Help us achieve our goals:
make a donation »
Join the RHS today and
support our charity
Free personalised gardening advice
RHS members get reduced ticket prices
RHS members get free access to RHS Gardens
Reduced prices on RHS Garden courses and workshops
020 3176 5800
Mon – Fri | 9am – 5pm
Make a donation
Join the RHS today and support our charity
I have forgotten my password
Keep me signed in
Register for free to receive our newsletters, add comments to blogs/articles and to save content.
There are two species of moths with caterpillars that can cause extensive defoliation of Cotoneaster horizontalis. The moths have some additional host plants, including hawthorn but other Cotoneasters are unaffected. The affected parts of the plant are covered in silk webbing produced by the caterpillars.
Cotoneaster webber caterpillars are the larval stages of two moths: the hawthorn webber and porphyry knothorn.
Affected plants will show the following symptoms:
Whilst the appearance of this pest can be alarming and almost all of the foliage can become covered in webbing and turn brown, the plants usually recover without treatment and so control is not always necessary.
Inspect plants for signs of webbing and damage in late spring and late summer. If the infestation is confined to a few shoots, these can be pruned out.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners).
The life cycles of hawthorn webber and porphyry knothorn moth are broadly similar, with one generation a year:
Hawthorn webber moth caterpillars are 12-15mm long when fully grown and they produce extensive white silk webbing that covers their feeding area. Caterpillars of porphyry knothorn moth are a little larger and stouter than those of the hawthorn webber. They spin greyish-white silk tubes, which incorporate fragments of plant material, along the stems, so the webbing is less obvious that that produced by hawthorn webber caterpillars.
Angle shades mothBox tree mothCodling mothEncouraging moths into your gardenHolm oak leaf-mining mothsHorse chestnut leaf-mining mothLeek mothOak processionary moth Pea mothPlum mothProtect your gardenPyracantha leaf mining mothRHS statement on pesticides in horticulture Winter moth caterpillarsWoolly aphid
the RHS today and get 12 months for the price of 9
RHS members can get exclusive individual advice from the RHS Gardening Advice team.
Register for the site or sign in to share your experiences on this topic and seek advice from our community of gardeners.
We're a UK charity established to share the best in gardening. We want to enrich everyone's life through plants, and make the UK a greener and more beautiful place.
Join the RHS today and get 12 months for the price of 9