A caterpillar in the core of an apple, a ribbon-like scar on its skin or gooseberry bushes stripped to the veins can be alarming, but the Royal Horticultural Society (RHS) generally advises gardeners to put such damage in proportion. This guide summarises the RHS advice pages for codling moth, apple sawfly and gooseberry sawfly. The advice is written for home gardens in the United Kingdom and concerns fruit grown at home. It is general information and not a treatment recommendation.
Codling moth in apples and pears
According to the RHS, codling moth caterpillars bore into the fruit of apple and pear trees in mid to late summer, and are most active from June to September. Quinces and walnuts are affected less often. Signs are a small exit hole in the side of ripe fruit or at the eye end, tunnelling and frass in the core, and a small white caterpillar with a brown head. Damaged fruit tends to ripen and drop early.
The RHS advises tolerating some fruit loss where possible, because often only a small proportion of fruit is affected, and encouraging natural enemies such as birds, wasps and ground beetles. It adds that it is not worthwhile controlling codling moth on quince or walnut, as the damage is rarely significant. Adults emerge in late May to June, eggs are laid on or near developing fruit from June to mid-July, and the caterpillar feeds in the core for about four weeks before leaving the fruit to overwinter in leaf litter or under loose bark.
Pheromone traps and nematodes
The RHS describes pheromone traps hung in the tree in early May, using a synthetic version of the female moth’s chemical to attract males onto a sticky sheet. It says these traps alone rarely control codling moth but monitor moth activity, helping to time other action so that it is targeted. On isolated trees they may catch enough males to reduce mating success. Adding bird netting reduces the risk of birds entering the trap.
A mixture of pathogenic nematodes sold as ‘Fruit and Vegetable Protection’ may give some control. The RHS says it is sprayed on the trunk, branches and the soil under the branches in September to October, after the caterpillars have left the fruit. It gives no protection in the following year against female moths flying in from nearby gardens, and may not be worthwhile where apples and pears are widely grown. The RHS also warns that nematode controls could infect non-target animals within the same group and should be used with care, only for a specific problem.
Apple sawfly
Apple sawfly larvae are caterpillar-like and feed beneath the skin of developing apples before burrowing into the fruit. The RHS gives late April to June as the timing. In late May and June affected fruitlets have holes with blackish-brown pellets spilling out, and each larva can feed on several fruitlets, often damaging three to five. Most affected fruitlets drop in the June drop. Fruitlets that suffered only early feeding can stay on the tree, developing a misshapen shape and a ribbon-like scar about 4mm wide, but they are usually still edible.
The RHS says the presence of apple sawfly can usually be tolerated, and in years of heavy fruit set a little fruit thinning caused by the sawfly can be beneficial. Cultivars such as ‘Worcester Pearmain’, ‘Charles Ross’, ‘James Grieve’ and ‘Ellison’s Orange’ seem particularly susceptible, while cooking apples are rarely affected apart from ‘Early Victoria’ and ‘Edward VII’. Gardeners should check apples once fruit begins to set, and can pick off damaged fruitlets to stop larvae moving to other fruitlets or into the soil.
Gooseberry sawfly
The RHS says three species of sawfly feed on the leaves of gooseberries, red currants and white currants, with the larvae being green with black dots and the main activity from April to September. The small gooseberry sawfly can have up to four generations from late April, while the pale spotted species has one generation a year with larvae in May and June.
The RHS notes that plants will usually survive complete defoliation, although it may reduce the yield. Its advice is to tolerate sawflies where possible as part of garden biodiversity, check plants regularly from April for larvae so that a damaging population does not develop, remove them by hand if required and where practical, and encourage natural enemies such as birds, wasps and ground beetles.
Putting it in proportion
The RHS pages share a theme: keep watch early, tolerate light damage, favour natural enemies, and use traps or nematodes only where they are justified. The site’s guide to buying predators and nematodes covers timing and handling in more detail.
FAQs
Can I still eat apples with an apple sawfly scar?
The RHS says fruits that suffered only early feeding develop a ribbon-like scar but are usually still edible.
Do pheromone traps control codling moth?
The RHS says the traps alone rarely control codling moth but monitor activity, and can help time other action.
Will gooseberry sawfly kill a bush?
The RHS says plants will usually survive complete defoliation, although the yield may be reduced.
The bottom line
For fruit grown at home, the RHS treats codling moth, apple sawfly and gooseberry sawfly as pests to monitor and tolerate in moderation rather than to eradicate. Pheromone traps in May help time any action against codling moth, damaged apple fruitlets can be picked off, and gooseberry larvae can be removed by hand. Nematodes are described with caution, because they can affect non-target animals. This is general information, not a treatment recommendation.
Sources
- Codling moth (rhs.org.uk)
- Apple sawfly (rhs.org.uk)
- Gooseberry sawfly (rhs.org.uk)