Leafrollers
Tortricidae — Choristoneura and Argyrotaenia spp.
also called Obliquebanded leafroller, Redbanded leafroller
A leaf folded and stitched shut with silk, with a green caterpillar inside that wriggles backwards violently when you open it. Mostly cosmetic on a mature tree.
The rolled leaf is the identification: folded over on itself or tied to a neighbor with fine silk, with frass and a green caterpillar 15–20 mm long inside. Touch the caterpillar and it thrashes backwards out of the roll and drops on a silk thread — a reaction so distinctive it is diagnostic.
- Leaves rolled, folded or webbed together at the shoot tips, tied with silk.
- The inside of the roll grazed to a papery window, with frass packed in.
- Fruit scarred where a leaf was tied against it and the caterpillar fed on the skin beneath.
- Blossom clusters webbed together and failing to set.
- A green caterpillar wriggling out backwards and abseiling away when a roll is opened.
Most species overwinter as small caterpillars under bark scales and start feeding as the buds break, which is when they do the most damage. Two generations a year in most of the range; the summer generation feeds on the leaves and fruit skin. Adults are small bell-shaped brown or gray moths.
Orchards and soft fruit, worst on trees that are dense and unpruned. Damage is heaviest in spring, on the blossom and the emerging leaves.
- Squash the rolls between finger and thumb as you find them — quick, satisfying and completely effective at garden scale.
- Spray Bt at bud break, while the caterpillars are exposed and before they roll a leaf around themselves.
- Prune to open the canopy so birds can reach the shoot tips.
- Hang pheromone traps to time the flight if you are treating a larger planting.
- Do nothing on a mature tree carrying a light infestation; the loss is trivial.
- Prune annually and keep the tree open, which reduces the sheltered shoot tips they want.
- Scrape loose bark from old fruit trees in winter, where the small caterpillars shelter.
- Keep the ground under the trees clear of leaf litter.
- Encourage the parasitic wasps and birds; leafrollers are heavily parasitized when not sprayed.
- Grease-band trunks and clear water shoots, which give the young caterpillars their route up.
- BatsChiroptera A single bat takes hundreds of moths and mosquitoes in a night, and the moths are the parents of your cutworms, corn earworms and hornworms. Put up a bat box on a warm south wall, leave a night-scented corner unlit, and never spray after dark. Grow to recruit it: Evening Primrose,Honeysuckle,Nicotiana,Summer Jasmine
- 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
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