Geum sawflies

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

Geum sawfly ( Claremontia waldheimii ) on Geum

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 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. 

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 infested plants

Control

Geums can cope with some damage and low numbers of larvae and light damage can be tolerated.

Non-pesticide control

Regularly inspect plants during the growing season and remove larvae from leaves.

Pesticide control

  • If numbers of larvae are too high for hand picking, control may be achieved by spraying with pesticides. Spaying at dusk is likely to give the best results
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug 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 Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug 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 pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners  (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

The larvae of geum sawflies (Claremontia waldheimii and Monophadnoides rubi) can cause extensive defoliation of cultivated and wild Geum species.

There is one generation a year with larvae active during late May and June. They initially they feed concealed between the folds of unexpanded leaves. The larvae of both species are pale green with rows of bifurcated 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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