Maybe the info at the link will help you identify the cause.

"Spores of the fungus are spread to other parts of an infected tree, or from tree to tree by water splash from rain or irrigation."

Here is a link that might be useful: Leyland Cypress diseases

Interesting reading, but depressing too. This could one of those cases when you think you are doing right, but in reality you may be completely wrong.

For the 1st week or so we used soaker hoses for watering, but it was obvious that they were not geting enough water. We don't have good pressure here on top of the mountain. That's when we switched to the sprinklers. Due to the lay of the land the sprinklers are set on the South side, and with this type sprinkler, the spray contacts the trees from about 4-5 ft. down near the ground as they cycle back and forth.

I'll bet it is no coincidence that the major browning started on the South side and is spreading. Should I stop watering for a week or so, or at least change to hand watering at the ground level?

I've uploaded several images to Photobucket if you view them.

Here is a link that might be useful: {{gwi:362621}}

Could not view the trees.

Leyland Cypress are quite prone to several diseases, as you have learned. Phytophthora is one that is VERY common in clayey soils, and Leylands must never be over watered.

The file size is 244 kb which will take some time to load for someone with dial up connection.

{{gwi:362622}}

Here is a link that might be useful: Trees

The file size is 244 kb which will take some time to load for someone with dial up connection.

{{gwi:362622}}

Here is a link that might be useful: Trees

My grandparents planted about 200 of these along their property line to block the view of a new school being built next door. About 1/3 of them ended up dying and now there are obvious gaps. They were told some kind of mite gets in them, I can't remember what kind though. I agree watering every other day is too much in clay soil. Once every four days may be okay, as long as it doesn't rain.

I can tell you right now the problem is the sprinklers. Yes, they need water, but you can NOT keep the foliage wet, or it will breed fungus. A soaker hose is your best bet.

In fact this applies to most evergreens. They just cannot take getting their foliage wet.

I was afraid someone was going to tell me this after reading more about the trees. And this is our fault for not educating ourselves more. However, you would think that the tree grower would tell buyer's things like that, maybe even give you some specific instructions.

Given this, what's the chances of recovery, and are there things we can do to improve that chance? Should we continue watering or let mother nature take charge?

I'm late to this thread, but wanted to add that the size trees you bought are not 'adult' or 'full grown', not by a a long shot. Leylands are monsters, and planted too close together will die of fungal diseases.

Since you will have to eventually remove at least every other tree to allow for the natural growth spread of this variety, maybe you can do some culling now, or as soon as you see which trees are not surviving. The others will fill in.

Whoever sold you so many trees planted far them too closely for their ultimate full grown size.

Dripping at the root once a week for a long period of time is much better than watering everyday. That way it gets deep into the roots, but these trees are famous for fungi and for making knees and they do need to be farther apart. The close proximity will breed fungi.

Sorry for the delay. My main PC crashed this weekend and I'm not happy.

Before I catch you up, thanks for the replies. The trees look about the same, no better and not much worse. Only 1 tree looks dead for sure now. I stopped the sprinkler watering about 10 days ago and they got 1 small rain last week. I hand watered yesterday for 3 hours across the 40 trees, avoiding wetting the foilage.

Should we attempt trimming any of the brown foilage, and if so, how far back (the entire limb, just brown spots, etc), and should we remove the 1 that appears dead?

Feed and water the soil; never do that to the plants. The plants will use it at their discretion. Do as much organically as possible and cease buying "fast growing" shallow rooting plants.

A mid summer update.

As you may know, we are in the middle of the 2nd driest year on record here in NA. Given that, I have been watering about every 5 days with a soaker hose for 12 hours/50 ft.

Although we have lost 4 trees, the others are hanging there and look better. In the last two weeks we have received a few good showers, including today, so this should help. More rain is on the way again tonight and tomorrow.

Larry, I have a "browning" problem with my Leland's also. My trees are planted close together. I noticed your question about trimming out the dead parts and cutting out the bad trees wasn't answered, ever get an answer to that? I'm thinking about cutting down every other tree, but want to hear what you did and if it worked. If you get a chance, let me know, it would be a big help.

" Currently there are no chemical control measures recommended for the disease in the landscape or nursery. Avoiding water stress and tree wounding may reduce infection. Infected branches or twigs should be pruned and destroyed as soon as symptoms are noted. Prune at least one inch below the canker, and sterilize the pruning tools between cuts by dipping them in rubbing alcohol or in a solution of 1 part chlorine bleach to 9 parts water. Tools should be cleaned and oiled after using bleach to prevent rusting. Severely affected plants should be removed and destroyed."

You may want to read all of the info at the link

Here is a link that might be useful: Leyland Cypress Diseases

On some of my leland cypress I have some limbs that are browning, which I believe came from the pines from across the road. the pines have eventually died and I want to know if there is a spray to prevent from passing on. Please help me.
Thank you Stacey Worthington

organic_larry- Can you please share your experience, I have the exact same problem. Planted in Jan 2017 and started turning brown 30 days later. I have a total of 18 lelands (almost same size as yours): three completely brown, one brown from the bottom and one brown from the top.

I have found that if I spray a broad spectrum of micronutrient once in the growing season it helps the browning problem on mine. Not sure which clay you have, but clay tends to be acid and have aluminum issues so some lime is probably in order to unlock the existing soil value by converting the aluminum to inert gibbsite. If you have a fungus it would be in a lot of them, not oney twosy. I just crush womens (iron) multivitamin into water because no time for all that, but there are companies like hi-yield that make sprays of that nature.