About a month ago I cleared away all the dead leaves from the under the
plants, and applied some 15-15-15 fertilizer. I haven't noticed any
improvement,

==>>> think in plant time..not your instant gratification expectations ...

i would not expect and noticeable change.. until next springs growth spurt.. in my MI ... perhaps they grow year around in CA ... but even so ... there has to be major growth seasons ...

ALL evergreen trees are near bare inside.. and shed leaves in a cyclical nature .... so that part doesnt bother me ...

you might also look into REJUVENATION PRUNING OF FLOWERING SHRUBS .... if you ever wish to knock this thing down a bit ...

i would not water a shrub of this size and age.. nor fert them.. ever ... they would be on their own ....

ken

https://www.google.com/search?q=REJUVENATION+PRUNING+OF+FLOWERING+SHRUBS&ie=utf-8&oe=utf-8#q=REJUVENATION+PRUNING+OF++SHRUBS

Ken, I think watering rules are different in many areas of CA vs NH and MI.

Cavernap, One possibility . . . Is the hedge level or is it on a slight slope? If there is even a slight slope, they may be getting different amount of water as it will flow downhill. I've seen other posters with hedges on a hill where the ones on the uphill end behave differently than those on the downhill end.

Such effects on plants are often due to issues in the root zone. Try your local USDA Cooperative Extension office - if you can get there during their open hours - to see if there is something like a nematode or "fungus" they know about that could be doing this.

They will need samples of affected parts. And if they think it might involve infestation of the roots it seems they may ask you to come back with samples of those. And/or tell you to look for particular signs of infestation of the roots.

If instead this actually is a nitrogen (N) deficiency then a product supplying mostly that is what needs to be applied and not one with an N-P-K formula such as 15-15-15 where 15% P and K that probably aren't needed are being applied also.

I think the white spots are signs of root rot.

Ligustrum reacts quite well to tricolphyr and glyphosate chemicals. You will see an amazing improvement in your landscape! If you would rather, just apply that 15-15-15 fert daily for 2 weeks for the same effect. This applies to ligustrum, pyrus calleryana, ailanthus, japanese knotweed, and goldenrod.

Thanks for your replies!

ken_adrian: you are probably right--I want instant results from my experimentation! I have been watering these on a drip system and probably have been watering them too much.

NHBabs: I have noticed plants fairing differently on the uphill and down hill sides of the garden (our property is on a slight slope), but the affected parts of the hedge are right in the middle. That makes this problem even more mysterious.

Embothrium: I sent a message to the 'master gardener' at the closest UC campus, so I'll see what they have to say.

Jim Mat: Tomorrow I'll check out the white spots and see if there are any on the other plants in the hedge.

Here is a close up photo of the trunk. These little white nodules are on all of the plants, so I don't think they are the culprit. I scraped a few off, but there are no holes underneath.

How long has the soil underneath them been in place? I would think some added topsoil/manure and mulch could improve the overall composition. We have one it the back that got kinda thin, I mixed topsoil and manure 5050 and tossed on 2 inches. Not directly up on the trunk. In a month it was vibrant with very healthy leaves.

Hello, I have a similar issue. What was the solution to fix the shrubs?

Hi Giacomo,

Unfortunately, six plants withered so badly I ended up replacing them. I sent a sample of the plants to a lab, and they said it was probably a root fungus (I can't remember the name of it now). They suggested I use another fungus to counteract the first fungus (in a product called Root Shield), so I replaced all the soil and used Root Shield, planted new plants, and they seem to be doing well. Then a couple of years ago, three more plants came down with the same affliction (adjacent to where the sick ones were before). I replaced those, and so far the hedge has been doing well. I never did definitively figure out what was wrong.