Notes from the Garden Shed: September 2016

Unaccustomed as I am to giving weather forecasts, I’m tempted to give it a go after reading about this year’s direction of the quasi-biennial oscillation - don’t worry I’d not heard of it before either!

This quasi-biennial oscillation (or QBO) is a giant belt of air that runs around the world up in the stratosphere, 15km up. It used to switch directions regularly every 14 months and it's been watched doing this for the last sixty years. When running easterly, it brings us cold winds from the north, but recently it seems to be stuck in a westerly direction that boosts the jet stream that brings mild, wet, stormy weather. So another mild winter?

The quasi-biennial oscillation winds

The quasi-biennial oscillation winds

As reported generally, it’s been another poor year for butterflies; whether due to another wet spring or chemical farming we can argue all day, but one story has lifted the gloom by showing what’s possible. This is the resurgence of the Large Blue, a species that became extinct in the UK but after a reintroduction programme we now have an estimated 10,000 sightings this year – surely if we can do it for one species we can do it for others!

Large Blue (Maculinea arion) - The largest and rarest of our blue butterflies

Large Blue (Maculinea arion) - The largest and rarest of our blue butterflies

Bumblebee Conservation Trust's Bumblebee of the month - the Forest Cuckoo Bumblebee (Bombus sylvestris)

Bumblebee Conservation Trust's Bumblebee of the month - the Forest Cuckoo Bumblebee (Bombus sylvestris)

Hawthorn bushes loaded with berries

Hawthorn bushes loaded with berries

This year it was well-reported in the news that we’ve just passed the autumn equinox – nights now longer than days so into autumn or, as they say in America, ‘fall’. I would say we’re in the full season, not fall - well not quite fall yet! If you look at trees and bushes now, that dark green colour of summer is now tinged with warmer hues, brown leaves, red berries and seeds. 

One tree which looks like it's in autumn leaf fall - but isn’t - is the poor old Horse Chestnut, which is being attacked by the Cameraria ohridella moth. This species has a caterpillar that lives inside the leaf of the Chestnut, eating its way through the soft tissue but in such number that it damages the leaf.

Interestingly, this is a new species of moth thought to originate in Macedonia and first recorded in the UK in 2002 in Wimbledon. It is now spreading across the country. Because it’s a new species here presently, there doesn’t seem to be a suitable predator to control numbers. Luckily, the trees are coping and produce new leaves in the spring. I predict that when the trees rings are measured, these years of moth attack will show as very thin growth rings.

The leaf miner moth  (Cameraria ohridella)

The leaf miner moth  (Cameraria ohridella)

The moth’s caterpillar inside the leaf eating the soft tissue

The moth’s caterpillar inside the leaf eating the soft tissue

Horse Chestnut leaves showing the damage done by the moth’s caterpillar

Happy successional seed-sowing – now is the time to sow winter vegetables. This year, we’re sowing oriental leaf vegetables like Pak Choi, Mizuna and Mustard.