We live in north Oakville, ON and have three ivory silk trees that are about 5-6 years old. They are in a southwest facing back yard on the north west side. They have bloomed profusely every year without fail until this past season the leaves seemed to turn and fell off of two of the trees and ended up bare about mid July..this spring being 2016 April all three have leafed out but the middle one appears to be bare in the center. There are no bugs or cracks in the trees we have them deep fertilized every fall along with other trees in the yard..we have someone come to look at it but nobody can seem to figure out the problem. We keep the mulch away from trunks.. They are in good soil there does not appear to be any moisture around the base of the trunk at all. We did see a few boulevard trees as well in the area that looked similar to what our trees did last season but none from the town had an answer either..any suggestions we are stumped..thank you in advance for any suggestions.
Ivory Silk Lilac Trees, Syringa reticulata “Ivory Silk”, are typically described as low maintenance trees with no serious problems. However, they, too, can be affected by some pest and diseases.
The wilting and leaf drop, as well as the bare center that you describe indicates clearly that something is wrong with your trees. It could be a pest like the lilac borer (although you would most likely have found a borer hole and some frass), or the fungus responsible for Verticillium wilt that damages your trees and causes the symptoms you describe. Another possibility is a nutrient imbalance in the soil.
It is almost impossible to further narrow down the problem without having a look at your trees therefore I strongly recommend that you contact a certified arborist. He/she will be able to diagnose what ails your trees and inform you about possible remedies.