There are benefits to gardening in an enclosed, outdoor space like no mosquitos to bother me and not having to deal with slugs, caterpillars, or beetles that eat and devastate outdoor, open air gardens. Despite these benefits, I’ve discovered that while my garden is isolated from most pests, it’s are not immune to all of them. Actually, my garden is more susceptible to pests like gnats as well as spider mites and aphids for two reasons:
- there are no natural predators like lady bugs or lizards to eat and control them, and
- pests can be transferred not only by transplanting an infected plant from one outdoor garden to another, but they can also travel through the air.
I’ve had my plants, specifically marigolds and ranunculus, devastated by spider mites and this summer I lost my snap dragons and heliotrope to aphids. When my mums and Gerbera daisy became infected with both spider mites and aphids, I decided I needed to figure out a new approach. In my posts The Life of Wheatgrass and Containers, Bulbs, & Gnats, I experimented with baking soda, water, rosemary and neem essential oils to combat mold and gnats. This experimentation encouraged me to see if this solution would work on spider mites and aphids. I discovered that mixing 1 liter of water with 10 drops of rosemary oil kills spider mites no problem, but it did little for my aphid invasion.
After doing research on spider mites and aphids, I discovered that, despite their destructiveness, they are extremely interesting and delicate little creatures. Spider mites are extremely small and usually can’t be seen until they have completely infested the host plant and infected surrounding plants. Even though spider mites are difficult to see, the signs of infestation are much more obvious such as white or yellow specs appearing on the upper part of your plant’s foliage, webbing on the underside of leaves, and brown, withering edges of leaves. While aphids are much bigger and easier to see, signs of an aphid infestation are similar. And why do these bugs create white or light colored specks on their host plants? Turns out spider mites and aphids are vampires: they suck the water from the cells of the plant. Those white, light spots are places where the leaf has been completely sucked dry. But, never fear! Like vampires, spider mites and aphids have a weakness that not only can keep them at bay, but also kill them: their bodies are soft and waxy.
The best way to kill spider mites and aphids is to use an insecticidal soap
that will corrode their soft, waxy bodies and dry them out. According to the University of Connecticut, “insecticidal soaps work only on direct contact with the pests” and work by using fatty acids to “disrupt the structure and permeability of the insects’ cell membranes” so that “the cell contents are able to leak from the damaged cells, and the insect quickly dies.” Essentially, the aphids and spider mites that come into direct contact with the soap dehydrate and die.
I also explored alternatives to insecticidal soap which include purchasing and unleashing predatory bugs like lady bugs and six spotted thrips into the garden, rinsing foliage daily with water, and using essential oils such as garlic, rosemary, cinnamon, mint and clove. In my case, using predatory bugs and rinsing my plants daily weren’t viable options, so I chose to create my own insecticidal soap instead of buying something toxic. After experimenting with different combinations of oils, water and dish soap, I found the following solution in a squirt bottle is the most effective:
- 10 drops of rosemary essential oil
- 3 squirts of dish soap
- 1 liter water
While the ingredients used are key in efficacy, it’s also important that you follow the right method to keep these pests from coming back. It is essential that you spray this soapy solution directly onto the spider mites and aphids and that you spray both the tops and bottoms of your plant’s foliage. Doing this ensures that no spider mite is spared, no aphid is survives, and that there is no resurgence. I have been treating my infected plants every other day for 5 months now and this method has worked very well. So well in fact that the spider mites are gone and the aphids don’t stand a chance.
Even after you defeat the spider mites and aphids, there is still much to be done in the way of healing your infected plants. One of the most common after effects of caused by aphid damage is the appearance of mold. Aphids in particular secrete a substance called honeydew which is sticky and sweet and is the perfect medium for growing mold. My gerber daisy and blanket flower were hit pretty hard by mold once the aphids were exterminated. In particular, I suspect that sooty mold is what coated their leaves.
According to the University of California, sooty mold can be a variety of different fungi that don’t necessarily infect plants, but that harm them by blocking sunlight penetration. This mold tends to black as the name suggests and it also tends to look like a layer of black dirt. There are 2 ways you can remove or decrease the effect of sooty mold: 1) wash away the mold from the leaf and 2) prune away the affected leaves. I tried gently removing the mold from my plants’ leaves with soap and water, but this only worked up to a certain point. Eventually, I found I needed to prune back much of the infected leaves and wait for new growth. During the winter I noticed that the sooty mold was not only on my plants, but it was also on my pots, tables, and shelves. In order to prevent the mold from spreading, I gave my patio a good scrub down with warm water, dish soap, vinegar, and orange and lavender essential oils. So far this spring I haven’t seen the sooty mold make a reappearance.
Now that the spider mites, aphids, and sooty mold have been cleared up, I’ve been busy planting new bulbs, repotting my plants, and traveling to botanical gardens. Next on the blog we’ll revisit the Atlanta Botanical Gardens’ Orchid Daze and the US Botanic Garden in Washington, D.C. then we’ll talk about effective ways to store your bulbs and seeds as well as what I’ve got growing on my patio. Also don’t miss the newest feature: plant baby spotlight.
Do you have questions about your plant babies? Are you having trouble with pests, root rot, or finding the right planter? Are you excited about learning more about house plants, cacti, succulents, or container gardens? Leave a comment below or feel free to contact The Garden Generalist. I would love to hear from you!
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9 thoughts on “When Aphids (& Spider Mites) Attack!”
Used your method with the rosemary oil today on several plants that had to be brought in for the winter. How often would you say I should use the mixture on them? In particular, 3 of them are species of coleus, one is a type of begonia and then there’s an african violet.
Hi, Accidental Gardener! Honestly it depends on your aphid/spider mite infestation. For example— If you have a large, widespread infestation on your coleus and begonia, I would apply twice daily using a cloth dampened with the rosemary oil mixture to wipe away the aphids instead of spraying directly on the plants because of their leaf texture. If you’ve included neem oil in the mixture I would suggest keeping your plants out of direct sunshine because using neem regularly on leaves causes photo toxicity and the leaves will burn more easily.
The African violet is a little more tricky. Mine typically don’t like excess water on their leaves so when I had to treat them for mites it was more of a challenge. My infestation wasn’t bad, but I still applied the rosemary solution using a q-tip to the infected areas daily. Spot treating helped keep damage to their little hairy leaves to a minimum. When the infestation started to escalate I wiped away any mites when I saw them using a lightly solution dampened cloth once daily.
If you have other house plants I’d suggest keeping your infested plants isolated from them. Aphids and mites tens to spread quickly especially inside.
How often should it be necessary or could I assume the problem is irradiated if I don’t see any more of them around the surface the plants sit on? They won’t be going back outside until it’s warm enough for them to survive.
Not knowing the extent of your infestation I would say start with once daily and if you don’t notice improvement move to twice daily, etc.
Aphids like the bottom of leaves to live and reproduce, so once they’re gone from both sides of the leaves then you should be fine. Aphids leave a sticky spittle on leaves and sometimes on containers so be sure to wipe them down otherwise you might get mold.
I just moved into a duplex and I realized today that the rose bushes on both sides of my front door and my neighbor’s front door are wildly infested with what I believe to be aphids. They’re little green bugs and they are absolutely COVERING every single new rose bud that hasn’t bloomed yet. The rose bushes are about 4 feet tall and 2 feed wide. So….big….
A few days ago I planted alyssum, snapdragons, and some dianthus near the rose bushes and I’m afraid they will become infested as well. My question is can I treat such large rose bushes that are so heavily infested with the natural method you’ve outlined or do you think the job may be too big and I need to go straight for the miticide?
Wow that sounds like a crazy infestation! I’d suggest trying to treat the plant with a gentler solution first. I’ve found that a combination of dish soap, rosemary essential oil, neem essential oil, and water mixed together is best for aphids. The dish soap helps to remove the oily outer layer of aphid bodies so that over time they dry out and die. An insecticidal soap will do something similar in addition to poisoning them. Rosemary is a natural insecticide/ disinfectant while neem is a natural fungicide. I use rosemary essential oil to repel aphids and other nasty bugs and I use neem to deter the growth of fungus where the aphids have been snacking on my plants. Aphids leave behind a sticky “dew” after feeding which can led to black mold growing on the “dew” and your plant. It’s a bit more of a holistic approach.
In addition to using the spray to kill the bugs I think you would also benefit from giving your rose bush a bath. I know it sounds crazy, but if you can see that your plant is absolutely covered in aphids, physically removing them will help your odds of your plant surviving. Mix the above solution in a bucket and wipe the plant down with a cloth until you’ve wiped away the aphids you can see. Then give the plant a good spray and leave to dry. Spray the plant every other day for about four days then once every two days. Spray any neighbouring plants lightly to prevent infestation once every two days as well. Aphids are like a common cold in that they spread like crazy if not kept contained.
If your aphids come back after a week then I’d suggest going for an insecticide to finish them off.
Hope this is helpful!
The Garden Generalist
Hi Sofia I live in Sydney Australia and have been reading your advice on aphids and spider mites.
Your shared knowledge, experience and tried and tested advice are very much appreciated.
I’m feeling very positive about solving my infestation. Thank you for sharing . Kind Regards
Hi Virginia! Thanks so much for your kind words. Best of luck with your infestation! Best, Sofia