Sudden onset of Black leaves and branches on Holly bush that is 3 feetx 4 feet tall, about 12 year old. Predominant sun with no pesticides or fertilizer applied. 90% of one plant ha been affected and another one that is perpendicular in placement to #1 has about 20% on bottom.(which was not evident yesterday) In taking pictures, there is a sticky substance I felt touching the leaves. My question is, how to I stop what is happening, and treat what is here. I have read some things on line about washing leaves and bush with soap and water and applying a horticultural oil. What should I do and in what order? Thank you in advance