Why do my baby pears turn black and drop off?

Pear midge has one generation a year and a very short life cycle, which is both why it is devastating and why cultural control genuinely works. Adults emerge from the soil beneath the tree in early spring and lay eggs in the unopened blossom. The larvae feed inside the developing fruitlet, which blackens and falls, and they then leave it, enter the soil, and wait for the next spring. Every stage of that happens within a couple of metres of the tree.

Step by step

1. Confirm it by cutting fruitlets open.Affected fruitlets are noticeably larger and rounder than healthy ones early on, then blacken from the eye end and distort. Inside are several tiny white legless maggots in a blackened cavity. That is conclusive.
2. Rule out the alternatives.The natural June drop sheds clean fruitlets with no maggots, later in the season. Frosted blossom fails to set at all rather than setting and blackening. Pear scab scabs the surface but does not hollow the fruit.
3. Pick off every affected fruitlet, as early as you can spot them.This is the control. Go over the tree several times through May, taking off anything swollen, blackened or misshapen, before the larvae leave and reach the soil. Bag and destroy them — do not drop them under the tree.
4. Collect fallen fruitlets promptly.Sweep or rake them up daily during the drop if you can. Larvae leave the fallen fruit quickly and enter the soil, and once they are in the soil they are out of reach.
5. Cultivate the soil beneath the tree in winter.Lightly fork or hoe the top few centimetres of soil under the canopy in late winter to expose overwintering larvae to birds and frost. It is imperfect but it reduces numbers.
6. Or mulch heavily instead.A thick mulch, or a membrane laid under the canopy from late winter to late spring, physically blocks emerging adults. On a small tree this is more effective than cultivation.
7. Keep it up for two or three years.Because there is one generation and the whole cycle happens under your tree, sustained hygiene reduces the population dramatically. One good year of picking off will not do it; three will.
8. Accept that a nearby infested pear undermines the effort.Midges will fly in from a neighbouring garden. If there is an untended pear next door, expect to manage rather than eliminate the problem.

Tips

• Affected fruitlets grow faster than clean ones at first, so the biggest fruitlets on the tree in early May are often the infested ones — a useful early clue.
• Trained pears against a wall are much easier to go over thoroughly than a standard tree, which is a real argument for a cordon or espalier if you have midge.
• Chickens or ducks allowed under a pear tree at the right time of year eat a lot of the fallen fruitlets and emerging adults.
• Insecticide timing is nearly impossible in a garden, because the target window is the unopened blossom and spraying open blossom kills pollinators. Cultural control is the realistic route.

Common mistakes

• Leaving the blackened fruitlets to fall naturally — The larvae leave the fallen fruit within days and get into the soil, where nothing you do reaches them. The whole point of picking off is to intercept them first.
• Composting affected fruitlets — The larvae complete their development and emerge from the heap. Bag them or destroy them.
• Assuming it is the June drop and doing nothing — The June drop happens later, sheds clean fruitlets, and leaves a decent crop behind. Midge takes almost everything and does it in May.

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