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Horse Chestnut Scale


Horse Chestnut Scale

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Caused By:-     The Scale insect Pulvinaria regalis


Horse Chestnut Scale(Pulvinaria regalis) is a sap feeding insect that feeds on several species of trees including Sycamore (Acer pseudoplatanus), Lime (Tilia), Magnolia(Magnolia species) and Horse Chestnut (Aesculus). It was first noticed in the UK in the 1960 and is now common throughout the country. Infestations are usually notable in the summer when the females deposit eggs under white cotton-wool-like waxy threads secreted from the edge of the scale which are deposited on the bark. The fully developed scales are dark brown, flattish, round and up to 5mm long. later the scale dies and drops off leaving the egg masses dotted over the bark, which is unsightly.Once summer arrives the eggs hatch and the young scales take on a pale yellow colour and feed on the undersides of the leaves. In Autumn they move onto the bark and over-winter as immature nymphs. The effect on the growth of the host trees by the feeding of nymphs is usually minimal, but can be severe especially as it can spread rapidly. One interesting fact about this pest is that it is rarely found in rural areas and is usually found on trees in cites where there is paving. This is probably because of the warmer micro-climate next to tarmac roads. Picture from Wikimedia Commons.
See these other Scale insects Azalea Bark, Azalea Cottony, Beech Bark, Brown, Eucalyptus Gumtree, Euonymus Mussel, Hemispherical, Hydrangea, Juniper, Mussel, Oleander, San Jose, Scale, Soft, Wisteria, Wooly Vine.


As most of the host trees are very large it is often tolerated, but if the tree can be given a winter insecticidal oil or tar wash This should help eliminate this pest. Spraying with an insecticide in early summer when the young nymphs are feeding on the leaves is also a possibility. As they are scales it is probably best to use a systemic insecticide.

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