Hi I'm a new user, so bear with me if I've not done this right. But I have a question that I have not been able to get an answer to. I have a sick holly tree that I would dearly love to nurse back to health. I'm not sure what the problem is, but the leaves are spotted with black and yellow and there are deformed branches. What do I do? Can/should you use a dormant oil/sulphur on it? Thanks for any help with this
Although there are a number of holly problems that are universal, some are more regionally restricted, and it's helpful to let us know where you are gardening. The most common holly disease in the Vancouver area is Phytophthora ilicis (leaf and twig blight). Disease symptoms include black blotches on the leaves and leaf drop, which starts in the lower branches in the autumn and proceeds upward during the winter. Twig cankers and rotting berries are also sometimes seen. Infection and disease progression are rapid and control is difficult given high winter humidity. Crowded conditions and poor air circulation are conducive to disease spread. Pruning out affected branches is often recommended, but if damage is extensive, pruning to ground level may be a sensible option (hollies are renowned for their ability to produce and regrow from stump sprouts). Fungicides may be effective in slowing down the disease, but generally the bulk of the damage is already done by the time the problem is noticed. It is always better to not rely on fungicides (including materials such as lime-sulphur), as the plantings can become dependent on regular treatments. An alternative approach is to allow plants to develop inherent resistance or tolerance to pathogens and to encourage the presence of competing or antagonistic organisms that naturally supress disease-causing organisms. Using best cultural practices (i.e., providing optimal growing conditions and encouraging biodiversity) is the way to facilitate stronger, more pest-resistant plants.
