Apple tree branches covered in patches of white, woolly fuzz? What you’re seeing is a woolly aphid infestation. These pests can be controlled by spraying a few applications of horticultural oil spray (preferably a natural oil-based product rather than a petroleum oil based one) 7 days apart, it suffocates them quite effectively, and gets past the fluffy coat which repels liquids and protects them from most insecticides.
Problem solved? Maybe not…
The Root Cause of the Problem or Just a Symptom?
Too often in gardening we see the bad practice of quickly identifying a pest or disease and then jumping straight to a chemical control without looking any further.
Yes, we can spray this pest with that natural or synthetic product, but will it work? What if it doesn’t? Do we just spray more, or spray something else?
Too often in the agriculture and horticulture world, lip service is payed to the whole science of ecology, but it’s an inconvenient truth that’s more often ignored, as it’s much easier to pretend that plants ‘grow in a vacuum’ and don’t interact with their living and non-living surroundings. Sometimes the answers we seek lie outside the area we only choose to see.
Woolly aphid infestation on apple tree branches
One pattern often observed is that apple trees affected by woolly aphid also show of various yellow, brown or black blotches or spots on the leaves, which are caused by fungal diseases. Note, these diseases are different to the sooty mould formed from the honeydew excreted by the aphids. If we’re seeing this pattern, the logical question to ask is what would be causing the fungal diseases?
A common cause of fungal diseases is lack of air circulation, which causes wet leaves to stay moist, promoting fungal infections. This often happens when trees get too dense from lack of pruning, and the solution is to prune to open up the canopy to allow air and light through.
Sometimes apple trees may be planted hard up against a wall or fence, in a corner, or jammed between other trees, which can cause similar problems. Clearing space around trees, pruning and then spraying with the appropriate fungicide helps. Spraying with lime sulphur or copper fungicide during dormancy, potassium bicarbonate or an appropriate copper fungicide when trees are in leaf, is usually effective for many fungal diseases.
But what happens if the pests and diseases keep returning?
In the garden nursery where I work part-time, I started noticing gardeners reporting increasing incidences of woolly aphid infestations combined with leaf fungal diseases, which caught my attention. By chance, two of the apple trees I maintained at work had a similar problem. They did not fruit much, were constantly affected by woolly scale and leaf fungal diseases, yet they were planted in a location which was wide open, even severely windswept, with lots of open space around them. Yet no matter how many times I sprayed these two trees, the problems returned. Companion planting and beneficial predator insects released on site didn’t help much either. So, what could the problem be?
In Permaculture, we emphasise choosing the right plant for the right location, matching plants with their ecological niches, giving them the conditions they favour. To determine what we can plant where, we first ‘read the site’ to see where the ‘wild energies’ of wind, water and sunlight move through our location.
Applying these permaculture concepts, it was easy to read the site and identify the cause of the problem, the location where the apple trees at work were planted was in shade until around 1pm or 2pm, depending on the time of year, then received full west sun till sunset. Some fruit trees cope with varying degrees of shade, and just fruit less, but it appears that apples get very unhappy in shady locations, they get weak and sick!
Discussing the matter with customers who reported these same problems, I asked how much shade their apple trees were in – and surprise, surprise, their trees were shaded out significantly! The problem of shading and limited sunlight in backyard gardens is becoming more prevalent in the suburbs here in the major cities in Australia. Developers are buying up any available property, demolishing it, and putting up multi-storey high-density housing, built right up against the fence line, casting shade across neighbouring properties. To maintain privacy, neighbours are forced to plant tall screening trees, hedges and plants. The net result is that backyards in the suburbs are getting smaller and shadier, and apple trees are suffering from a lack of light.
Holistic Problem Solving – Seeing the Big Picture
If your apple trees are constantly being attacked by pests such as woolly scale and fungal diseases, and fruiting very little or not at all, and they’re being properly fertilised and watered, then the issue may be that they’re not getting enough sunlight.
Oh, they get enough sun – is a comment I hear often. I’m not buying your word for it unless you have recorded the approximate times when sun or shade passes over the apple tree at various times of the year when it’s in leaf! Fruit trees need a minimum of 6-8 hours of full sunlight all year round while they have leaves. The actual observation results may surprise you. Unless it an observation, it’s a guess, and if you wouldn’t risk your own life on a wild random guess, why would you do that with the lives of your trees?
No amount of spraying of any garden product, natural or chemical, is going to help keep a plant alive in the long term if it’s planted in the wrong location. If conditions have changed, and less light is available, assuming an apple tree is not too large in size, a viable option is to dig up the apple tree in winter when it’s dormant, and transplant it, moving it to a better location.
The reality is that garden problems can have multiple causes, and pests and diseases aren’t necessarily the actual cause of the problem, but often just the symptoms indicating a weakened and unhealthy plant or tree. Pests and pathogens serve a very important ecological role, to attack and eliminate unhealthy plants and trees in order to make space for healthy ones to replace them.
So before reaching for the garden sprays, it’s best to spend a bit longer looking at what could be affecting the health of your trees and plants and then take appropriate action. It will be less work for you in the long term and such an approach will ensure the long-term survival of the plants and trees in your garden!
More articles on Garden Pests, Diseases and Problems
Goodness! Again, thank you for saying so! This is a concept that is not easy to get through to people. My colleague in Southern California has serious problems with scale and aphid (although not woolly apple aphid) because the garden is so terribly crowded! Even without the insects, many plants are just too shaded!
Great article. Unfortunately my apple tree is riddled with these pests. But is in the centre or our garden in a large open space and gets sunlight all day. Could it get too much sun? Or do some spots just not work and we should give up and remove the tree?
Auckland is quite humid so maybe just not that good for apple trees.
Could the tree be too congested? These pathogens proliferate within congested trees. Pruning increases air circulation to sort of discourage the pests. Also, foliar debris that falls from the trees in autumn should be removed from the ground, as well as where it hangs up in the tree
If the air has good air circulation around it, and is pruned so the canopy isn’t too dense and light can pass through it, then you probably need to check the soil. Unhealthy soil doesn’t support healthy plants! Is the soil waterlogged or dry? Is there ample organic matter in the soil? Is the tree fertilised twice a year? Is the soil mulched? Is the soil structure good and friable (loose) or is it compacted? Lots of other considerations.