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Soft scale is a very widespread and common scale insect attacking a wide variety of garden and glasshouse plants. It is a flat, oval pale yellow/brown insect usually found near the midribs of leaves and on stems and produces large amounts of honeydew.
Soft scale on the underside of a bay leaf
There are many types of scale insects encountered by gardeners, they are sap sucking true bugs. Soft scale is a flat, oval, pale yellow/brown insect. The pale covering of the insect is waxy and repels liquids. The adults reach up to 4mm long, the immature (nymph) stages are much smaller. It is found near the midribs of leaves and on stems.
It produces large amounts of honeydew and breeds throughout the year. It attacks garden and glasshouse plants, including bay, Ficus and Citrus species, ivy, ferns and many others.
Heavy infestations of soft scale are characterised by heavy deposits of sticky honeydew upon which a black non-parasitic fungus sooty mould often grows. The 4mm long pale yellow brown insects will be evident upon examination of the undersides of leaves and stems.
Soft scale is difficult to eradicate. Whilst scraping the insects off the leaves can help reduce infestations this is unlikely to give good control. It can be worth considering replacing heavily infested plants.
Soft scale can be difficult to control with sprays as the waxy covering gives them some protection and the best results are achieved by spraying against the newly hatched crawlers. Heavily infested plants may need several applications. Scales often remain attached to the plant long after they have died, but new growth will remain free of scales and honeydew if the treatment has been successful.
Note: Only lambda-cyhalothrin and deltamethrin can be used on bay leaves used for culinary purposes and there are no synthetic pesticides available for use on citrus although organic types can be used. One application/year of deltamethrin is permitted on culinary herbs; two for lambda-cyhalothrin and there is a 7-day interval between treatment and using the foliage.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Biological control suppliers (Adobe Acrobat pdf)
Female soft scales can lay up to 200 eggs underneath their body. These hatch into small pink crawler nymphs which move over the plant surface before settling down to feed. They are small enough to be easily blown around in wind currents and this is the main way that plants are colonised. The nymphs suck sap from the leaves and stems and, once feeding has commenced, they usually remain immobile for the remainder of their lives.
In warm conditions breeding is continuous throughout the year.
A waxy layer is secreted over their bodies to form the scale, and this layer gives them some protection from pesticides.
Chemical labels explained
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