Solomon's seal sawfly

This insect is a caterpillar-like larva of a sawfly that eats the leaves of Solomon’s seal plants.

Solomon's seal sawfly larvae feed in large groups so damage can occur very quickly. Keep vigilant for early signs;

• 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 damage caused by the sawfly larvae can appear severe it normally occurs after flowering and the plants will usually put on healthy growth in the year following an attack. Therefore this insect doe not necessary require controlling as the plants will survive.

Non chemical

Search for the larvae and remove them from the underside of leaves.

Chemical

• If infestations are too heavy for hand picking, control may be achieved by spraying with pesticides. Spaying at dusk is likely to give the best results
• Organic pesticides, such as those containing pyrethrum (e.g. Bug Clear Gun for Fruit and Veg, Defenders Bug Killer, ecofective Bug Killer) will control young larvae but larger larvae are more tolerant of these insecticides
• Synthetic pesticides containing deltamethrin (e.g. Sprayday Greenfly Killer, Provado Ultimate Bug Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), cypermethrin (e.g. Py Bug Killer) or the systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) may give some control of larger larvae
• 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)

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 but may produce reduced growth in the following year.

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