When Aphids (& Spider Mites) Attack!

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:

  1. there are no natural predators like lady bugs or lizards to eat and control them, and
  2. 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.

 

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Signs of both spider mite and aphid infestation include discoloration of leaves. Pictured here is parsley that was infested with both spider mites and aphids.

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.

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Aphids are much bigger and therefore much easier to see than spider mites. Pictured here is a Gerber daisy that is infested with aphids. If you look closely, you can see their yellow-green bodies in the middle of the leaf.

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:

  1. 10 drops of rosemary essential oil
  2. 3 squirts of dish soap
  3. 1 liter water
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Once spider mites and aphids infest a plant, the damage done to the leaves can cause other problems like mold. Pictured here is what I believe to be sooty mold on my gerber daisy.  

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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