Large rose sawfly

The caterpillar like larvae of large rose sawflies eat the leaves of wild and cultivated roses.

Larvae of large rose sawfly. Image: RHS, Horticultural Science

Quick facts

Common name: Large rose sawfly
Scientific name: Arge pagana and Arge ochropus
Plants affected: Wild and cultivated roses
Main symptoms: Split shoots and defoliation
Most active: Late May to October

What is large rose 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. 

Large rose sawflies have pale spotted black, green and yellow larvae that eat the leaves of roses, sometimes causing severe defoliation. The adults have yellow abdomens with mainly black thorax and heads.

Roses can also be attacked by other sawflies such as the rose leaf-rolling sawfly and rose slug sawfly or slugworm.

Symptoms

You may see the following symptoms:

  • The female sawflies lay eggs in soft young rose stems, they can sometimes be found with their rear ends inserted in the stems. The stems often split open where the eggs were laid, resulting in elongate scars
  • Whitish green, caterpillar-like larvae with black spots and yellow blotches cause extensive defoliation in early and late summer

Control

Healthy roses can cope with some defoliation and the presence of some larvae can be tolerated.

Check roses 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 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 egg laying females, egg scars and larvae. Eggs within the scars can be destroyed by running a fingernail (or equivalent) down the scar. Larvae can be removed 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

In Britain there are two species of large rose sawfly: Arge pagana and A. ochropus. The adult insects of both species have yellow abdomens with the legs, thorax and heads being mostly black. Arge pagana is the more common species. 

Rows of eggs are inserted into soft young rose shoots and female sawflies are sometimes seen dangling from such stems, attached only by their saw-like egg-laying organs.

After hatching, the larvae feed together in family groups. They are pale green with black spots and yellow blotches, and are up to 25mm (about 1in) long. When fully fed, they go into the soil to pupate.

The large rose sawfly (Arge pagana) will produce two (sometimes three) generations from May to October. Arge ochropus usually has a single generation in early summer, but sometimes there is a second generation in late summer.

See also...

Big Garden Sawfly Survey (External link) 


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