Last week I came to my garden, I was surprised looking at the small thuya. I brought it up from cutting, I cared for it all the time. What did I see that day? Dry yellow foliage and stems at the foot of the thuja. Looking closely I saw long black lines and spots on the trunk and thin stems. I was very upset.
I should learn more about thuja disease. Reading on internet I've found the Royal Horticultural Society (RHS) site and there is a complete description of this problem. It said that 'Cypress aphid is one of the causes of dieback on conifers. It has become an increasingly problematic on conifer since the 1980s'. 'A useful confirmation of aphid damage is the presence of a black sooty mould on the stems and/or foliage, as there are other causes of dieback on conifers'.
This description was absolutely similar the picture I saw. A black powdery coating of sooty mould developed on the stems and foliage. The lower parts were more severely affected than the top.
'Damage is caused by brown aphids that are active from May to November. They suck sap from the stems and even quite light infestations can have a significant effect. They are difficult to see as their colour matches that of the bark'
I've taken the pictures to look closely at aphids at home. I learned Cypress aphid often cause a gradual drying up of the foliage, by late summer many of foliage will be brown and dead.
Then I decided to find the active treatment (chemical or natural) against Cypress aphids. Reading different sources I learned some preparations and their analogues in Russia. I've found the insecticide cypermethrin, called 'Intavir' (Интавир) here. There are no natural preparation against this filth.
I did solution as it is said, and sprayed ALL stems and foliage. I had to spray twice, so I repeated it yesterday.
Here is the result!