Hydrangea with black/dark brown stem sections

I am trying to help a client with several old hydrangeas from her mother's garden. I have not seen them in bloom and don't have a variety identity, though I believe they are macrophylla. The environment is mostly mid day sun, with a watering system that does not 'spray' them.
The issue she is asking about, is that the past few years her plants have developed tip sections that get leaves, but the last (top) section will turn black on some and not flower.
My first inclination is to think it is frost related. In the north Atlanta area we frequently get late winter frosts after spells of warm wet weather. But I have always related this mostly to leaf damage.
This homeowner also admits to using landscape fabric, which I believe is detrimental to most plants, so I have advised they should remove this immediately and mulch with a 3-4" natural covering of pine needles and fertilize with a compost in May.
Appreciate any insight you experts may have!
Lyn
Georgia Gardenscapes

Is the landscape fabric directly around the hydrangeas' crowns or away from the plants? Are other hydrangeas in the garden having this problem? The plastic in those fabrics creates a water and heat barrier for the soil below, keeping roots at abnormally high temperatures. So I could see how the plants would be affected but not necessarily resulting in tips that turn black.

A fungal infection and winter damage could explain problems at the end of the tips but "turning black" sounds a bit rare. Is the owner applying winter protection techniques to these shrubs? What kind? Is she watering or keeping moist the protected stems somehow? Say, covering the shrub with leaves that get wet. Is she using any anti-transpirants during winter?

I did some additional reading and concluded that it would be rare for the problem to be caused by winter damage (frost) because the damage would be more widespread. In other words, why only the tips and not in other parts of the stem?

Unfortunately, the possible causal agent that I ran into is not a good one. Please research a fungal infection in hydrangeas called Botrytis (usually more common on macrophyllas). Also called gray mold disease, Botrytis can turn infected stems brown/black (not just the tip but the whole stem eventually). Leaves, petals and stems will exhibit damage. It is more common in greenhouses. The only way to confirm it for sure is to submit samples in a tightly sealed, transparent plastic bag to the UGA Extension Lab for analysis. It may cost about $25.

Here is a link to a sample picture of affected stems:

http://images.search.yahoo.com/images/view;_ylt=A0PDoS3FLVpRGX4AmzWJzbkF;_ylu=X3oDMTBlMTQ4cGxyBHNlYwNzcgRzbGsDaW1n?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3F_adv_prop%3Dimage%26va%3Dhydrangea%2Bbotrytis%26fr%3Dytff1-swat02%26tab%3Dorganic%26ri%3D6&w=220&h=147&imgurl=www.plantmanagementnetwork.org%2Fpub%2Fphp%2Fmanagement%2Fbotrytis%2Fimages%2Fdaughtrey6.jpg&rurl=http%3A%2F%2Fwww.plantmanagementnetwork.org%2Fpub%2Fphp%2Fmanagement%2Fbotrytis%2F&size=7.2+KB&name=Fig.+6.+Sporulation+of+%3Cb%3EBotrytis+%3C%2Fb%3Ecinerea+on+%3Cb%3Ehydrangea+%3C%2Fb%3Estems.+%28Courtesy+...&p=hydrangea+botrytis&oid=d44c176c370a5fb3499d3f3cfd402096&fr2=&fr=ytff1-swat02&tt=Fig.%2B6.%2BSporulation%2Bof%2B%253Cb%253EBotrytis%2B%253C%252Fb%253Ecinerea%2Bon%2B%253Cb%253Ehydrangea%2B%253C%252Fb%253Estems.%2B%2528Courtesy%2B...&b=0&ni=21&no=6&ts=&tab=organic&sigr=122qm2rsq&sigb=13ja17588&sigi=12gfh5ivv&.crumb=K6ZRC3C5iWV&fr=ytff1-swat02

Here is a link with information on Botrytis:

http://www.plantmanagementnetwork.org/pub/php/management/botrytis/

Does this help you?
Luis