Can you just cut off a representative sample of the damaged portion of the foliage and take a close up photo? The above is a bit too indistinct to make a good determination.

Without a closer view, I'd say these look a lot like male pollen cones, so perfectly natural, but need close up to confirm. Pollen cones don't hang around year round and they would affect all your thujas to some degree or another so not sure if this is the issue

Close up photo please!

ignore it.. its actively growing just fine ...

but do give gal the pic.. for further analysis ...

never in my life.. have i head of these type plants needing to be neemed ... but i am in MI ... perhaps you were sold a useless product ... but he made his boat payment ...

are you aware of how and when to apply horticultural oil ... ???

it needs to contact a problem.. to smother it ... if you have no problem.. then all you were doing was coating your plants in oil ... and i hope you werent doing that in summer ...

ken

Thanks gardengal48. I am attaching picture of the infected shrub together with non infected for comparision. The infected shrubs are all covered with those 'bumpy tumours', the healthy ones are all green. They look very ill, and it doesn't look natural at all. The infected shrubs are directly next to the street and are spreading inwards.

Thanks Ken for your reply, too. I put the oil in late fall and winter during non rainy time. I hoped I will see the results in spring... Unfortunatly, i don't see any. I found somewhere i should cut all affected branched and burn them. It would mean i need to cut it all as the whole shrub is affected.

Looks like over watering to me. Improve drainage or cut back on watering and spray with a fungicide like daconil.

Frank

OK - that's not a water issue and even if it was, fungicide is not the solution for that sort of problem.

Arborvitae tend not get a lot of disease issues but Berkman's blight (Coryneum berkmanii) is one that can do some serious damage. My suggestion would be to take a sample of the affected foliage to your local extension office for an accurate diagnosis. If confirmed, they should suggest control measures but typically it involves pruning out the affected tissue now and then spraying to control development of the fungal spores, usually in early fall.

A preferred fungicide would be a copper sulfur application, not so much the Neem oil. But get a confirmed diagnosis first before attempting any other home health care :-))

FWIW, as long as drainage is good, it is pretty near impossible to overwater Thuja orientalis......one of its common names is swamp cedar. Typically, inadequate watering is more of a culprit for arborvitae problems.

Thanks a lot, i really appreciate you helping me solve this puzzle! I've been researching in the last few days very intensly online, and it looks to me like effect of false spider mite ( i am not saying it is). The little branches not only changed color but they look look deformed/mutated. I looked closely using a magnifying glass but didn't find any traces of larvae or eggs. I found one adult micro bug, but have no idea if it is related at all.