I have 8 trees,two of which started truning brown and the needles are falling off,from the bottom up. Now it looks like it is spreading to the other trees. what can I do and can they be saved?
There are three usual diseases that will cause the foliage of Leyland's to turn. Seiridium Canker/Dieback, Botryosphaeria Dieback/Canker, and Passalora Needle Blight. Sorry most dieases of tree do not have common names.
Seiridium Canker/Dieback generally has the symptom of a bleeding canker on the effected branch. needles will fall off easily when a hand is run along the branch. Generally, the discolored branches are the symptom noticed first.
Botryosphaeria Dieback/Canker symptoms include dieback with branches turning yellow to brown in color – typically the first symptom noticed. However, unlike Seiridium canker, needles generally do not fall off when running a hand down a recently affected branch. Examination of dead stems often reveals more deeply sunken (often V-shaped) cankers that do not ooz sap.
Passalora Needle Blight
Typically, this disease only affects plant growth that is at least one year old. Symptoms usually appear during summer months. They include browning of needles and eventual needle drop. These symptoms start on lower branches near the trunk and then spread outward toward branch tips. Over time, the disease moves up the tree. The portion of a tree displaying symptoms may increase from one year to the next until only the tips of upper branches are still green or the tree dies completely. The disease will sometimes be more prevalent on one side of the tree then the other. No cankers.
I say all this because it is hard to ID foliage diseases from a picture and you will need to examine the branches as above.
Here is a web link to these diseases and the treatments for each. The good news if you follow the treatments the tree can be healthy.
I hope this helps.