Why Experts Say Not To Use Pesticides On An Apple Tree Woolly Aphid Infestation
Elizabeth is a Permaculture Garden Designer, Sustainability Consultant and Professional Writer, working as an advocate for positive change. She graduated from the University of St. Andrews with an MA in English and Philosophy and obtained a Diploma in Applied Permaculture Design from the Permaculture Association.
Reviewed By COLIN SKELLY
Colin is a Horticulturist and Horticultural Consultant with experience in a range of practical and managerial roles across heritage, commercial and public horticulture. He holds the Royal Horticultural Society’s Master of Horticulture award and has a particular interest in horticultural ecology and naturalistic planting for habitat and climate resilience.
IN THIS GUIDE
If you see a white fluffy substance on your apple tree, you may at first suspect a fungal problem.
However, what can look like a whitish mould or fungus is more likely to be a sign that your apple tree has a woolly aphid infestation.
A white waxy fluff or fur-like substance on apple trees is excreted by small sap-sucking insects known as woolly aphids.
They excrete this substance that gives them their characteristic woolly or furry coating in the spring and summer months, when they begin sucking sap from beneath the bark.
What Is Woolly Aphid?
Woolly aphid is the name given to the insect Eriosoma lanigerum.1Lordan, J., Alegre, S., Gatius, F., Sarasúa, M. J., & Alins, G. (2015). Woolly apple aphid Eriosoma lanigerum Hausmann ecology and its relationship with climatic variables and natural enemies in Mediterranean areas. Bulletin of Entomological Research, 105(1), 60–69. https://doi.org/10.1017/s0007485314000753
It is a sap-sucking bug found only on apple, cotoneaster and pyracantha trees and shrubs.
On other plants, a white waxy deposit can be a sign of scale insects, other aphids, or mealybugs in greenhouses or polytunnels, but when white fluff is seen on an apple tree, the woolly aphid is the most likely culprit.
Woolly aphids spend the winter on apple trees as nymphs that hide in fissures in the bark or in the crevices of branches.
In spring, these blackish-brown sap-suckers become active again, concentrating their efforts where the bark is thinner and around old pruning cuts.
They start to suck sap from the tree and begin to excrete the woolly white substance.
By the middle of summer, the population of these insects will often have increased and the insects will often spread onto new, younger shoots.
Soft lumpy growths will often develop in the bark of these shoots as the woolly aphids feed, due to chemicals excreted by these insects into the bark.
In mid-summer, winged forms of these aphids will then develop, and these will then fly off to search for new host plants to colonise.
Is It A Problem?
The first thing to understand as an organic gardener is that woolly aphid should not be viewed as a problem per se, but rather as an integral part of the garden ecosystem.
Like other aphids, these creatures are a food source for a range of wildlife and even pest species can be crucial in maintaining natural biodiversity within a space.
Get rid of aphids altogether and you will also get rid of the diverse life that preys upon them.
Reduced biodiversity can reduce the resilience of the system as a whole, and losing natural predators means that, ironically, getting rid of aphids altogether could lead to a boom in their numbers, creating a more serious problem in future, as Master Horticulturist Colin Skelly shares:
“During my career, there has been a shift from viewing what were considered pests towards viewing them as part of the garden ecosystem.
“It does take some restraint to avoid wanting to remove ‘pests’ but they are part of the food chain.
“If you like the more charismatic wildlife in your garden, such as birds, then you need to build the food chain and expand the relationships in it rather than breaking the chains and reducing them.”
However, the reason that woolly aphids are considered a pest is that as they feed and create lumps and bumps on the bark, they leave these areas of the tree more vulnerable to more serious issues.
The lumps created in the bark by the chemicals that these insects excrete can split once the frosty weather of winter arrives, creating points of entry for disease.
These wounds can unfortunately allow in the fungal disease known as apple canker, which can create dead sunken areas and eventually kill off whole branches of a tree.
So, though the aphids themselves will not threaten the tree greatly, their actions can allow in diseases that pose far more of a threat.
Woolly Aphid Solutions
A serious infestation of woolly aphids is, of course, not desirable, because of the damage they do to the bark and the potential for disease to gain access through these points.
However, as mentioned above, this does not mean that we should aim to eradicate them entirely.
Keep Population In Check
Where we can, we should aim to accommodate pest species in our gardens and value them for their contribution to the ecosystem as a whole.
You can certainly have both apple trees and woolly aphids in your garden.
The key is, rather than trying to get rid of woolly aphids, to embrace them in smaller numbers and take steps to try to keep their population in check.
The main way in which you will do so in an organic garden is by encouraging healthy populations of the creatures that like to eat aphids and that prey on them to keep their numbers down.
Encourage Natural Predation
To control aphids in your space, creatures like ladybirds, lacewings and hoverfly larvae will act as natural predators as they love to feast on aphids.
Creating an environment for these creatures to thrive includes avoiding the use of pesticides and herbicides and planting to attract them.
Leaving wilder and less managed areas of space in your garden is always a great idea if you want as broad a range of different beneficial species as possible.
Creating guilds of beneficial companion plants around a fruit tree can aid the fruit tree in numerous ways and increase the yield that you are able to achieve.
One type of companion plant to include within a fruit tree guild are plants that help to bring in insects to the space to aid in pollination and pest control.
Research has also shown that earwigs can also help to reduce aphids on fruit trees, and they won’t do fruit trees like apple trees any harm.2Earwigs Management Guidelines. (n.d.). UCIPM. Retrieved March 9, 2023, from https://ipm.ucanr.edu/PMG/PESTNOTES/pn74102.html
You can increase the number of earwigs in your garden or orchard by providing a habitat for them.
Create brush piles and provide shelters like flower pots with hay stuffed loosely inside to do this.
Scrub Small Trees
If you spot an infestation on a small tree, it is possible to further control the population by simply scrubbing the areas where the colonies are seen using a brush with stiff bristles.
If you decide to take this step, it is best to do so in spring or early in the summer before the population booms.
Keep in mind that you should tolerate some aphids as part of the ecosystem in a healthy and organic garden, so don’t go too crazy with this method.
Why Not To Use Pesticides
Pesticide sprays, even organic ones, are unlikely to be effective on taller trees unless you can reach the entirety of the plant, and winter washes don’t control these aphids because they overwinter in fissures where the wash will not easily reach.
Remember, pesticides can also cause harm to beneficial wildlife, and synthetic pesticides are never, ever to be used in an organic garden.
Woolly aphids rarely become a major problem for apple trees, so as long as you control their population by boosting biodiversity and welcoming a range of wildlife where you live, you should be able to tolerate these insects and simply let them get on with their lives.
