Leland Cyprus dying

Asked July 8, 2019, 6:27 PM EDT

My Leland Cyprus are slowing dying one by one. It starts with the tips falling off and then more turning brown along the branch. The trees then die from the top down. I did find some very small holes the size of a pencil led but cant find any bugs to speak of. I have a whole hedge of them and am seeing this progress from tree to tree. I tried using a systemic around the soil but that didn't seem to help. Do you have any suggestions? Thank you for your help, Lisa Abernethy

Jackson County Oregon

1 Response

We're sorry to hear about your trees, Lisa, and unfortunately, there is not much you can do once the major portion of the tree browns out and dies. Leyland Cypress is a naturally occurring hybrid between an Alaska cedar and a Monterey Cypress. The drought of the previous 5 years has weakened many larger Leylandii trees, making them subject to invasion by insect pests, notably a tip moth. In the case of your trees, no insect was found in the holes you saw because the larvae that had been laid on that branch tunneled out, formed a cocoon, and became the descendant of the moth that laid the eggs in the first place. Had you been able to identify when the moths were present and sprayed for them, you might have had some success in lessening the problem, but timing is very difficult. We have had some personal success with clipping back "broken" or dangling tips and carefully raking up all prunings and fallen tips and destroying them. You can also use the systemic soil drenches (usually Imidacloprid) that are available. Follow the label directions exactly, especially as they refer to timing the drench(usually early spring and again in August.) This treatment frequently involves measuring the girth of the tree at waist level and calculating the proper amount to use. This treatment is not inexpensive, especially if you have a lot of the trees. Do remove any totally hopeless cases and destroy the wood .Do not store it as firewood. You can find further information and other suggestions for dealing with the pests by checking the Oregon State University Horticultural Dept.website: http://oregonstate.edu/dept/nurspest/cypress_tip_moth.htm
We hope you will be able to save some trees; if not, check out your local OSU Extension Office (541-776-7371) for lists of less vulnerable trees.