Any clue what's wrong with this?

The plant is Spiraea Douglasii (not a favourite of mine, friend gave it to me and it's quite useful I suppose as flowers late in the season). Not a clue what's wrong with it other than it could be the result of hellish late frost? it gets hard pruned every Spring but never had a problem with it before. Definitely not weed killer and couldn't see any insect infestation. Can't believe frost would cause the yellow spotting on the leaves. Had the shrub for about 6 years and all the other shrubs in the same bed are not affected. Hope someone can tell me what's up.

 

Hi

Is it all over effecting the leaves or just the odd shoot

 

Hi @Spruce. Thanks for trying to help. The majority of the shoots are affected and the leaves have yellow little spots about 1/2 way down the plant's stems. Most new small stems ie new growth this year seem pretty well ok, so could well have been those severe frost altho still iffy that they are responsible for the spots.

 

@silu

have a nose at this link

http://gardening.yardener.com/Problems-Of-Spirea