Solomon's seal sawfly
The grey caterpillar like larval stage of Solomon’s seal sawfly can defoliate Polygonatum species and hybrids in early summer.
Latin name Phymatocera aterrima
Plants affected Solomon’s seal, Polygonatum species and hybrids
Main symptoms The foliage is eaten by pale grey caterpillar-like larvae
Caused by Larvae of a sawfly
What is Solomon's seal sawfly?
Sawflies are a group of insects in the suborder (Symphyta) of the Hymenoptera (bees, ants and wasps). There are about 500 species of
The larvae of Solomon's seal sawfly feed on the leaves of Polygonatum.
Solomon's seal sawfly larvae feed in groups and defoliation can occur very quickly. Defoliation usually occurs after flowering and plants normally recover and grow in the following year. Polygonatum is also often defoliated by slugs and snails, a night time search will often reveal the culprits.
- Greyish white caterpillar-like larvae with black heads and up to 2cm (¾in) long seen on the underside of the leaves, eating elongate strips out of the foliage
- Complete defoliation may occur
- Purplish brown scars, up to 2cm (¾in) long, may be seen on the leaf stems where eggs were inserted
Whilst the defoliation caused by Solomon's seal sawfly can appear severe it normally occurs after flowering and the plants will usually put on healthy growth in the following year. Therefore this insect can be tolerated and the plants will survive.
Check susceptible plants frequently from late 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, plants usually recover from defoliation
- Encourage predators and other natural enemies of sawfly in the garden, such as birds and ground beetles.
- Check plants regularly from May onwards 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)
Adult Solomon’s seal sawfly are black-bodied insects, 8-9mm long, with two pairs of blackish grey wings. In appearance they are similar to medium sized flies but are in the same group of insects as the bees, ants and wasps, the Hymenoptera. They emerge in late spring at about the time when their host plant is coming into flower.
The female uses her saw-like eggs-laying organ to insert rows of eggs into the leaf stems. This causes vertical purplish brown scars to develop where the eggs were inserted.
The larvae feed together in small groups on the underside of the leaves. Initially they make small elongate holes but as the larvae increase in size, their appetite also increases. By mid-summer, the stems may have been stripped of foliage.
The fully fed larvae go into the soil where they overwinter and pupate in the following spring. Defoliated plants will survive.
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