yew hedge disease?

A nice yew hedge at approx 6-7 ft high.
2 of the 'plants' next to each other are stunted and now show signs of yellowing, going brown in some places. Can this be some sort of disease or just lacking moisture. The sub-soil is clay based. Any ideas??

 

It's possibly phytophthora - have a look at the RHS comments on it.....

"How Phytophthora affects the garden

Introduced to the garden in various ways - on infected plants, in irrigation water, in soil or windblown dust - the fungus may remain dormant in the soil for many years. Most often during wet weather or on poorly drained soils, infection may occur through the roots of susceptible plants, which are killed. The foliage shows symptoms only when the root infection is well advanced, with the production of small, sparse and yellow leaves and eventually some die-back. Infected roots are black or dark brown, and fine roots are absent. Secondary infection of dead tissues by other fungi is common.
What to do about Phytophthora

Where the disease is new or localised in a garden, affected plants should be destroyed and the soil from the root-run should be replaced with fresh topsoil, or treated by a contractor with a chemical soil sterilant. There are no soil sterilant products available for amateur use. Replanting should be done with less susceptible species, which will also benefit from measures to improve soil drainage. "

Yew is susceptible to it, so it's definitely a possibility. I've seen just the odd plant in a hedge affected, and that has to be taken out, root and all, to avoid it spreading. I hope it isn't that, but worth checking.

 

David, some of the phytophthora diseases are notifiable, so if you have any suspicion that that is what the problem is with your hedge you should report it to DEFRA just to cover your back. David.

 

Thanks to all for the replies. I'd post a picture but I cant see an obvious solution