Houseplant pests series part 2: Spider Mites

This is my second in a series of posts I am doing about common houseplant pests that can plague the indoor gardener. In my last post I wrote about soil gnats, today I will talk about spider mites. 

Spider mites are sneaky little suckers. They are difficult to see, and usually by the time you notice them, the plant is already heavily damaged. You might notice spider webbing on the plant or the plant may simply look dirty. From a distance, you might think that the plant isn’t getting enough water…but take a closer look, hold the plant up to the light and look under the leaves and see what you find. Usually you can see the tiny little mites moving around on fine webbing. Yuck!

Spider mites

Spider mites multiply very quickly and, in the right conditions, can as much as double their population every couple of weeks. Spider mites become fully grown about a week after they hatch. It only takes a few weeks for an adult female to lay hundreds of eggs, and for those eggs to start to hatch, resulting in exponential population growth.

In my experience, spider mites are one of the most destructive pests. They can devastate or even kill a plant in a very short period of time. Spider mites suck the sap out of the leaf leaving it looking discolored, speckled, curled under and, at its worse, dried and shriveled up. The infested leaves will die and start to fall off, which will ultimately kill the plant.

Spider Mites make new growth shrivel

Spider mites thrive in warm, dry conditions. During the winter, your house becomes the perfect breeding ground. They will start to breed and feed on older leaves, and are not common on new growth. They tend to start their webs on the underside of leaves and at the leaf joints.

Spider mites are not technically insects, therefore cannot be controlled with insecticides, systemic or other. There are pesticides that are specifically designed for mites, but spider mites may develop resistance to them in a short time. I’ve found that the best way to control a spider mite infestation, and eventually eliminate them from a plant, is by washing the leaves with plain old soap and water on a regular basis. You have to be diligent and continue to do this even if you don't see any bugs. During the winter, I try to be proactive with the plants that seem to be most susceptible to spider mites by cleaning the leaves at least once a month, even before I see any signs of the pests. If you see there is already an infestation, clean the leaves on the infested plant once a week or more until you have it under control. It’s a good idea to clean the leaves of any plants that are close to the infested plant as well.

Here are some other thing you could do to control spider mite infestations on your houseplants:

• Since spider mites thrive in dry conditions, keeping the air around your plants humid may help prevent infestation. Unless you have a greenhouse this is difficult with houseplants, especially in the winter. One way to achieve this is by spraying the plant with water from a spray bottle regularly. In order for this method to be effective, you must spray your plants once or more a day. You could also try leaving a container of water near the plant or using a humidifier to help keep the humidity up around your plants.
  
• Spray the leaves on an infested plant with a strong stream of water to dislodge mites and webbing. (Be careful not to damage the plant) This will help to slow down the production of new eggs, and kill mites and eggs.
• Make sure the plant is healthy and maintain adequate soil moisture. Maintaining healthy houseplants will allow them to protect themselves against spider mite infestations.
• Trim heavily infested leaves from the plant and throw them in the garbage (but don't remove all the leaves).
• Rinse or wash plant leaves on a regular basis. Small plants can be brought into the shower or sink to make this task easier. You can use a rag and spray bottle to wash the leaves of large plants. Continue to do this treatment weekly until the problem goes away. You may want to continue this routine on a monthly basis on plants that have recurring spider mite problems. Prevention is key.

The best way to avoid heavy damage to your plants caused by spider mites is to start treating the plant as soon as you discover the pests. As with any houseplant problem, make sure you check your plants on a regular basis (each time you water) for any signs of problems. For general pest control and prevention tips, read my Pesty Pests blog post.

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