to make sure the blooms lasted longer with added moisture. Now I am paying the price for the increased saturation levels. Worth it to me, as I had a tremendous show of bloom.

Unfortunately, I had no success photographing the insects, as you can see here, my camera cannot magnify enough to capture them.  However, like the time my mother asked me watch while she watered, I've videoed the same way and uploaded it onto Youtube for you.  

The best way I could suggest to view the video is use the expanded view (bottom right corner on the video link) and to fixate your eyes towards the lower centre of the video. I believe I have both Fungus Gnats and Psocids in the soil. You'll see them floating on top of the water, but I have placed a focus box where I saw larger Psocids moving over a pebble once the water dissipates. Fungus Gnat larvae are more worm like and Psocids are more crawlers. Both are sooo tiny, so you'll only notice movement, as apposed to a vivid colour or shape. Hopefully you can see them.

Even blown air over them makes them move, that way you're not over-watering in order to see them disperse.

Fungus Gnats, Springtails and Psocids LOVE MOIST conditions. As one of their name suggests, they love to feed on fungus that soil incubates when it remains consistently moist. They also feed on plant root hairs that can cause reduced plant health, so sometimes a watchful eye can see a plant lose some of its vigor and notice insect damage before being able to visually see the bugs. They are not the most troublesome of pests to have, although, enough populations of them (like my situation), you want to take some action.

The adult stage of the Fungus Gnat is a winged stage.I knew I had them in this pot with the Psocids because as soon as I took hold of the plant, small flies flew away.  Like white fly, with just the slightest disturbance, you'll see them fly and scatter about. Unlike Whitefly, they are dark and slightly larger. They also return to the soil level, where it's moist to lay eggs. When I see larvae moving about at the soil level, I usually tap some of the leaves in order to check for any adults flying about as well.

Springtails and Psocids are different, as their adult life cycles stay tiny and they remain at the soil level. Springtails jump when disturbed, whereas Psocids just move about. I find these guys sometimes at the base of the pots, often soon after watering. They float more easily when you see water puddling at the top. They don't bother me as much, as they eat primarily decaying matter and help compost leafy bits and bark. Yet, sometimes they are useful in detecting other soil borne insects, as other insects like mites can feed off of them. When you have a host of soil loving insects, you usually have other pesky insects.

One way to prevent these bugs from invading is allowing your plants to thoroughly dry out between watering. Don't allow your house plants to sit in water. My Christmas Cactus sits in a larger decorative pot. More water puddles below, and it allows for a breeding ground as you can see. Let the soil go completely dry to the touch, making it inhospitable for new generations to breed.  This is tricky, but can be achieved. You don't want to let the plant completely dry out in some cases (ferns for an example) as many love moist conditions. However, one way is to water the plants from the base of the pot. Filling a saucer or bowl with a few centimetres of water and then sitting the planter pot into the saucer and allowing the holes from beneath the pot to suck up the water. Once all the water is drawn up, remove the saucer and place the house plant back to begin drying out again.

Many plants you buy (even from reputable garden centres) have these bugs. They are just so tiny and hide under soil bits, one can hardly tell if you are bringing them home. When you do bring plants home for the first time, place the pots in a sunny window, allowing the soil to dry out more rapidly. Hold off watering them for a bit, or water from the base as suggested above, especially when the plant needs it. This prevents prolonged moist conditions, making it unfavourable for the insects to feed and breed.

Most tropical, indoor plants enjoy drying out periods between watering anyway. This is a good practice to keep soil borne bugs at bay. For some house plants, the dry conditions encourage flower bloom, giving the plant just a limited amount of stress to trigger the plant to produce flowers.

For much more troublesome insect infestations, a soil drench is a definite solution. The picture on the right is a product I bought over 10 years ago. A simple houseplant insect soil dust. You sprinkle this powder over the soil and then scratch it in and water through. It remains in a powdered state for a day or so and as the water leaches down, it comes in contact with larvae, adult bugs and their pesky eggs.

In Ontario, this product is no longer available, as it is chemically based, and new pesticide laws don't allow it to be sold at the retail level, but it is still available commercially with a pesticide license, just in different packaging.

One other soil drench that I have heard is effective: tea-tree oil, but I would be careful to only use very diluted mixtures, as direct tea-tree oil on roots can burn and damage tender root hairs. Also I have read the use of Neem Oil is effective as well. Be sure to read the bottle for directions before applying.

I've also read using thick potato peels and laying a few on top of the soil, skin side up. Leave for a day and remove them quickly from the soils surface, as the insects have begun to eat and bore through the peels. You'll notice several will stay stuck to the peels when you discard them.

One other hint:  if you notice one of your houseplants has these insects, and the insects have not moved to other plants, remove the plant from its location and proximity to other neighbouring plants. Soon enough, when populations increase (especially with Fungus Gnats) and adults fly about, the gnats will travel to other suitable conditions where they can lay more eggs. Place the infested plant a good distance away and leave there until you don't notice the Fungus Gnats anymore.

Time for this Christmas Cactus to move to a brighter area and no more watering for a while!