The greyish green larvae of geranium sawfly feed on geranium leaves during spring and summer.
Scientific name Ametastegia carpini
Plants affected Geranium
Main symptoms Holes in leaves
Most active May to September
What is geranium sawfly?
Sawflies are a group of insects suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of
Geranium sawfly has greyish-green larvae that reach 12mm in length. The larvae feed on leaves of hardy geranium in May and September leaving a holed appearance. The larvae readily drop of the plants when disturbed and so are not often seen. The adult sawfly is a black 10mm long fly-like insect.
Although the damage on the foliage can be considered unsightly, it is generally not extensive enough to affect the plant’s growth or its ability to produce flowers and this insect can be treated as part of the biodiversity a healthy garden supports.
Check geranium frequently from May onwards so action can be taken before a damaging population has developed. When choosing management options you can minimise harm to non-target animals by starting with the methods in the non-pesticide control section and avoiding pesticides. Within pesticides the shorter persistence products (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. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
- Where possible tolerate populations of sawfly, this species rarely causes sever defoliation and is part of the biodiversity a healthy garden can support
- Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
- Check plants regularly from May for the presence of larvae and remove by hand where practical
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.
- If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to be more effective
- Organic contact insecticides containing natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer). Several applications of this short persistence products may be necessary to give good control
- 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
Plants in flower should not be sprayed due to the danger to bees and other pollinating insects.
Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.
Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)
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