There are many different types of Aphids that can be found on trees and some so small that it is difficult to see them with the naked eye.
What we have seen in our nursery the last season is the green, brown & woolly aphid.
The woolly aphid generally appears as white fluff on the underside of the tree leaves and can sometimes be seen om the stem as well where trees have recently been pruned back.
The green or brown aphids are more difficult to spot, you will often see a collection of these aphids on soft new growth.
One or two aphids found on the tree is not a problem as the natural predators will control them.
The aphid population can explode rapidly, so the tree can be infested within a week.
If the tree however is struggling with an infestation the natural predators cannot keep the population under control.
Aphids are classified as sucking insects (Aphids, scale, spider mites & white fly), meaning that they suck nutrients out of the leaves and stems of the plant in order to survive and reproduce.
You will notice little yellow spots on the tree leaves when aphids are present and feeding on the tree.
New leaves will present as deformed as they develop and grow to full size.
Sucking insects (Aphids, scale, spider mites & white fly) excrete a clear sticky, sugary substance called Honeydew.
As aphids are very vulnerable insects they use the Honeydew to attract ants who collect the substance as food and in exchange protect the aphids against predators. Ladybugs are natural predators of aphids, so it’s always a good sign if you see a few ladybugs on your trees.
Unfortunately it is not possible for the ants to collect all of the honeydew available.
This then results in the tree leaves, branches & stems becoming sticky.
With the abundance of food available on the tree this gives opportunity for other organisms to utilise the food for survival.
One such an organism is a fungus commonly known as sooty mould.
Sooty mould appears as a black substance growing on the honeydew.
It looks unsightly in the landscape, but is not harmful to trees.
It is most commonly found in periods during the year where we are experiencing high temperatures and the tree is experiencing stress due to a lack of moisture.
The only way to control the outbreak of this fungus is to control to population of the aphids with the appropriate chemical treatment, thus reducing the amount of honeydew that is excreted.
Leaves of the tree can also be washed to dilute the sugar-syrup as well as to remove the black mould.
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