I have noticed that two different plantings of Zelkova serrata trees (that I specified!) are showing signs of dieback of the upper branches. The trees were planted as 6cm and 3cm caliper size, 3 years ago, and all were irrigated their first year. The first year they showed some dieback, and this year some are almost totally without leaves except for new leaves along the lower trunk. The smaller trees had been in root bags, which were removed on planting. The larger trees were either B&B or in wire baskets. The larger trees are in a commercial planting on automatic irrigation. There is no obvious sign of insect damage. What physical stress might be causing this dieback? Literature seems to indicate that the Zelkova is a good tree for tough urban situations... Thanks for any advice!
Your problem is indeed perplexing as the Zelkova's are indeeed quite adaptable and tough. There is some concern that the Zelkova's are not as resistant to Dutch Elm disease as once thought, but this disease is very uncommon in the lower mainland of BC, assuming that is where you are. Real drought can be a problem and can cause bacterial cankering but that is uncommon as well. If you are not in the greater Vancouver area, you might ask at a local nursery if Dutch Elm disease is a factor in your area. Shallow soil - which is not having a sufficient depth of soil for the trees liking is also a real problem for Zelkova - there should be a minimum of 2-3 metres, and the trees would prefer more. I suggest you consult a certified arborist to come look at the trees. Good luck!
