Thursday, September 14, 2023

Egg Lay & Willow Rust: Important News

I'd anticipated that autumn larvae would be fairly numerous this year, but it looks as though I was wrong, again.  Badly. 

Initial searches suggest that the egg lay was low.  Certainly, larvae are hard to find, if not very hard.  It's relatively early days though, as I've been doing other things, but the signs are ominous.

It now seems that the females hadn't got into the swing of laying before the weather deteriorated in early July and, critically, that many of them were blasted away by the St Swithun's Day gale - before they'd laid many eggs...

Worse, far worse: the broader-leaved sallows in some districts have been severely affected by Melampsora Willow Rust.  I've been aware of this rust since 1977 but it's never been too much of a problem, swelling up in wet midsummers, but abating before autumn.  

This year, it's rendered most of the broader-leaved sallows in my home patch (Cirencester Park Woods) wholly unsuitable: many sallows there had dropped most of their leaves before the end of August, others were covered in golden leaves that are destined to drop early.  I haven't found a single larva of any Lepidopteron or sawfly species on infected sallows.  Here's what to look for:

Early Stage Infection -

Then it gets Serious - 

  Then this happens -

That photo was taken on August 21st!  It shows some resprouting, from a largely senescent sallow.  

Here's a leaf underside close up - 

All the broader-leaved sallows, plus the poplars and aspens in the Cotswold Water Park (another study site) are severely affected, but Savernake Forest and Bentley Wood (both recently visited) seem OK.  The pox seems to start at Junction 15 of the M4 (Swindon East).  

Crucially, narrow-leaved sallows (Salix atrocinerea & S. cinerea types / hybrids) seem far less affected. 

PLEASE LET ME KNOW IF YOU COME ACROSS OUTBREAKS OF WILLOW RUST.  We need to gather evidence (I'm liaising with Forest Research's Tree Health Dept. at Alice Holt Forest).  Email me on