Geranium sawfly

The greyish green larvae of geranium sawfly larvae eat holes in geranium leaves during spring and summer.

Geranium sawfly larvae

Quick facts

Common name Geranium sawfly
Scientific name Ametastegia carpini
Plants affected Geranium
Main symptoms Holes in leaves
Most active May to September

What is geranium sawfly?

Sawflies are in the same group of insects as bees, ants and wasps (the Hymenoptera). They have caterpillar like larvae that feed on plants the adults are winged insects that can appear fly-like. 

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. 

Control

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 so this insect can be tolerated.

Check geranium frequently from May onwards so action can be taken before a damaging infestation 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 damage 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.

Non-pesticide control

  • Where possible tolerate populations of sawfly
  • 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
Pesticide control
  • If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spraying at dusk is likely to give the best results
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Neudorff Bug Free Bug and Larvae Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact 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)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
Follow label instructions when using pesticides. 

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.

Download

Pesticides for gardeners (pdf document outlining pesticides available to home gardeners)

Biology

There are two generations a year of geranium sawfly with larvae present in May and September. Fully grown larvae pupate in the soil, the September generation overwintering in this state. Adults emerge in spring and lay eggs on the foliage.

See also...

Big Garden Sawfly Survey (External link) 

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