When it comes to gardening, Florida holds its own as a top contender for “most garden problems happening all at once.” Our climate, especially in Summer when it’s hot and humid, is the perfect place for pests to go unchecked and to thrive.
From the suggestion of newsletter reader Gabrielle, as well as several customers bringing me a leaf to ask me what’s happening to their plants (quite recently, in fact), I’ve begun a series about common garden problems! It’s mostly aimed at beginners, but I’m hoping it will be enriching to all. You can let me know what you think in the comments or email me! I’d love to know what you want to know about!
Aphids: What Are They?
Aphids are small insects that are sap-suckers, which means they bury their mouths into leaves and stems and remove the plant’s fluids. They operate similar to ticks in that way, except that during certain phases, they can fly and move to other plants. Ugh.
Close-up of aphids on a stem. Note the different sizes, colors, and forms of aphids, from very young, to larger older ones, and the one with wings!
Aphids are a very ancient insect, dating back to the Permian period. As plants diversified, aphids specialized and adapted, and now there are many many different kinds! So many, in fact, that they have their own “Superfamily” called Aphidoidea. Say that word 5 times fast.
Why are Aphids on my plants?
A very good question. In short, the answer is this: Your plants are delicious. No really! Plants use sugars to conduct their business of living, and aphids are really hungry. Like, all the time. They never really stop eating.
In small numbers, you hardly notice them. Aphids are only really destructive to plants when they congregate in huge numbers (like in the picture above), and can kill a plant when the plant is overrun and can no longer sustain photosynthesis due to lack of fluids.
When their host plant dies, they move on to another either by walking to a plant that is touching the one they’re on, or some of the aphids have wings and fly to the next.
Females can reproduce about 200 babies at a time, which can overwinter in eggs too if it’s too cold to hatch OR they can birth live babies too! They can reproduce sexually or through parthenogenesis (basically the biological equivalent of natural CLONING, see Thelytokal Parthenogenesis). Talk about adapting!
Just a few of the many types of aphids…the white one is appropriately called a “wooly aphid” and I know that these are sometimes mistaken for mealy bugs! It’s hard to tell the difference.
What Does Aphid Damage Look Like?
There are several characteristics to the look of aphid damage. They can occur in any combination! Let’s look at them a bit more closely.
Aphid Damage A: Leaf Dots
Early Aphid damage appears as such. Lower image courtesy of UF IFAS here: https://plantpath.ifas.ufl.edu/u-scout/tomato/aphid-damage.html
Silver spots on the top will show up on the underside as holes in the leaf underlayer where aphids were (or are). Those spots are weak and become brown, and then they become holes in the leaves as the plants try to protect themselves by “jettisoning” the damaged cells (it diverts resources from the damaged cells!).
Aphid Damage B: Leaf Blight
This is moderate to severe aphid infestation. Notice the yellowing in large parts of the leaf in the foreground, and behind that, leaves that are fully compromised. Photo credit UF IFAS (same as the previous image)
Leaf blight is a more advanced form of the leaf spot. At this stage in the “intermediate” infestation, large swaths of the leaves are turning yellow as the plant fights to keep fluids in the leaves and continue photosynthesis and the aphids keep draining the plant’s lifeblood – like little tiny vampires.
Eventually the aphids will damage the leaf to the point that the plant will have to cut its losses and eliminate the leaf. Sometimes the whole branch. Aphids just move on to the next leaf, or stem and continue the carnage!
Aphid Damage C: Leaf Curl
Leaf curl happens as the leaves lose fluids from the incessant sipping by the aphids. Unable to achieve the proper osmotic pressure to hold the leaves out flat and catch the sunshine, the leaf curls in on itself.
Different kinds of leaves curling from hungry aphids.
Leaf curl is usually one of the first major signs of aphids, as it’s easy to miss a few brown spots and small leaf holes from early infestation. When you see leaf curl, it’s serious.
One of the benefits of leaf curl, from the aphids’ perspective, is that it provides shelter from detection, rain, hose sprays, insecticides, etc. When you are treating plants with leaf curl from aphids, consider removing those leaves. At the very least, uncurl the leaves manually and individually as you spray if they cannot be removed.
Aphid Damage D: Severe Dessication
Dessication is the removal of all water from something. Think: MUMMIES.
Pea aphids stopped these plants from producting seed pods by the time harvest rolled around. Notice the complete dessication. Source: Researchgate
Hopefully you’ll see the damage and fix it before it gets to this point, unless you’re just letting that plot go fallow or allowing the plants to run their course.
I highly encourage you to take care if it before it goes this far, as the aphids can spread to other things you care about. They also bring with them other problems that you don’t want. That’s in the last section of this article! First, let’s see what to do about your aphid problem.
So I Have Aphids, Now What?
Now we get to the nitty gritty: What to do when you discover aphids on your plants.
Many people swear by a strong spray of water to knock them off the plants. This definitely works if you discover just a few of them on your plants. You can use something like this.
Insecticidal soaps are another go-to for gardeners, especially gardeners focused on food crops in the backyard. Soap sprays coat the aphids and disrupt their body coverings, basically dehydrating them. When you use sprays like this you must get the undersides of the leaves as well as the tops, and the stems too. It may take several treatments as aphids reproduce VERY quickly.
Another treatment is some of the oil-based sprays, such as Neem oil, or Parafine or Horticultural Oil. Oil sprays coat the aphids and stick to them, and they suffocate. Again, these oils are often used by food crop growers, and Horticultural Oil is heavily used in the Citrus industry to treat all kinds of pests.
Aphids are part of the food chain. This ladybug is eating aphids! Another insect relies on aphids too – ants farm aphids like cattle and eat the “honeydew” excretions from the aphids (which is basically sugar water!).
Encouraging natural predators is a great and safe way to control aphids. If you’re willing to allow some of your leaves to be sacrificed, aphids attract predators such as ladybugs (we carry them on a limited basis! Call us!), lacewings, midges, hover flies, damsel bugs, soldier and blister beetles. Additionally, certain parasitic wasps lay their eggs in aphids, and their larvae consume the aphid from the inside out. All of these insect friends are good to have around!
Next we have organic and non-organic insecticides, which are mostly non-discriminatory and will kill all the insects they touch. A popular organic insecticide is Conserve Naturalyte, with its active ingredient Spinosad. A popular non-organic insecticide is Sevin spray (or dust), which is Carboryl.
Other Problems Caused By Aphids
As if having the aphids wasn’t hard enough, actually having an aphid infestation causes other problems too. Let’s explore this!
Ants
Ants love aphids. I, for one, appreciate the role that ants play in the environment – the clean up service! But when I’m trying to pick green beans, I don’t want them biting me. Why would ants be biting me from my green bean plants? Well, if my green beans have aphids, the ants are there to “farm” the aphids.
Humans aren’t the only creatures clever enough to farm cattle.
The ants use the “honeydew” secretions from the aphids as food. Honeydew is basically sugar water, and ants need energy that the sugar provides. Ants have figured out that if they keep aphids as cattle, then they have a constant energy supply right at their front door.
And we thought we were the only clever ones here on Earth.
Sooty Mold
Sooty mold is a byproduct of aphid secretions mentioned above. When aphids are abundant, so is their waste. That waste is made of sugar and water, which is a perfect breeding ground for mold!
Sooty mold: It’s ugly, and it can sometimes keep your leaves from “breathing” properly.
Sooty mold can be harmful if it is coating all surfaces of the plant, but most of the time, it just affects a few leaves here and there, and it’s easy to wipe off.
But it is a GREAT way to easily see when aphids are around. Sometimes this mold is your first sign that you have an aphid problem, so when you see it, definitely look for aphids.
Once you treat for the aphids, the sooty mold should abate itself unless you’re in a very wet and shady area. Then you’ll probably need a fungicide like Garden Friendly Fungicide (an effective organic option).
I hope this article helped you identify and treat some aphid problems you might be having in your yard or garden. In the next blog I’ll continue with some common questions about pests that we get asked to identify here at Shell’s.
Until then, Keep Growing!
Marissa
P.S. I was serious about making requests on what you want to learn about – ask away!