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.
How to know it
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.
What you'll see
- 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.
Where it comes from
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.
Dealing with it
- 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.
Keeping it out
- 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.
What it goes for
Apple, pear, cherry, blueberry, raspberry, strawberry and roses, along with many ornamentals.
Who hunts it for you
- 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
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com