Tatarian dogwood, Cornus alba, is moderately to highly susceptible to a cosmetic leaf spot (yes, fungal in nature) and both the common white variegated forms - Ivory Halo ('Bailhalo) and 'Elegantissima' (syn. Argenteomarginata) - are especially prone. This is usually exacerbated by wet conditions (earlier heavy rainfalls) or overhead watering.

While it is sometimes severe enough to result in near defoliation, it is not a serious problem and does not require treatment.

Often with fungal diseases it is recommended to practice good sanitation after leaf fall - be sure to clean up the dropped leaves rather than leaving them as a natural mulch. It reduces the number of fungal spores remaining for next season. I don't know that this is recommended for dogwoods, but it makes sense to me.

what they said.. and beyond that ... its fall .. and its a deciduous shrub ....[the leaves fall off]

the leaves are tired.. and shutting down due to waning sunlight.. and temps will be falling ...

i am not much impressed by leaf damage.. this time of year ...

and dont forget.. it was extra stressed this year.. due to planting ...

this is a shrub... there is a shrub forum ... just in case you have future questions about shrubs ... as you got your answers here on this topic...

ken