Geum sawflies

The caterpillar like larval stage of two species of sawfly can feed on Geum in spring and summer.

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Geum sawfly (Claremontia waldheimii) on Geum

Quick facts

Common name Geum sawflies
Latin names Claremontia waldheimii and Monophadnoides rubi
Plants affected Geum species
Main symptoms The foliage is eaten by pale green caterpillar-like larvae
Caused by Larvae of sawflies
Timing May-July

What are Geum sawflies?

Sawflies are a group of insects suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of sawfly in Britain. They have caterpillar like larvae that feed on plant material and are named after the saw like egg laying organ used by females to lay eggs in plant material. Adults can come in a range of colours many are black, green orange or striped yellow and black. Most are small (< 1cm) but some species such as the Birch sawfly (Cimbex femoratus) can be over 2 cm long. Several species can be found in gardens and are part of the biodiversity a healthy garden will support. More information can be found at The Sawflies of Britain and Ireland webpages

There are two species of geum sawflies they have pale green larva, with small white spines. The larvae reach 15 mm in length that eat the leaves of Geum plants in the spring and summer. The adult insects are about 6 mm long and mainly black.

Symptoms

Geum sawfly larvae initially feed concealed between the folds of unexpanded leaves. As they grow they cause large irregular holes and damage can occur very quickly and defoliation can be extensive. Keep vigilant for early signs;

  • Pale green caterpillar-like larvae with small whitish spikes up to 15 mm long
  • Leaves can be reduced to a network of the larger leaf veins, affecting the appearance and vigour of  plants
  • Affected plant often recover with no long term effects

Control

Geums can cope with low numbers of larvae and damage can usually be tolerated and the presence of these insects treated as part of the biodiversity a healthy garden supports.

Check geums frequently from spring 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 treat this sawfly as part of the biodiversity a healthy garden can support, plants often recover from defoliation
  • Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
  • Check plants regularly in May and June for the presence of larvae and remove by hand where practical
Pesticide control

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 give the best results
  • Organic contact insecticides containing natural pyrethrinrum (e.g. Bug Clear Gun for Fruit & Veg, 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
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

The larvae of geum sawflies (Claremontia waldheimii and Monophadnoides rubi) feed on the foliage of cultivated and wild Geum species.

There is one generation a year with larvae active during late May and June. They initially feed concealed between the folds of unexpanded leaves. The larvae of both species are pale green with rows of bifurcated (divided into two) whitish spines on the dorsal surface. When fully fed in late June they go into the soil where they spin silk cocoons, where they overwinter. The adults are 5-6mm in length, black in colour and emerge between late April and early June.

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