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Yew Scale Damage

Posted by Lauren Barker- Horticulture Specialist on 09 August 2019 in Trees, Plants & Ornamentals
Yew Scale Damage

In recent weeks we have noticed an increase in calls regarding yew scale damage. Whilst this pest can be seen all year round, the damage they inflict is most prominent during the summer.

What are they?

Yew scale is a sap sucking pest that lives on the stems and leaves of a yew (Taxus).  This insect is most active during summer as this is when the adults are feeding, and the eggs are hatching. The reason yew scale can be seen all year round is mainly due to the presence of dead scales attached to the plant. Very similar in appearance to brown scale (a scale insect that feeds on a wide range of plants), yew scale is categorically different as it feeds on the yew tree- a tree that brown scale avoids.

What are the symptoms?

As yew scale are a sap sucking pest, they will cause infested trees to have yellowing leaves and lack vigour. Defoliation can also occur in cases of heavy yew scale infestation. You may also observe a black sooty mould on the excreted honeydew left by yew scale as they feed on the leaves and stems. Yew scale insects are identified as convex, oval, dark brown shells approximately 3-6mm long.

Specialist Control

Hallmark Zeon- a fast acting contact insecticide which can be used in forestry, agricultural crops (including winter and spring wheat, potato and sugar beet) and ornamental plants; it also has an EAMU (Extension of Authorisation for Minor Use) on various fruit crops- please speak to our team for a full list.

Decis Forte- a broad spectrum pyrethroid insecticide formulated to control pests such as aphids and caterpillars in a range of agricultural and horticultural crops. Decis Forte is an emulsifiable concentrate containing 100g/L deltamethrin. 

Both of these products are synthetic pyrethroid insecticides meaning they will work on a range of aphids, caterpillars, whitefly and other sap sucking pests so are not just limited to scale insect.

Unfortunately, the hard shells of the insects will remain even though the pest itself has been killed. All new growth should be clear of yew scale, however if you are concerned about the appearance of the scale shells on the plant SB Plant Invigorator can be used. SB Plant Invigorator will also help to wash off any sooty mould that has grown on the plant as a result of yew scale infestation.

If you have any questions about yew scale or any other pest, please give me a call.