For several months now something has been working its way down our hedge and killing shrubs one at a time. I did cut the hedge right back a few months ago and it now appears to be growing well except for the bits that are dying off.

 

MrsJ initially said a bug at the roots ... but she dug out and couldn't see anything.

 

Now she is saying some sort of fungus and has been treating it with ???? but they are still dying.

 

The pic which shows the 'death' ... a week or so ago it was not nearly as bad.

 

Any ideas what the problem is and what to do about it ... else I can see the whole hedge going!

The third photo shows a severely headed stem, a stub cut that has re-sprouted.  The stub has been infected with wood decay fungus that destroys the growing layer and conductive tissue and therefore prevents circulation of water and nutrients to the foliar growth.  At least that's what appears to be the issue at the one spot with severe die back in the photo.  If the entire hedgerow has been stubbed like that, then it may be just a matter of time before the other infections progress into die-back. 

 

There is no effective treatment that I know of for a situation like this except to keep the plants as healthy as possible in order to resist decay. Some of the foliage appears chlorotic (yellowed) due to nutrient deficiency. 

 

Other issues that can cause foliar die-back include root rot from over-watering, or the other extreme, water deficit (drought stress).  Pest infestations can cause dieback but that doesn't appear to be the case with your hedge from what I can see in the photos. The huge stub and associated foliar mortality is the only obvious issue. 

I had some perhaps similar issues with ornamental trees in my garden. I think the fungal infection may be be secondary and that the problem is an insect. 

 

I use the common Thai pesticide S 85. Spray twice a week for a month and see if it helps.

We're all just guessing of  course.

What's the soil like? I reckon maybe heavy clay soil, which is causing the yellow leaves and weakening the plant. In that case any fungal/insect activity will be secondary.

Some plants will thrive in heavy soils, so won't.

3 hours ago, cooked said:

We're all just guessing of  course.

 

True! But that may be all that anyone can do.

 

I had assumed that these had been planted for some time and had thrived before. But they do look like recently acquired "Mok", which should be pretty hardy.  

 

I have never had problems with Mok, but did recently have a fungal infection on some larger trees that resulted first in deformation of leaves and stems and then die back. 

 

The cause appears to be an invisible (too small) worm. And once I sprayed S85, everything cleared right up!

 

Thanks guys ... strange that it is working it's way from one end of the hedge. No problem yet with the hedge the other side of the garden which was cut back to the same level.

 

Yesterday MrsJ went to  Kasetsart University, showed the pictures and ask for advice ... she was given something to try ... I'll update on what it was and if it is successful.

 

The soil should be okay as it get doses of pig fertiliser now and againh... come from a relatives pig farm