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Scale insects are sap

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding. sucking true bugs belonging to several families in the Hemiptera. Typically the adults are immobile having a flattened or raised appearance, with no visible legs. They often look like a ‘scale’ on a leaf or stem, many species produce a white wax often covering egg masses. There are more than 100 species found in Britain, 26 of which have been introduced. More than 25 species can be found in gardens or on houseplants.

Yew scale is a sap-sucking insect that lives mainly on the leaves and stems of yew (Taxus). It is similar in appearance to brown scale however, brown scale is found on a wide range of plants but notTaxus. Yew scale has one generation a year and in early summer the adult insects can be seen on the leaves and stems. The eggs hatch in late June and July and the young scale nymphs then disperse and feed during the summer by sucking sap from the leaves. It is not unusual to find light populations of this scale on healthy yew plants.

• Convex, oval, dark brown ‘shells’, 3-6 mm long, occur on the woody stems
• It is not unusual to find this scale on yew, only heavy populations may affect vigour and cause defoliation
• A black sooty mould often develops on the sugary honeydew, that is excreted by the insects as they feed on sap
  Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding. and deposited on leaves and stems

• Light populations of yew scale are of little consequence on yew trees, indeed they are normal for a healthy yew and can usually be tolerated; well-tended, smaller, healthy plants are able to tolerate light populations of these insects
• Encourage predators in the garden; yew scale is a food source for some ladybirds , and other predators. Natural enemies will often keep populations of this insect in check