Dealing With Pear Midge Problems the Organic Way

Ordsall Hall’s heritage pear trees: 2x ‘Black Worcester’ and 2x ‘Williams Bon Chretien’ (and that’s a medlar at the back…)

It really hasn’t been a great year so far for fruit trees. A bitterly cold February and March gave way to a blisteringly hot, dry early April and then a return to hard rain and frosts in May. These sudden and severe changes mean it’s a tough time for fruit blossom.

A fruit flower is a reasonably hardy thing – it can withstand wet and wind pretty well – but in the face of the more extreme drops in temperature or exposure to showers of bullet-like hail, the delicate reproductive organs at the centre of the blossom can be damaged beyond repair. Once they’re dead and gone then so is they chance of that flower being pollinated. That’s assuming the pollinators are actually out and about in the first place of course which, given the conditions, they might not be just yet. And either way, no pollination means no fruit this year.

At Ordsall Hall’s heritage orchard we don’t have any plum or damson trees – early to set blossom, extremely vulnerable to unseasonably harsh weather patterns – but we do have some very lovely pear trees: two ‘Williams Bon Chretien’ and two ‘Worcester Black’.

Last year all four trees had to be manually de-budded in an attempt to control an infestation of pear midge by breaking the pest’s lifecycle. The midge lays its eggs on open blossom and the larvae hatch once the fruitlets are forming. They eat their way through the centre of the fruitlet, irreparably damaging it and causing it to drop to the ground. The the larvae tunnel out and pupate in the soil over winter, emerging next spring as adult pear midges to start the cycle over again. So the flowers had to go, before the fruitlets fell.

This year we were really hoping for a good response from all four trees, as well as minimal midge re-infestation. Early signs were good, with blossom cloaking all four pear trees, and plenty of it:

April 2021, pear trees in bloom, Orsall Hall, Salford

On closer inspection though, it’s clear that we haven’t entirely escaped our pest problems. Here are a few clearly distorted fruitlets that our Head Gardener, Jo Green, took from one of the ‘Williams Bon Chretien’ trees, cut open to show the damage inside:

Unfortunately, on close examination it looks like the Williams Bon Chretien may still be infested with pear midge.

That damage in the centre of each fruitlet has been caused by tiny, whitish-orange grubs that have hatched and are burrowing around in there, destroying any chance of the fruit reaching maturity. That means that at least some of the pear moth escaped last year’s attempted cull and lived to continue the breeding cycle.

We’re an organically-run site so we don’t use pesticide sprays, which means we’re going to have to try to break the life-cycle again, with a second year of de-flowering or at the very least, removing as many even vaguely distorted fruitlet as we can see. Which is extremely disheartening, and not a decision taken lightly, as it obviously means no crop at all again this year, but under the circumstances, it’s the right thing to do.

As for the ‘Worcester Black’ trees, it seems they might have escaped re-infestation by pear midge, although tests are ongoing, but they haven’t escaped the ravages of some of the frosty nights we had in April and May. Here’s a blossom cluster on one of the two trees, a couple of weeks ago, showing clear signs of some sort of die-back:

There are signs of frost damage in this ‘Black Worcester’ pear-blossom cluster

The two lowest flowers are clearly damaged and a couple of others may be as well: the dark centres, and the brown colour of the anthers – the pollen-bearing structures, which on the healthy blossoms are coloured red – show that these organs have died back. There are a couple of possibilities: one is damage by frost or pear midge, but the other is that the flowers have been pollinated already and the die-back has been caused by the organs simply reaching the end of their useful life.

A couple of days ago, the same tree was showing signs of plenty of fruitlet development, so perhaps pollination is the answer after all? On closer inspection though, some of the fruitlets are showing clear signs of distortion:

I removed this fruitlet and cut it open to investigate the cause of the damage. I was hoping not to see anything burrowing around in the middle of the fruitlet, which might necessitate a de-budding of this tree as well. Here’s how it looked, before and after slicing it open:

My camera’s zoom lens isn’t good enough to pick out that damaged section in detail, but after peering at it with my jeweller’s pocket magnifier, I was satisfied that there wasn’t a pear midge grub in there; presumably this was just a case of frost damage distorting the fruitlet, or perhaps partial pollination of some of the flower’s ovaries, but not others.

Observation of the trees will continue for the next few weeks and into the start of the summer. Jo and I will be keeping an eye on how the fruitlets develop, checking any that are badly distorted to see if they’re infested or if it’s just a physiological disorder, and then taking the appropriate action if it becomes necessary.

Fingers crossed though that the majority of the fruitlets stay clear of problems, develop well and ripen into a bumper harvest of superb ‘Worcester Black’ pears, surely one of the very best varieties for cooking and preserving; highly recommended if you can get hold of any to buy, or to grow yourself.

How about you? Any problems with pests or blossom damage? Please do feel free to share your tree fruit problems, along with and tips or solutions, via the comments.

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