With houseplants, most pest problems stem from a separate issue: water, light, relative environment, and/or nutrients. Healthy plants are much more capable of resisting pests than plants under environmental stresses. So a good start to combat pests is to provide favorable conditions to start with, but there are also some methods to handle outbreaks after they happen.
By taking preventative measures and considering environmental conditions, problems can be avoided before they manifest. While you can consult our other posts for information on proper light, water, base nutrients, and preventative additives, there are a couple other environmental factors to consider. Relative humidity and temperature can play a large role in plant health. It is common for relative humidity to be low for plants sited under lights, in bright sunny windows, by vents, or in any space where the heat is running frequently. In these conditions, mealybugs, spider mites, and scale will thrive.
Some plants, especially tropical houseplants, struggle in cold, winter-like temperatures that can result from being left on an outside porch, sitting next a drafty window, or near a frequently opened door. The extreme stress of cold burn can open the door to an onslaught of pests. On the other hand, temperatures that are too high cause frequent wilting, which is another extreme stress. In general, maintaining stable temperatures and rates of humidity helps create healthy plants, which are more likely to ward off most pests.
Unfortunately, however, even healthy plants can fall prey to pests and will require some pest control management. When that happens, the best recommendation is a solution that matches the level of the problem. If you catch the problem early, a good first step is a solution of water, 10% rubbing alcohol, and soap, either a mild dish soap or safer soap, which should be applied weekly. This works well on small infestations of mealybugs, spider mites, and scale, the most common houseplant pests. With this approach, it also helps to wipe down the leaves of the plant. Use a rag wetted with the same solution.
If this initial step doesn’t work, or if the infestation is more significant, your best bet is to move up to a pyrethrin product. This product will kill the insects on contact, but will likely take several applications for complete eradication. If there is a very large infestation, like snowy looking leaves from a severe mealybug infestation, or an infestation that isn’t being affected by the other solutions, mix both pyrethrin and Azamax in a solution to spray the plant and drench the roots. Remember, if your houseplant does get pests, look to see if there are any stress factors that you can change.