Emma Schaffert and Luke Hailey of Bartlett Tree Reseach discuss symptoms of and treatments for the cypress aphid
Browning of conifer hedging is not an uncommon sight in our towns and cities. There are many possible causes, for example it could be due to overpruning, lack of water, exposure to high winds, fungal diseases and even de-icing salts.
Conifer browning is also frequently caused by the pest known as the cypress aphid (Cinara cupressi). This brown or black insect is a sap-sucker, meaning it feeds by piercing the foliage of several cypress species with its straw-like mouthparts (stylet) and drinks their sap. This causes the foliage to gradually yellow and dry out in appearance. They’re most active in late spring and early summer, although the symptoms will usually be at their worst in late summer.
A wide range of aphid species have been a issue already this year and with a mild winter and favourable conditions, their populations are thriving.
This pest can be difficult to identify as it blends in well with the brown conifer stems. However you will often find a sticky build up of the sugary honeydew excreted by the aphid. This can then encourage a fungus known as sooty mould to move in. This powdery black coating of sooty mould doesn’t directly damage the plant itself other than by blocking out the light, but it is worth noting as it is a good indicator of sap-sucking insects being present.
Initially foliage becomes severely yellowed and browned. Subsequently affected needles fall in large numbers. Eventually crowns become thin consisting of a few bare needles. It is highly unlikely that a tree will die from a single attack by aphids alone; however, growth is likely to be reduced. Infestations year after year will have more serious consequences. Affected trees could require up to three years for complete recovery throughout the canopy once treated.
Transmission of viruses carried from diseased to healthy plants on the aphid’s stylets or in their saliva are also a possible issue, depending on the host. These can cause foliar symptoms such as leaf deformities and discolouration, with further impacts on plant health.
Non-chemical control is seldom effective, with the exception of releasing adult ladybird beetles and larvae which are voracious predators of aphids. Reducing the application of nitrogenous fertilisers so that young growth is less attractive to the aphids can theoretically help but rarely shows significant results.
Spray oil is applied with an appropriate insecticide when aphids are present and/or at the first signs of damage, killing the insect by direct contact. Bartlett Tree Experts has considerable experience treating this pest and using specially developed pest management strategies we are able to control current infestations and prevent future attack.
Emma Schaffert is a research technician for the Bartlett Tree Research and Diagnostic Laboratory.
Luke Hailey is a research technician and plant ecologist. He graduated from the University of Reading in 2012 with first class honours in biological sciences.