Maybe she meant insecticide, slug killer or treatment for sooty mould or the like!

It's hard to comment because I've no idea what's meant by 'treatment', but if she meant fungicide or pesticide, there's no reason why such treatment shouldn't be done at the same time as fertilising. However, in terms of fertilising, permanent planting shouldn't be fed past June (with a couple of bulbous exceptions), though its fine for things like summer bedding.

I also don't see why they can't be done at the same time, though I wouldn't mix a foliar feed and an insecticide or fungicide in the same sprayer. At best, the fertilizer would degrade the "treatment". At worst, the chemical reactions could produce explosive or noxious gasses!!

Thank you. She said that she had silvery marks on her leaves of her new honeysuckle. She said she was going to ask for advice a the GC about treating it and at the same time was going to give it a foliar feed.

Working on the maxim, 'if in doubt say nowt' I did not comment,but was interested in what others thought.

Ah, well I wouldn't recommend a foliar spray feed at the same time as a pesticide spray, no matter what the time of year, as Tug already says...