Aphids feed on plant sap. If there are too many of them, leaves can curl, become deformed, or change colour. That's what insect researcher Anders Endrestøl from the Norwegian Institute for Nature Research says.
When leaves curls, they create the perfect hiding place for aphids.
Some aphids go directly for the fruit on fruit trees and ruin the quality. Others drink from stems and buds.
Annonse
Stressed and weak plants are particularly vulnerable to attacks, says Endrestøl. So it's important to keep your plants healthy and well-fertilised.
Sticky residue and fungus
When aphids drink the sweet plant sap, they secrete a sweet, sticky substance called honeydew.
If you've ever parked under a linden, you may have noticed your car has a sticky layer on it. Blame the aphids.
Honeydew can lead to fungus on the leaves. It doesn't look particularly nice, but worst of all is that the plants have trouble with photosynthesis. This can result in poorer growth. The upside is that honeydew and fungus can be washed off.
On rose bushes, aphids can cause poor growth or deformed flowers.
The two-spotted ladybird is a cute and helpful caretaker in the garden.(Photo: Shutterstock / NTB)
Crush and scare?
Many people put on gloves and crush them. This might also have a side effect of scaring other aphids away from the area.
"They have little 'exhaust pipes' on their backs that release alarm chemicals," says Endrestøl.
Aphids are social creatures, and as you've probably noticed, they live close together. It makes sense that they send signals to each other. The problem for plant owners is just that the aphids cannot flee very far.
Most of them are wingless for most of the year. They can only flee to other parts of the same plant.
Be glad if you see this caterpillar! It eats aphids and becomes a ladybug that also feeds on aphids.(Photo: Shutterstock / NTB)
Only in the autumn do aphids explore the world by air. That is when they find a suitable plant to lay their eggs on. This ensures next year's aphids population.
The aphids on your rose bush, birch, or plum tree this year likely come from last year's eggs. But Endrestøl emphasises that this varies between species. Around 350 aphid species probably exist in Norway. They feed on different plants and have different lifestyles. They have been poorly studied, so there may be species that haven't been discovered yet.
Complex creatures
Annonse
But aphids have another way of reproducing besides mating between male and female. Females can give birth to large numbers of offspring entirely on their own. This is called parthenogenesis.
Reproduction and wing development in aphids are more complex than they seem.
And completely eliminating aphids from a rose bush? That’s not realistic.
"I think you can forget about that," says Endrestøl.
Because of their ability to reproduce without mating, a single surviving female is enough to launch a whole new colony in a short amount of time.
"It goes incredibly fast when conditions are favourable," he says.
Create a predator-friendly garden
It might be tempting to reach for pesticides, but doing so could harm beneficial insects you actually want in your garden – like ladybirds, one of the aphids’ natural enemies.
So maybe the goal should be to attract ladybirds into the garden?
"You can help make that happen. Hoverfly larvae are also predators that eat aphids. If you have a flower meadow in your garden, you'll support a wide variety of insects, many of which are predators. Not just aphid specialists, but general predators that also eat aphids. It's smart to think in terms of biodiversity," says Endrestøl.
A single larva can eat as many as 500 aphids during its larval stage, according to an article from NIBIO. So if you’re lucky enough to have a few in your garden, they can make a big difference.
Hoverfly larva on the hunt for aphids.(Photo: Hallvard Elven / Natural History Museum, University of Oslo / CC BY 3.0)
Gentle chemicals and leaf removal
If you want to take matters into your own hands, there are plenty of home remedies against aphids. Green soap and vinegar are the usual go-to options.
"Green soap can penetrate the aphid's respiratory system. That can reduce the population," says Endrestøl.
Some recipes include rubbing alcohol, which can also be effective – just be cautious with the dosage. Too much can harm the plant. Experiment carefully and follow tips from others who’ve had success, the researcher advises.
You can also manage aphids by hand. Squeezing them is one way, but there are other simple tricks:
"I have a cherry tree that struggles with aphids, and I simply pinch off the leaves that are most infested. The tree quickly grows new ones," he says.
