Raspberry Cane Midge

Key Points

Raspberry Cane midge infestations can cause severe damage and lead to secondary fungal attack in raspberry crops
Lorsban WG should be applied once longitudinal splits are found on young canes
For best results, Lorsban WG must be applied to the bottom 60cm of young canes
Applications of Lorsban WG can control Raspberry Cane midge and many other fruit pests

Introduction

Cultivated raspberries grown in England and Scotland can be attacked by Raspberry Cane midge — Resseliella theobaldi — and, less frequently, loganberries can also be attacked. Infestation with Raspberry Cane midge causes damage in two ways: as a result of direct feeding by midge larvae and by secondary fungal infection of the wounds leading to midge blight. Heavy infections of midge blight can lead to death of affected fruiting canes.

First generation larvae produce deeply penetrating lesions that become cankered by August. Stem tissue is damaged allowing fungi to attack the vascular system before cork matures. Cankered canes are physically weak and liable to be broken, but they can survive and produce fruit in the following year.

Second and third generation larvae attack cork layers at a time when damage can not be repaired. Feeding damage at this time of the season allows secondary fungal attack to penetrate deep in to vascular tissue. Irregular brown lesions appear on the surface of the cane, often covering the complete circumference.

Biology

Overwintering occurs as the larval stage of the life cycle. The first adult emergence occurs in England during late April until early June, and approximately one month later in Scotland. Adult Raspberry Cane midges are small, reddish-brown in colour and only capable of weak flight.

Females lay many small, elongate, translucent eggs in rows under the flaps of splits or in wounds in the canes. Splits are usually found on the lowest 40cm of canes and these are preferred for egg laying. Infestations only reach damaging levels when the peak of adult emergence from the overwintered generation coincides with the development of splits.

Translucent larvae hatch from eggs after about 7 – 10 days and feed on the outer tissues of the cane. They soon change colour to orange or yellow and reach 3mm long when fully grown. Once mature, after approximately two to three weeks of feeding, larvae fall to the ground and burrow in to the soil to a depth of 1cm to 4cm. Here a cocoon is formed and pupation takes place.

Second generation adults emerge in late June in England and in July and August in Scotland. At this time susceptible raspberry varieties develop extensive splits as the cork matures and the rind peels. Many eggs are laid in these splits at the base of young canes and second generation larvae feed on newly exposed tissue. These larvae drop to the ground once fully grown, burrow in to the soil and form cocoons. In south and south-west England some larvae will produce a third generation of adults, but most will overwinter as larvae and emerge as adults the following spring.

Product Choice

Applications of Lorsban* WG (active ingredient chlorpyrifos) during early to mid-May in England and late May to early June in Scotland will control infestations of Raspberry Cane midge. Spray one week later in both areas after a cold spring.

First applications should be made when small longitudinal splits are found on young canes. Repeat 10 – 14 days later — just before, but not during, flowering. Direct spray into bottom 60cm of young canes. Do not apply to crops in flower or to those in which bees are actively foraging. Do not make applications when flowering weeds are present.