My friend once described leaf aphids as small sesame seeds that sit on the bottoms of leaves and along stems, sometimes on the bottom of the plant and sometimes on the top. This is such a perfect description of these little insects! As a gardener/plant caretaker, you really want to watch out for them because they can destroy plants fast. They take on the color of what they eat (which seems to give them an element of camouflage), typically they are green, white, yellow, orange, or black. Leaf aphids can't fly in their adult stage, but there are root aphids that live in the soil and in their adult stage they can fly. All aphids are to be watched - none of them are a gardener's friend.
They suck the sugar out of your plant and poop it out as a sugary substance knows as Honeydew. You can usually the a sheen of sugar on the top of the leaf indicating that aphids have been pooping on your plant! You may also see yellowing leaves from the bottom of the plant up, deformed growth on flowers and leaves, and more.
To top it off, in the fall they breed extremely fast - the females don't need males so they reproduce constantly. They are only harmful in large populations, but they breed so fast that they can quickly become an issue. Ideally, you can prevent the issue with a few simple measures in place.
I guarantee you that being proactive as a grower pays off! Here are a few ways you can do that:
Keep up on general cleanliness in the garden as best you possibly can.
Maintain high standards of plant health. Keeping your plants healthy and strong can prevent infestations just like staying healthy keeps you safe from certain diseases. Also keep them pruned so that they have a lot of air flow. Dead and yellow growth isn't helping the plant anymore and should be removed.
Use yellow sticky traps to indicate if there are any insects present in the garden. If you see a few on a sticky trap you can be certain there are many more.
Spray all organic insecticidal soap. It protects your plants from many insects and is very safe to use. I don't like using neem oil because it leave a residue that can harm beneficial insects and pollinators.
Ok, let's say you tried all of those things and still got aphids (or maybe didn't find this blog early enough to try to prevent them). Here are some action steps that you can take when you see them in your garden:
Make sure you are implementing everything from the preventative list above (cleanliness, healthy plants, trapping insects, and insecticidal soap). Once you have established that baseline you can move onto other treatments.
Go in and take all the leaves off that are infested with aphids. They like to sit on the underside next to the veins. I also like to grab the stems they are sitting on and smash them between my fingers. It is gross but your plant will appreciate you!!
Again, make sure there is a ton of air movement in the plant. Aphids typically don't like air movement on them. If outside this can be done by training the branches of a plant apart so there is air space and pruning off extra growth. Inside you can do the same training and pruning, plus turn a fan on directly at the plant.
Use biological controls to combat the population. Using predatory insects or fungi can naturally reduce the population of aphids without hurting your plants or the environment. You can order these online, I always order from Arbico Organics at www.arbico-organics.com. They are super knowledgeable and helpful if you have any questions about using them.
Also, Arbico Organics has a ton of information on their website about different pests and how to control them. Here is a link to the section about Aphids. I got a ton of good information from them when I was fighting aphids on my plants.
Good luck and be sure to act fast and frequently when dealing with aphids. Watch their population and make sure to act BEFORE it grows in numbers drastically. Read up on Arbico Organics and see what you can learn about aphids and other pests.