Scale, Gnats, Fungus, and Thrips: A Pest Treatment Guide

Mealybugs

After I posted about how to deal with Thrips last Monday, I was asked by several people for treatments for scale, gnats, and fungus. I have some experience with some other pests. It's inevitable when dealing with a plant collection of any size. Overall, I think there are really three basic parts of successful pest management -

• Prevention
• Carnivorous plants are addictive. You'll start out with one and end up with 500. So, when I talk about "prevention" what I really mean is not only choosing your sources wisely (don't buy from nurseries with known pest problems, e.g.) but also making sure you isolate new acquisitions for a month or two to make sure that you prevent your larger collection from becoming infected.
• Monitoring
• You have to look at plants and note anything unusual. Keep a log (even if its just mental) of anything "weird." That could be the sign of a pest. Document and compare those "weird" traits with online resources. That will help you identify pests. 
• Treatment
• Never let a pest linger. Treatment should be immediate. The longer you wait, the worse the infection. The worse the infection, the more likely other plants will get infected and the more likely the originally infected plant will die. 

Mealybugs on a Sarracenia

From personal experience, here's what I've found works for various different pests:

Scale

• Scale - General Rules
• A small infestation can be successfully treated by dabbing the scale with a Q-Tip dipped in rubbing alcohol. Note, however, that a small infestation is usually a sign of a larger infestation.
• I have found Orthene to be extremely effective on large infestations, but do take note that some plants, such as Nepenthes hamata and its hybrids, are particularly sensitive to pesticides so should be treated with care.
• Hawaiian Snow Scale - The Most Common Scale Pest
• Hawaiian Snow Scale is near omnipresent on Nepenthes grown outside in Hawaii, but normally does not manifest until adverse conditions are encountered and the plant is stressed. This means that if you receive a Nepenthes from Hawaii and your conditions are less ideal than Hawaii's (trust me, unless you're also on Hawaii, your conditions are less ideal), your Nepenthes will probably start to show a Hawaiian Snow Scale infestation soon after. 
• Hawaiian Snow Scale is particularly difficult to eradicate and will take a number of treatments over several months. Quite honestly, the plant is often not worth the effort in eradicating them.

Fungus

• Fungus - Soil Based
• At times, you will notice a grey fungus covering the soil. This grows when the soil is very moist and not enough light is reaching it. This fungus can easily kill seedlings and can have some effect on larger plants. 
• The easiest way to treat the fungus is to remove infected portions of the media and/or spray with diluted hydrogen peroxide. Typically, I buy the strength sold to treat wounds and dilute to quarter to 1/10th strength.

Fungus Gnats on a Pinguicula Leaf

• Fungus Gnats
• Fungus gnats are a perennial problem. They're the little flying insects that you sometimes see around your plants, particularly if your plants have damp media. In small numbers, the adults are good food for your sticky-leafed plants (Drosera, Byblis, Pinguicula, etc.). Unfortunately, adults mean larva, and larva eat plants.
• The easiest treatment is to allow the media to dry out a bit more. If your conditions are so wet that you have fungus gnats, you probably need the plants to dry out a bit between watering. The second easiest treatment is to cover the media with a thin layer of coarse sand. This is particularly helpful for pots of Drosera and other, smaller plants, which are easily damaged by fungus gnats.

If you want to read more about pest management, I do have a chapter on that subject - and many others - in Cultivating Carnivorous Plants.