Question
I noticed some grey fuzz growing on the layer of moss covering my drosera
pot in my terrarium a few days ago. I've tried upping the light levels, but I
had to resort to trey watering with a fungicide. So, I added a couple of drops
(about 1/4 a tsp) of Physan 20 to an 8th a gallon of water. Then I poured
some of the mix into the plant's watering trey and diluted it further with
some distilled water for extra measure. This is my first time having to deal
with fungicide and insectivores. Physan 20 is an ammonium chloride based
fungicide, and I would imagine that it would build up in the soil over time.
right? I don't know. The only reason why I'm using Physan is because
California Carnivores accidentally shipped it to me. I also have some Captan.
What would you suggest for an indoor terrarium? The Physan makes me a bit
nervous from all of its warning labels.   The inside of my tank is about 32 C
from all of the lights I'm using. I tried bringing down the heat by using fans to
blow the hot air away, but it blows out the humidity from my tank. I'd have
them out of the tank, but I had to resort to this, because the dew on my
plants kept drying up on the window sill. Even when I moved them to a more
shaded area they continued to not grow any new dew for several weeks. Well,
new dew would grow, but it would dry up within a day even though I was
giving it sufficient water. I have new dew now, and its accepting the flies I
give it, but I have this pesky mold problem now. Its next to a window that
gets little to no daytime light. So I use the artificial lighting. I'd move the
terrarium to a better window, but its bulky and would be in the way anywhere
else.

Answer
Hi Johathan,

Thank you for providing these details!  This helps me out tremendously.  

First, avoid using Physan 20 or any other quantaray ammonium products with your sundews.  This compound has an oxidative effect, similar to bleach.  It's fine to use with plants with tougher leaves, such as Nepenthes and Sarracenia, but sundews and Pinguicula tend to shrivel and burn if any of it gets on their leaves.  We ruined a crop of Drosera roseana and Pinguicula moranensis when we sprayed the plants to control fungus.

If you choose to use it, you don't have to worry about it building up in the soil.  It dissipates very quickly and breaks down in sunlight.

In your situation, a better product to use to control fungus is a sulfur-based fungicide.  It's completely safe to use with your plants.  It works by making the environment too acidic for the fungus. You can find prepared solutions of it at your local garden center.  Use the one made by Safer?  We use it at our nursery to control isolated cases of fungus.  

After getting the fungus under control, consider growing your plant without a terrarium.  There is where Peter and I differ regarding the issue of humidity.  I'm not a big fan of terrariums because of what you're experiencing: heat build up, poor circulation, fungal infection, bulky equipment.  Growing plants in terrariums tends to create more problems than solutions.

By and large, carnivorous plants don't need the constant high humidity of a terrarium.  Only a very small number of of the 600 or so carnivorous plant species - such as N. bicalrata, Heliamphora and Drosera falconeri to name a few - require the controlled environment of a terarium when growing them in most parts of the United States.

Drosera capensis will grow perfectly well without a terrarium and will adapt to lower humidity.  It is actually light, not humidity, that stimulates sundews to produce their dew.  The dew is actually a concoction of sugar and enzymes to attract and digest insects.  To create and secrete this concoction, sundews need sunlight.  Without sufficient sunlight, sundews won't have the energy to produce their dew.  So if the sunlight levels are too low, no amount of humidity will stimulate the plant to produce dew.  However, even in the presence of very low humidity, sundews can produce copious amounts of dew if they are given ample sunlight.

(Temperature also plays an important role in dew production.  If the temperature is too high or too low, dew production will cease.  But for most homes, th temperature is always just right for Drosera capensis.)

So if you really want to control the fungus, consider growing your plant on a very sunny windowsill without the terrarium.  A south or west window with direct sunlight will do the job.  Ultraviolet light from the sun will also kill off the fungal spores.

On my south kitchen windowsill, I have a Drosera adelae that is producing copious amounts of dew.  Many of our customers are also experiencing success in growing their plants without a terrarium.  

For more information about growing tropical sundews, read our care sheet on our main website:
http://www.cobraplant.com/caresheets

Good growing!
Jacob Farin