Spider Mites and How to Deal With Them
Spider mites. They are a terrible pest that are dreaded by plant enthusiasts everywhere. They're small and hard to spot, they damage plants, and worst of all- they are hard to get rid of! There will be photos throughout this post that depict spider mites and their damage. I want to emphasize that the plant these photos depict had an extensive infestation. You do not have to wait until your plant gets this bad to diagnose spider mites- it's better if you don't! I just find it much easier to see and understand what to look for with these photos.
Spider mites are a small spider relative that have piercing-sucking mouthparts. There are 1,200 or more species of spider mites, but don't let that intimidate you! They have similar ID and effective treatment. They do spin webs, but the damage they cause to the plants does not come from this webbing. They feed on the sap produced by the plants. This style of feeding can transmit plant diseases like viruses, many of which do not have a cure. So, in order to protect your plants from this pest that potentially can lead to other diseases, it is important to scout, properly ID, and effectively treat as soon as you see them. Like with all pest control, the first step is to know the proper identification of what you are looking at during a routine scouting.
What to look for
Spider mites aren't like other pests that are easily spotted sitting against the foliage. They're incredibly tiny, less than one millimeter long, but can vary in size and color. For spider mites, it may be easier to look for other signs and symptoms before looking for the pest themselves. On the right, there is an extreme example of the yellow stippling that is caused by the process in which spider mites feed. They use their specialized mouthparts to stab a hole in the leaf and suck the sap from the leaf. This is not unique to spider mites, as this stippling pattern is caused by other plant pests with the same piercing-sucking mouthparts. Because of this, you cannot solely rely on the damage they cause as a definite identification method. If you suspect spider mites are the source of the stippling on the plant, look a little closer. Spider mites are tiny. You may need a hand lens to see them well. Without one, they tend to look like specks of dirt, usually on the underside of leaves. You may see them moving about. If the suspect specks are stationary, I don't suggest touching them to encourage them to move, because they can easily hitch a ride and end up on another plant in your collection. Always wash your hands thoroughly between plants with suspected pests and healthy plants! A telltale sign of spider mites, aside from seeing the actual pests themselves, is their webbing.
It is important to remember that spiders and spider mites both create webs that are used in differing ways. The spiders that many of us see and may be frightened of in day-to-day life use their webbing as a tool to capture prey. Typical spider webbing tends to have visible spaces between the individual strands, like your typical cobwebs and spider webs you've seen around. If there is only one, easily visible spider in the web, this is not a spider mite web. Spider mite webs are used as a network for travel and as a place to live. Because spider mites are so much smaller than a typical spider, the webs are made of a finer material and have significantly smaller spaces between. They look like fine cobwebs- but it's important to note that cobwebs are not made by spider mites. Below, there are two photos. One of spider mite webbing, one of the average cobweb. Can you tell the difference? Take a guess which is the spider mite webbing before you continue reading.
The webbing on the left is an average cobweb- this was made by a typical spider. The webbing on the right is much finer; the space between the strands and even the individual strands themselves are difficult to make out. The small specks inside the webbing are the spider mites themselves. There is something else that is important to understand before looking at treatment options...
Understanding the life cycle will help to understand how to treat the pest you are dealing with. This will help you to treat them the most effectively before the pests have the chance to cause extensive damage. Spider mites tend to thrive in hot, dry climates. In warmer regions, as well as indoors, they will continue to lay eggs all year long. Under optimal conditions, some species of spider mites can hatch in as little as 3 days and reach maturity in 5. When they hatch from their egg, the spider mite only has six legs, but come time to molt after feeding on their host plant for a few days, they gain the extra pair of legs, showing their resemblance to a spider. Two more molts occur before the spider mite is sexually mature and ready to begin making new spider mites. An adult female can lay up to 20 eggs per day and live for 2-4 weeks. This fast reproduction period gives the spider mites the ability to adapt and develop a resistance to certain pesticides extremely quickly. The best way around that, if you decide to go the pesticide route, is to switch up the pesticides you are using frequently. Not just the brand, as they could still have the same active ingredient and functions, but the delivery method, as well. Otherwise, the way in which the pesticide kills the pest. Catching them early is key to quick and effective treatment.
Monitoring or scouting your plants regularly is the best way to stay on top of pests and keep them in check in addition to preventative measures. Increasing humidity and moisture is an effective way to help deter the spider mites. Spider mites, like other pests, often are found on the underside of leaves if not in their webs. They're also more likely to attack the tender new growth of a plant. It's a good idea to give your plants a good look through once a week, especially if they live outside or you bring home new plants. Keeping new plants isolated is a good idea if you have an extensive collection where pests could quickly travel from plant to plant. Due to the amount of species of spider mites, there are many plants that they will attack if given the chance. Keep a special eye on those plants that are existing at room humidity, those with broad leaves, and any new plants you have just purchased. Plants that are kept in higher humidity areas like greenhouse cabinets or bathrooms tend to have less instances of spider mite infestations, though this is not to say they are immune and should still be checked for pests regularly.
Treatment and Control
As stated above, pesticides are an option for effective spider mite treatment, though it is not a good idea to continuously use the same pesticide for spider mites, due to their ability to become tolerant quickly. Using pesticides in combination with one another can be effective, such as a systemic treatment and a foliar spray, but this is not always recommended. Read all pesticide labels and follow the directions for application, as those labels as written are the law.There are many types of insecticidal control, like horticultural oils, soaps, and what you traditionally think of as a pesticide. Just be sure whatever you are applying states somewhere on the label that it is rated for and will target spider mites. That being said, pesticides are not the only option.
A hard spray of water from the hose may knock a fair amount of spider mites off of the plant, leaving you with a smaller spider mite army to battle. Beneficial insects are a great alternative to insecticides and should not be used in tandem, as your pesticides are likely to kill your beneficial bugs, too! Different predators will attack different species of spider mites. Amblyseius swirskii, Neoseiulus californicus, and Amblyseius cucumeris are all mite predators that prey on several common types of spider mites. Some also feed on other common plant pests like thrips. They are also all species of mites, however these mites will not attack your plants. Instead, they eat the pests attacking your plants! Beneficial insects will continually attack the pests in your home, even while you are away. Even with beneficial insects, a second application may be needed to fully eradicate the spider mite infestation.
Be sure to check your plants, even if you have already implemented a treatment, no matter the pest. The quick reproductive time of spider mites provides a challenge when trying to decrease their numbers.
Overall, spider mites are an intimidating plant pest, but by no means do they spell doom for all of your plants. Now that you are armed with the information needed to help ID them properly, as well as several options for treatment, your plants will thank you! As always, if you have any questions about your plants, please feel free to reach out.