Black currant leaves gone red

Any ideas why my black currant bush has deep red leaves this year? They're usually green. The bush has been in the same spot for years. Nothing else has really changed. It is forming fruit as usual. In the same area the red and the white current bushes look perfectly normal.

 

With what did you mulch since last years harvest?

 

Nothing. I might have put down a dusting of wood ash from the fire bin, but I haven't done anything different to what I always do.

 

Maybe needs watering? It’s been very dry.

 

Would suggest that you maybe have a deficiency in organic matter and/or potash. Well rotted farmyard manure at 4kg/sq metre annually, after picking and pruning.

 

I think the most likely explanation it's just the heat. I haven't ran the sprinkler the summer yet, and while I've been watering, perhaps not enough given the heat and lack of rain. The odd thing is though is other currant bushes nearby in the same area are all lush green.