Sawfly
Symphyta
also called Gooseberry sawfly, Rose slugworm, Solomon’s seal sawfly
Caterpillar-like larvae (gooseberry, rose, berberis kinds) that can strip a bush in days. Inspect leaf undersides from late spring and pick larvae off by hand.
Larvae that look like caterpillars but carry more than five pairs of fleshy prolegs — the reliable tell, and the reason Bt does not work on them. Green with black spots on gooseberries, slug-like and slimy on roses and pears, gray and gregarious on Solomon’s seal, and they rear up in unison when the leaf is tapped.
- A gooseberry or currant bush stripped to bare stems in under a week, usually starting in the center.
- Larvae lined up along the leaf undersides, feeding shoulder to shoulder.
- Rose leaves grazed to a transparent skeleton on one surface, then browning off.
- Solomon’s seal leaves reduced to shredded ribbons in early summer.
- Repeat attacks through the season as successive generations hatch.
Females saw slits into leaf tissue and lay eggs inside; larvae feed for two to three weeks then drop into the soil to pupate in a cocoon. Two or three generations a year on gooseberries — which is why a bush cleared in May is stripped again in July — and the final generation overwinters as a cocoon in the soil beneath the plant.
Warm late springs and early summers, and bushes with congested centers where the first larvae feed unseen. Damage is fastest on soft-leaved gooseberries and currants.
- Inspect the center of gooseberry and currant bushes from mid-spring — the first generation always starts low and inside.
- Pick the larvae off by hand; on a garden bush this is quick and completely effective if done early.
- Shake branches over an upturned umbrella or a sheet and collect what falls.
- Do not reach for Bt: sawflies are not caterpillars and it will do nothing.
- A stripped bush usually releafs and survives — water, mulch, and do not write it off.
- Prune fruit bushes to an open goblet so the center is easy to see into.
- Lightly fork or mulch under gooseberries and currants in winter to disturb the cocoons.
- Encourage birds, which take sawfly larvae readily once they find a colony.
- Check again three weeks after clearing the first generation — a second is coming.
- Grow umbel flowers nearby for the parasitic wasps and tachinid flies that attack them.
Gooseberries, redcurrants and whitecurrants above all; also roses, Solomon’s seal, berberis, pears, plums and aquilegia.
- Parasitic waspsBraconidae & Trichogramma Tiny, stingless wasps that lay eggs in or on caterpillars, aphids, and moth eggs — the white cocoons riding a hornworm are their calling card, so leave that caterpillar be. Umbel flowers with shallow nectar keep the adults fuelled. Grow to recruit it: Cilantro,Dill,Fennel,Lovage,Parsley,Sweet alyssum
- Spined soldier bugPodisus maculiventris A predatory stink bug — same shield outline as the pest, but with a sharp spine at each shoulder and a beak it uses to spear caterpillars and beetle grubs. Learn the spines before you squash a shield bug, because this one is on your side. Grow to recruit it: Dill,Fennel,Sweet alyssum,Yarrow
- Tachinid flyTachinidae Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies. Grow to recruit it: Cilantro,Dill,Feverfew,Parsley,Sweet alyssum
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