Raspberry beetle

What you are looking at

You pick a raspberry and the stalk end has a dry brown patch, hard and shrunken, where the rest of the berry is soft and red. Tip the fruit into a bowl and a pale cream grub a few millimetres long, with a darker head and brown plates along its back, works its way out of the hollow.

On the plant the damage shows as fruit that will not come away cleanly. A sound raspberry slides off its plug; one that has been fed on at that point tears.

Blackberries and loganberries get the same beetle and show it as a shrivelled, hardened section of the fruit while the drupelets around it ripen normally.

Where it comes from

The adult is a small oval beetle about 4 mm long, greyish-brown and covered in fine hairs. It emerges from the soil in late April and May, feeds first on the flowers of nearby trees and shrubs, and then moves onto raspberry and blackberry flowers as they open.

Inside the open flower it feeds on the anthers and lays eggs. The larva hatches onto the developing fruit and feeds at the plug end, which is why the damage is always at the top of the berry and never in the middle.

When the fruit ripens or falls, the larva drops to the ground, burrows into the top few centimetres of soil, and pupates there over the winter. The next generation comes up through that same soil the following spring, which is why the problem stays in one row of canes year after year and why forking the ground underneath in winter is worth doing.

Why autumn raspberries escape

The beetle’s egg-laying runs from late May to about the middle of July, tied to when the flowers are open.

Summer-fruiting raspberries flower squarely inside that window. Autumn-fruiting varieties flower from midsummer onwards, after most of the beetles have finished, and the fruit forms when the adults have gone. The result is a crop that is usually clean without any intervention at all.

Anyone who has fought this pest for several seasons on a summer row should treat that as the recommendation. Autumn varieties also crop when there is less other fruit about, they are cut to the ground in February rather than needing the old canes untangled, and they need no support in a sheltered spot.

Early blackberries sit in the same risky window and later ones largely miss it, so the same logic applies there.

What to do about it

Plant autumn-fruiting varieties, and treat this as the fix rather than as a suggestion.

On summer canes, hang white sticky traps with a flower lure at the top of the row in early May.

Fork the soil under the row shallowly between November and February so that birds and frost reach the pupae.

Pick every two or three days and take off the overripe and mummified fruit as well as the good.

Tap the canes over a pale tray during flowering and collect the beetles that drop.

Soak fruit destined for jam or the freezer in cold salted water for twenty minutes, and stop worrying about it.

What it gets mistaken for

Grey mould covers the whole berry in a soft grey felt and spreads to the fruit touching it. Beetle damage is dry, firm and confined to the stalk end.

Capsid bug feeds on the flower earlier and leaves fruit hard and lopsided with nothing inside it.

Raspberry cane midge produces splits and darkened patches on the canes near ground level rather than damage to the fruit.

Earwigs found sheltering inside ripe raspberries during the day are eating very little and are worth leaving alone, since they take aphids off the same canes at night.

Birds strip whole fruit and leave the plug bare on the cane. The beetle leaves the fruit in place with a patch spoiled.