I was writing about Leyland Cypress last week and ran out of space. If you missed the column, it is available at possumsupply.com under the Horticulture Hotline tab.
Leyland Cypress can get some diseases that are treatable and some that are not treatable at this time. It is very important to correctly identify what disease you have before you spend time and money trying to manage something that you cannot control (this is true with any plant, insect, weed or disease). Depending on the size of the tree and your equipment, a professional may be your best option.
Unfortunately, when treating the diseases of a Leyland Cypress, pruning out diseased limbs is usually the first step; therefore, ruining that pyramidal form you were after when you planted the tree. Disinfecting your pruners with a 10% bleach solution between cuts will help prevent the spread of diseases.
Culturally speaking, Leyland Cypress like moist but well-drained soil, lots of sun and air movement, some fertility, and they do not like overhead irrigation (wet needles lead to disease). If you can grow them in these conditions, they have a better chance to survive.
If your Leyland Cypress is dying from the bottom near the ground and moving upwards, you could have Passalora Needle Blight (also called Cercospora or Cercosporidium).
Try to improve their cultural conditions, prune out effected branches, and spray with Thiomyl, T-Methyl or CuPro. The good news is you can treat it. The bad news is you have to remove the diseased lower limbs.
Seiridium canker (my spell check loves all these disease names) is probably the most common disease out there and is easy to identify; however, there is not a cure for it at this time. The ends of the branches are an orange / reddish color. There are usually random branches throughout the tree that have these bright orange needles (in a way the way twig borer manifests itself on a Magnolia – just referring to the random aspect – one is a disease and one is an insect). You can also look for cankers and resin oozing. Trying to keep the tree as happy as possible with good cultural practices and removing diseased limbs are about your only option at this time.
Looks like I’m going to run out of space again. With all the rain earwigs, big roaches, and a few other uninvited guest are making their way into our homes.