For several weeks I've noticed a glistening on the leaves of weeds, trees and wildflowers as I walk in the field. It's not everywhere — just here and there, on one plant or another, especially sunflowers. At the top of the plant, there's a sheen that looks as if it's been spritzed with a light salad oil. The lower leaves are covered in what looks like black soot.
These are sure signs that aphids are ballooning in numbers, and they've spread to a few of my pepper plants, eggplants and melon vines.
Aphids can be found in any healthy garden. They're not a sign that something's wrong. To spot their tiny soft bodies on the underside of a tomato leaf or clustered on the budding leaves of a pepper plant is normal. Mature, healthy plants can handle aphids just fine.
Having a few aphids on each plant is a sure way to keep beneficial insects around, because they're food for ladybugs, praying mantises, lacewings and other predatory insects that you want living in your garden. A balance between predator and prey can help maintain healthy crops. When the balance tilts toward the plant eaters, you sometimes need to get involved and bring things back to an equilibrium.
Something about the weather this year has favored aphids, and they're outpacing their predators.
Something about the weather this year has favored aphids, and they're outpacing their predators. Of 20 pepper plants I have in a hydroponic setup outdoors, two have become infested with aphids, although the rest are untouched. These two have been a little stunted since I planted them and were therefore susceptible.
The same goes for my eggplants; a couple were overtaken with aphids. That a couple of plants can be affected by aphids while the neighboring plants show no sign of problem confirms observations many growers have made that aphids have a way of taking out the weaklings.
In most cases when such a low-threat insect begins to kill a plant, I let it. I always plant more than I need anyway, because something will kill off a few plants each season no matter what. Sometimes it's improper watering, or I accidentally break it off at the roots when I'm weeding. When it's an insect that threatens a few plants, I've found that those plants would have needed more intensive care than they're worth, so the aphids are doing me a favor.
But not this time. Because my hydroponic setup has space allotted for a set number of plants, losing a couple would mess up my configuration and waste garden space that I've put effort into making flat and weed-free. I want the maximum harvest I can get from this well-tended square footage. So I decided to take steps to spare these plants from their demise.
Aphid hose down
There are plenty of pesticides on the market for taking out aphids, even organic ones. The problem with all of them is that they don't just kill aphids — they kill everything.
Fortunately, the most effective non-toxic control for aphids flows cheap from the garden hose.
Using them to kill aphids, I would also kill the bumblebees that ensure that my peppers are pollinated. I'd harm the spiders that have been gorging themselves on every other plant-eating insect. I'd kill off the toad I spotted in the beam of my spotlight as he hopped among the pepper plants one night in July.
I'd also be killing a reliable long-term aphid solution: the ladybugs that eat aphids all day and night. They're just having trouble catching up with the numbers this year. The solution I choose has to avoid making it even harder for the ladybugs or else I'll be stuck with the task of controlling aphid numbers all by myself, with no allies to do any of the work for me.
Fortunately, the most effective non-toxic control for aphids flows cheap from the garden hose. A strong blast of water over and under each leaf on an affected plant amounts to near total eradication of aphids. The insects are soft and weak, so dislodging them from a leaf is easy enough.
Once they've been sent on their way, they'll never come back. For those that find a way to hold on, the water drowns them, especially if it's mixed with any brand of plant wash or insecticidal soap.
Plant wash is a mild soap that, when added to water, creates a solution that won't harm plant leaves, as homemade concoctions often will. It's slightly sudsy, and when these suds bathe a small, soft-bodied insect, it either suffocates or is desiccated by the soap as it dries out, like how washing your face makes it feel taut and dry.
In a mild enough mixture, the plant wash won't harm hardier insects such as ladybugs, so it's targeted to aphids. Because I've decided to forego all insecticides that work by poisoning insects, plant wash has become my one of my only resources for nudging the balance of prey and predator back in balance.
Plant wash is a mild soap that, when added to water, creates a solution that won't harm plant leaves
To blast the mixture onto affected plants, I use a pump sprayer, a plastic container with a pump that compresses air inside the container to pressurize the mixture. I attach a spray wand with a trigger to the container by a hose, so I can direct the high-pressure stream of water and plant wash in any direction. The undersides of leaves must be sprayed as much as the side that faces upward.
When people tell me that plant wash doesn't work, I find that they use it like a chemical insecticide, spraying just a mist in the vicinity of the plant and imagining that it will kill just like the chemical nerve toxins in chemical insecticides do. They think a puff is all it takes.
But to use a plant wash, you have to get close to the plant, grab the stalk and spray it down, as if you were washing mud out from under your fender at a DIY car wash. I grab clusters of leaves and spray them off, watching the aphids, the honeydew they exude and the black sooty mold that grows on the honeydew wash off in an instant.
I pay special attention to clusters of leaves that bud out at the tips of a branch because they're especially hospitable for aphids escaping direct sunlight. I spray up and down the stalk and out to the ends of each branch, hitting all the surface of the plant with the jet stream emitted by the spray wand.
It only takes a couple of minutes to wash off each plant, and the result is a plant that looks immediately greener, healthier and shinier. The next day, the leaves lose the curl that results from having their juices sucked out. Within a week, treated plants will have new growth.
In my most recent use of plant wash, I sprayed down eggplants that were almost black from mildew growing on the honeydew that the aphids had dropped onto the leaves under them. Although it's harmless to the plant, it still indicated that there were too many aphids for it to thrive.
I worried I might hurt ladybugs that I may have missed in my inspection of the plant before treatment. But on the following day, I found ladybug larvae, pupating ladybugs and adults all doing well. I hadn't seen them before, but after the treatment, there they were, unharmed and eating a few of the aphids that had made it through the deluge.
For the last two summers, I've used both a water-only spray and a mixture of water and plant wash to treat hydroponically grown crops, which are more susceptible to aphids because of the high nitrogen nutrients applied to them. Both times, one treatment was all it took for the whole growing season. The plant wash mixture works a little better than water only, but only slightly. Both are harmless to bees and butterflies. Toads seem to enjoy the change of weather.
When we must step in to ease a natural balance back into shape so we can grow our artificial crops, it makes sense to do so in a way that doesn't throw a bunch of other balances into chaos. Aphids are not something to get rid of in the garden — just something to keep an eye on and wash off vulnerable plants if the ladybugs are overworked.
Yellowing leaves and sooty mildew are sure signs that aphids are thriving.
