Question
thanks for your advice, spring starts here 1st of Sept, so we have just started ,although our temps are in the mid 20s. We dont ever have the extremes of weather as you do, rarely getting below 15 durng the day in winter in Sydney - its lovely all year, and most plants grow throughout the year. We probably have more problem with hot weather (sometimes above 35-40c for several days in Jan/Feb, which is unpleasant and kills new plants. These plants have had new growth on them all year.
I have given them a very good water and a light Aquasol feed, and they seem to be looking happier (might just be wishful thinking.. but at least no more leaves are falling off.)
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Followup To

Question -
I live in Sydney Australia, I have a vibernum hedge that was planted about 8 months ago, plants now about 3 feet high. Some leaves are now changing colour from deep green, to a yellow colour, are wilting when yellow and then falling off. This is only happening to the lower leaves or those close to the trunks, and is happening to quite f ew of the plants although not all. Its happened over the last few days - our weather has been consistently fine with no cold or hot snaps (it is Sydney after all!)No herbicides have been used nearby and the plants have not been overwatered. I havent fertilised them for a while as its winter here, could this be the problem. Should I wait and see what happens? Any advice you can give would be much appreciated, this is a very long hedge and I am worried the whole lot will die off.
thanks

Answer -
Ahoy Sydney - you are approaching spring there now?  Boy I wish we were doing that here.  End of summer is the saddest time of year for me.

Vibernums come in many shapes and sizes, so I will give this answer my best shot, Anne.  I take it your leaves were green all winter, and now they seem to be waning.  Did I get that right?

Must also tell you in all fairness, Anne, I have no clue what the weather in Sydney is like.  I am in New York, and New Yorkers are famous for our ignorance of the rest of the world, I am embarrassed to say.  But it's the truth.

I would not fertilize any plant in the winter, when it is dormant, even one that is evergreen; it would not need fertilizer until spring.  How far are you into spring?

Do you notice any holes in the affected leaves, or is this simply a matter of changing color?

Browning and yellowing of leaves, with holes observed, are symptoms of winter injury where we garden here on Long Island.  The holes in the leaves appear where leaf tissue died, dried up and actually dropped through the leaf.  Older leaves are usually the most vulnerable; they finally succumb altogether and drop off the plant.  Newer leaves would be expected to be healthy and symptom free.  Since I am not sure when your new growing season would begin, or when your viburnums would resume grown, I think you would be wise to find a gardener in your part of the globe who can give you more intelligent answers on this.  I can, in all honesty, at best give you only an educated guess, sorry to say.

How does this diagnosis look to you?

Answer
Thanks for your update! One of the problems of long-distance gardening is that your climate can be so completely different that you may as well be writing from the moon.  I am in USDA Zone 7, and I can pretty much address questions to cold Zone 5 or 6, and down to Zone 8 - but not further.  The very name USDA is probably completely foreign to you.  And it appears, quite unfortunately, that your Viburnum problem is foreign to me.  I would love to know everything - some relatives tell me I behave as though I did - but I have so much to learn.

Very sorry!