A light at the end of the polytunnel: new potential products for controlling blackberry leaf and raspberry cane midge

If not sufficiently controlled the blackberry leaf midge and raspberry cane midge can cause major damage in raspberry production. Female raspberry cane midge lay eggs in splits in the canes and the resulting larvae feed on the tissues underneath the bark. The tissue damage allows secondary pathogens to enter leading to cane blight and ultimately weakening and snapping of the cane. The blackberry leaf midge is a leaf-galling midge. Females lay eggs in newly-formed leaves. Larval feeding damages the leaves causing them to be creased, pleated, or curled, and damages the shoot tip. This halts the shoot from flowering, directly damaging fruit production. If you unroll the leaf-galls it is usually possible to see larvae inside the curls.

The midges have 2–3 generations per year. It is often reported that the first generation of raspberry cane midge emerges in May or June. However, in our trials in Kent this year our pheromone monitoring traps reached threshold on 13^th April – unlucky for some! The blackberry leaf midge reached threshold a week later. Control of the first generation is vital to stop an outbreak before it becomes overwhelming later in the season, so monitoring with pheromone traps is hugely important. If our dates are anything to go by, make sure the traps are out early and check them at least twice per week so you get that first spray spot on.

We ran trials to test four products (two synthetic insecticides and two bioinsecticides) alongside Decis Protech and an untreated control.

The results showed several of the products are highly effective against blackberry leaf midge. Deltamethrin (Decis Protech) is commonly used by growers and it performed well in controlling larvae and also reducing leaf damage. Two other products which are not yet registered for use in raspberry performed extremely well. If registered they may provide much needed options for controlling these pests. FLiPPER showed promise and it would be worth investigating its suitability further.

We hope to repeat our trials with raspberry cane midge next year. Future work should focus on developing an optimal spray programme for both pests and pesticide resistance management.

And don’t forget to monitor those midges!