Plant Pests: Spider Mites & Whiteflies & How To Control Them
Even though you might keep your garden or houseplants well tended, pests can seemingly appear out of nowhere. What’s up with that? This is why it’s important to know what’s attacking your plants with proper i.d. and then spring into action. Last week I covered aphids and mealybugs. This is all about spider mites and whiteflies and how to control them.
Both spider mites and whiteflies are soft-bodied, sucking insects. They slowly suck the sap out of a plant which over time weakens it, stunts the growth and deforms the flower. You can liken sap in plants to blood in animals. The sap contains sugar which these pests love, as do ants who in turn flock to an infested plant.
Here’s a red spider mite close up. You’d need a magnifying glass to see it.
Spider mites are hard to identify until the damage is already done, because they’re so tiny. They’re difficult to see without a magnifying glass but can be red, greenish or light brown. If you think your plant is infested with them, just put a piece of light colored paper under the leaf and tap, tap, tap. When little specks fall onto the paper, then you can i.d. them.
Spider mites are actually related to spiders. They generally hang out on the undersides of the leaves. If you see the leaves yellowing, mottling, specking and eventually turning brown, then the infestation is getting bad. The leaves will fall off and webbing (usually at the top where the new growth is) will appear when things are getting really bad. When it reaches this stage, it’s hard to bring the plant back to health.
Spider mites breed like crazy. When I was starting out my horticultural career in Boston as an interior plant care technician, they would explode on the scene in late fall/winter when the heat was turned on. We had to replace a lot of Dracaena marginatas, Bamboo Palms, Areca Palms and Neanthe Bella Palms on commercial accounts due to bad infestations. So, if you have houseplants, be sure to check them for spider mites at that time of year. If you prefer to grow your own, keep your eyes open for spider mites (as well as thrips) infesting pot.
Whiteflies on the other hand, are very easy to spot and i.d. They’re small (but big enough to see), white and fly off when you touch a plant. It’s actually the adults that fly and that’s what makes them hard to control. At juvenile stage they just hang out on the under sides of the leaves.
Whiteflies, like aphids and mealy bugs, secrete sugar that they can’t ingest when sucking the sap. This causes the leaves to get sticky. You might see a black mold forming and that’s actually a fungus which grows on the sugar. That’s what happened to my client’s large garden in the SF Bay Area – a lot of the plants (all of which bloomed) had a coating of black soot on them. I had just taken the account over and called in an environmental pest control company to do a series of sprayings with insecticidal soap because it was more than I could handle. It did the trick but took almost a year to get it under control.
Whiteflies on the underside of a leaf. You can see a bit of the cottony threading here.
When the infestation worsens, you’ll see white cottony threading appear on the undersides and edges of the leaves. There was a row of hibiscus trees along the sidewalk in Santa Barbara which looked like they were coated with snow in August. They were stressed from lack of water and would always get a bad infestation of whiteflies. The leaves looked like they were edged with white cotton candy!
Besides on hibiscus, whiteflies are commonly seen in greenhouses and on tomatoes and flowering plants.
How To Control Spider Mites & Whiteflies:
Release ladybugs or lacewings in your garden as a method of control. Lacewings devour soft bodied insects much faster than do ladybugs. This obviously isn’t a viable solution for your houseplants! There is a predatory mite which control spider mites & a whitefly predator for the whiteflies. Both eat the eggs which is a good way to prevent future infestations.
2)Spray with water using the garden hose, kitchen or bath spray.
This is the method I fall back on. You want to gently blast off (no fire hose action here please) the pests & their eggs. The spray in your kitchen or bathroom will be suitable for your houseplants if you don’t have access to a hose outdoors. For these 2 pests, this method is a partial control. You’ll get the many of the adult spider mites & their eggs, but it’ll only work for getting the juvenile whiteflies & the eggs.
3) Insect killer sprays.
I don’t use chemicals so these are considered to be “natural controls”. They include: horticultural oil, insecticidal soap & need oil. Most plants can be sprayed with these but just check 1st. You can do a little research & see which would best for you.
Here are some options: insecticidal soap ready to use, insecticidal soap concentrate, horticultural oil ready to use, horticultural oil concentrate, neem oil ready to spray & neem oil concentrate. This 1 lists itself as a houseplant & garden insect killer.
4) Homemade spray recipes.
Here’s the way I’ve always made an soap/oil spray: Mix 1 tablespoon mild dish soap or Dr. Bronner’s, 1 tablespoon vegetable oil & 1 cup water. This works for a mild infestations of whiteflies although the adults will fly away.
Here’s what I’ve used to control a mild infestation of spider mites: Mix 1/4 cup apple cider vinegar (white vinegar is fine too) with 1 cup of water, 1 t of baking soda & a few drops of mild dish soap into a spray bottle.
Rodale’s, a source for living naturally which I’ve known about & respected for a long time, has a recipe for this natural pest spray with garlic, onion & cayenne pepper.
5) Sticky Traps
I used sticky yellow traps to get the adult whiteflies. Hang them in or right next to the infested plants. The whiteflies are attracted to yellow & fly right into the sticky traps.
Webbing on the new growth caused by an infestation of spider mites.
Things to know about spider mites, whiteflies & their control:
* Both whiteflies & spider mites can be found on the undersides of the leaves.
* Both have soft bodies so they’re easy to control if you catch them in the early stages .
*Which leads me to: control these pests as soon as you see them. Once the infestation gets bad, they’re hard to get rid of. Your plant may not recover. This is especially true of a spider mite infestation.
*Ants are after the sugar residue left behind by the whiteflies. Once the insects are gone, the ants will be too.
*The leaves of the plant can get sticky – that’s caused by the sugar secretion. You might see a black residue (the fungus) appear – you’ll want to get rid of that too.
*If you choose to spray as your method of control, you’ll need to repeat. Follow the instructions on the bottle as to how often. A homemade spray you can repeat every 7 days. It might take 3-4 rounds to control the pests. Make sure the plant isn’t stressed (ie bone dry) before spraying. And, don’t spray in the hot sun.
*It’s very, very, very important to spray the undersides of the leaves thoroughly. That’s where these pests hang out.
*Be sure to inspect any new plants you bring home to make sure they’re not carrying any pests.
*The same goes for plants which have summered outdoors. Check them for pests before bringing them in for the colder months.
Hopefully, your plants never get spider mites or whiteflies, but if they do, now you can identify them and take action.
Happy (pest free) gardening & thanks for stopping by,