Warning: This is not for beginners. If you like the “squirt squirt” of a spray bottle, don’t even read this.
I’m in a unique position working with aphid and other plant pest control in commercial crops. With my experience comes an understanding/tolerance for pests: I can tell if a pest population is something to worry about or if it is something that will go away on its own.
After engaging in all sorts of gardening blogs and communities it has become a major concern that most people react immediately (and sometimes inappropriately) to the sight of “bugs” on their plants. Furthermore, when someone says “aphids killed my___” (or any pest for that matter) I tend to cringe, knowing that pests rarely kill (except seedlings) but instead pests are most often a symptom of a problem elsewhere. For example: The Cabbage aphid on brassica is a direct result of high soil temperatures and usually exacerbated by soil more acidic than optimal.
So I want to share a strategy I use, which also illustrates my position on aphids: I put aphids in my garden.
Again, I want to say “Don’t try this at home,” but for many of you seasoned growers you could.
Here are some specifics to get out of the way:
Timing: I am not adding aphids to my yard in a wet May when they will find optimum conditions. I am adding them early in the season when their growth is slow.
Species: I am using a red-phase green peach aphid. I know it’s host range, it’s temperature preferences and its natural predators.
Source: I have to keep an aphid colony for work purposes, so these are easy to come by.
Here’s some background:
I scout, and scout constantly. My wife hates my “aimless meandering in the garden,” but walking by and looking at plants will condition you to get to that point where, from across the yard, you can spot a leaf that “doesn’t look right.” So I do this, and in my first year in my current garden I did this and I found some plants that host aphids very early some years. Sometimes as early as March. Instead of removing them, I checked on them every couple of days. Their populations got bigger…and bigger….and….then they were gone. All that was left was the “mummies” of the aphid-parasitoid wasp, Aphidius.
I do this regularly just to see what natural predators show up. In fact, I did this one year, found a hoverfly species that wiped out large aphid colonies and commercialized it in partnership with the University of Quebec! You can buy the American Hoverfly from our retailers and distributors here.
However, adding Aphids came about because of this: My first year growing hops was an exercise in pest control. They got aphids, they got spider mites and I watched natural predators slowly overcome the pests. (On fast growing plants, pests are usually at an advantage.) The following year, an Oregano near one of my hops was absolutely covered by tiny green aphids on the undersides of the leaves. But, there were also hundreds (literally) of hoverfly eggs and larva of different hoverfly species eating those aphids. I left it and watched as the plant eventually was spotless a few weeks later. That entire season, the hop never got aphids.
This made me consider: What if the early establishment of predators limits the pressure of aphids for the rest of the year.
And so began a multi-year trial and now a regular gardening practice of mine, which I’ll now share.
Year one: I took a 5 foot tall Tobacco plant covered in my aphid and planted it directly next to tomatoes. I did this next to tomatoes because they are in the same family, so the aphid could transfer, but this aphid prefers tobacco over tomatoes, so only if the population overcame the tobacco would there be a full-scale migration to my crops. Instead, I anticipated a small spread of aphids, but not before the predators showed up.
To my surprise, the aphids immediately formed aelate (winged) individuals and spread to other plants in the yard, like brassicas. But, as I predicted, the tobacco started to recover as spiders, lacewing and hoverflies regularly began feeding on the aphids. The aphids did explode on the brassicas, and the hoverflies and aphidius were a week behind in finding them, which made me sweat a little, but eventually there were all cleaned up. Whether or not the predators stuck around, I know that my trial produced hundreds, if not thousands of aphid predators that would have to go find more aphids elsewhere.
Year two: Peppers are more favoured than tobacco by my Aphid. So, I grew peppers and allowed them to get the aphid. Unfortunately, in our climate, peppers are slow and the aphids do some serious damage, distorting leaves and stunting or killing growing tips. So I had some ugly peppers. However, my goal this year was to do the opposite that everyone else does…try and keep the aphids alive. So, I did everything aphids love; I used water soluble fertilizers (miracle grow) and kept them warm and humid. I did not enclose them in a green house (which would have prevented predators from finding them), however. Sure enough, despite the conditions, the aphids were eradicated, and quickly.
Also year two: My roses get a green aphid on their buds in Spring. They can do damage to the flowers if given the chance. So, instead of fighting THOSE aphids, I put my green peach aphid (probably not the same species) on my roses before it flowered. They established on the rose, and so too did the predators and the rose was cleared of aphids. Did the native aphid show up a month later….no.
Year three: I loaded the peppers with aphids. I actually grew them in our “aphid house” where there is nothing but plants and aphids and they multiply quickly. Then I moved them to my cold frame, which is open via vents, but otherwise sheltered (and more or less enclosed at night). Fortunately it was cold, so the aphid growth was slow, because no predators showed. I started to panic a bit because I planned on reusing the peppers for my actual garden. So, I simply moved them outside during the day. Sure enough, a few days later…… hoverfly eggs.
We know that many aphid predators find aphids via the smell of the honeydew they produce (Aphidoletes). Others may need to find them visually (hoverflies), while most of the predation seems to occur at night (lacewings and spiders). We also know that most predacious invertebrates will eat aphids if they come across them.
So why the big problem with growers and aphids? First, in a greenhouse, there are no natural predators, so you need to introduce them. But for a garden and yard, are aphids ever actually a problem? Well, yes. Nature has a balance. Aphid predators need lots of aphids in order to feed themselves and guarantee another generation, so typically, aphids emerge and attack plants earlier than the predators arrive in order to build up large aphid populations to feed all the “good” bugs. This is why big trees, like Lynden trees start dropping honeydew from millions of aphids in the summer (on your windshield), but thousands of ladybugs and other predators will clean the plant off by the end of August (if people didn’t panic and spray the tree). So Aphids can have the upper hand. And if you’re growing a plant out of its comfort zone that is susceptible to aphids you’ll see lots of aphid damage before the predators show up. We need to be aware of this “threshold.” When aphids are too much for you, you will act. So if the predators are slow, you won’t be happy. The solution: invite aphids earlier to other plants. But, that’s only easy if you have aphids early…
Since you don’t have access to aphids like I do, (nor will I sell a plant pest to you), the absolute best solution is to provide other plants aphids are drawn to, and leave them alone. Don’t be quick to wash aphids off a plant or use any “natural home remedy” (all of which kill predators too). When one brassica gets aphids, don’t pull it so that it “doesn’t infect the others.” Leave it. Let them try to kill that plant (since you were about to anyways), and let the predators lay eggs and reproduce. All brassicas will get the aphid, but they’ll survive and be fine when cool weather returns in late summer. You probably already know which plants get aphids first. Try growing another of the same plant in a place you won’t care about it as much and let it be the Aphid trap and Aphid predator bank.
If you’re really brave, try looking for aphid predators on leaves, removing the leaf and placing it on a plant that has aphids that you want to protect…..which is exactly how people used bio-control for the last thousands of years outside of the last couple hundred. This process is still used in many commercial crops like peppers. If they see spider mites and a predator (persimilis or fallacis), they remove the leaf and move both the spider mites and predator to an area where they found spider mite without the predator. Makes sense, right?
So, consider this your masterclass in aphid farming. Now go out and watch your aphid colonies. I can almost guarantee anything you see amongst the aphids that is not an aphid is an aphid predator. And I can almost guarantee that once you see one predator, there are many and your aphid colony will be short lived. If you want to take this a step further – consider yourself promoting the health of your garden by promoting aphids and therefore their predators. (There are other ways to promote beneficial insects as well.)
If you get nothing else out of this, please know this: It is extremely difficult to keep an aphid colony alive. They will always get eaten. The more aphids you have the more attractive they are to predators. If you can tolerate their presence, just leave them alone. They’ll be gone before you know it.
Good luck, and happy Aphid Farming!
Even “organic” sprays or “home remedies” are worth avoiding. Anything that kills or dissuades a pest from a plant will be doubly as effective at killing or dissuading the predators. Any soap or detergent, acid or base can kill insects, but it will also strip the waxy coating off the leaf’s surface that protects it from infection, UV and insects. A few days later, pest will return but the predators will not. Some of them detect aphid colonies by the type of light reflected from plants that are chemically responding to pest pressure. When those plants respond to physical and chemical damage from “home remedies” they sometimes won’t be recognizable as a plant with pests. Further more, very sensitive predators like Aphidoletes, will never again land on a plant that has been exposed to soap. It is believed this is because it affects their sense of smell. Neem oil will kill everything, including the good bugs but has little effect after it has dried except to deter predators that search by smell.
Some aphid species are worse than others. Several “black aphid” species have an enormous host range. And you’ll see them go from plant to plant in your yard over the course of the year. Fear not, they are just moving to keep ahead of their predators. Go look at where they have been and you’ll see the predators or signs they were there.
Fast plant growth feeds aphids. If you fertilize your plants with a water soluble fertilizer or load up the nitrogen, you will have a struggle with aphids. Remember, plants don’t want to grow fast, they just have to when you give them fertilizer. This makes their tissue softer and more susceptible to infections (molds and mildew) and sucking insects (aphids, spider mites…etc). If you regularly feed plants that get aphids, try skipping the feeding one year. The leaves might not be as dark-green, but they’ll be happier and your plant will have to send roots deeper to look for nutrients (making it healthier).
Predators are massively restricted by air-flow. If it is windy they’ll do nothing until the wind stops. So if you have a greenhouse and fans…turn the fans off if you need to improve predation.
All chemicals hurt predators. “Compatible” pesticides/herbicides/fungicides just mean they don’t kill some predators immediately. But they can kill them slowly or give them non-lethal effects like sterilization or blindness. When natural predators have failed to control aphids it is (every-single-time) because some chemistry was applied. I’ve seen it fail when a grower sprayed something to kill moss on the walkways (which wasn’t listed as a pesticide); I’ve seen it fail when a water surfactant was used (so there were no water spots on their cut flowers); I’ve seen it fail in Cannabis because of “compatible” sprays for mildew. So, remember this: either grow Organic or plan on introducing predators after every chemical application.
Know your Bugs: