Cotton stringy scale
Cotton stringy scale is a recent arrival to Britain from the east Asia, being confirmed for the first time in 2018 from West Berkshire. It produces characteristic long stringy white egg masses and feeds on a wide range of woody plants but with little noticeable damage. Suspect cases should be reported to the relevant plant health authority.
Scientific name Takahashia japonica
Plants affected Many woody hosts, including Acer, Cornus, Magnolia and Morus.
Main symptoms Long, white string-like loops of eggs hanging from branches of trees
Most active Egg sacs appear in the summer, but may stay attached all year
What is cotton stringy scale?
Scale insects are sap 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.
Cotton stringy scale is native to the east Asia and was first recorded in Northern Italy in May 2017. It can feed on a wide range of woody hosts. The first case in Britain was reported in December 2018 from a Magnolia in West Berkshire, that had likely been imported from Italy. It is not recorded as damaging to plants in its native range or Italy, however, the long stringy egg sacs are very distinctive.
As a non-native, suspect cases should be reported to the relevant plant health authority.
- Cotton stringy scale produces long, string-like structures that loop around and are attached at either end to the branches of the tree. These structures, called ovisacs, hold the eggs of the insect. They are up to 5cm long, and made of a tough waxy substance and may remain attached to plants long after the eggs have hatched. The eggs hatch in late spring or early summer
- No other insect in Britain produces similar egg masses
- The adult scale insects are dark brown and oblong, approximately 7mm long and 4mm wide
Non-pesticide controlCheck susceptible plants frequently from spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section. If this is not sufficient to reduce the insects to acceptable levels then you may choose to use pesticides. Within this group the shorter persistence pesticides (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife than those with longer persistence and/or systemic action.
Cotton stringy scale does not usually affect the vigour of its host plants and so it presence can be tolerated.
- Where possible tolerate populations of this scale insect
- Adult scales and egg masses can be removed when seen but this may not reduce large populations
- Encourage predators in the garden, some ladybirds, parasitoid wasps and some birds will eat scale insects
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
Pesticide control is not usually necessary as this insect does not usually affect the vigour of host plants.
- For scales on deciduous plants including edible fruits, a plant oil winter wash (considered organic e.g. Growing Success Winter Tree Wash) can be used. This can control the overwintering scale nymphs in December-January when the plants are fully dormant
- The best time for summer spraying is in late spring or early summer when the more vulnerable newly hatched scale nymphs are present
- Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit and Veg) can give good control of scale insect nymphs. These pesticides have a very short persistence and so may require reapplication to keep scale numbers in check. Plant oil products are less likely to affect larger insects such as ladybird adults
- Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action (e.g. Ecofective Bug Control, RHS Bug and Mildew Control and SB Plant Invigorator). These are not considered organic
- More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer)
- A systemic containing the active ingredient Flupyradifurone (Provanto Smart Bug Killer) is available for use on ornamentals and selected edibles
- The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
DownloadPesticides for gardeners (pdf document)
- In Italy, there is one generation per year
- Eggs hatch in June, and the nymphs can be dispersed locally on the wind
- The nymphs and young adults are small and unlikely to be spotted until the adults mature and produce egg sacs in the summer months
- Many different woody hosts have been recorded, including those commonly grown in Britain including Acer, Albizia, Alnus, Citrus, Cornus, Cydonia, Juglans, Magnolia, Morus, Parthenocissus, Prunus, Pyrus, Robinia and Salix
- It is possible the known host range of cotton stringy scale will expand as it encounters new plants in Europe
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