First, I'm an entomologist, so I can handle the spider mite question. I've never heard of this canker; if it's a plant disease, we have a Plant Diagnostic Clinic at NMSU that can either confirm this diagnosis or provide a more likely evaluation of the problem. While some good, in-focus photographs---general habitus and close-ups---are helpful, they will need some tissues to work on, too. Your best local source of info on plant problem diagnostics will be your Bernalillo County Extension Office---243-1386. Either Cheryl Kent or John Garlisch are likely contacts; Joran Viers is also a pretty good horticulturist and aware of info needs and sampling for lab analysis. There's no charge for these diagnostics.

Generally, however, once a plant has a genuine disease, it will have it until it dies. There might be some life-extending practices to employ but curing isn't possible. With our drought---and it will likely return, if not intensify---consistent, slow watering of each plant in the landscape is a must. 

As for the spider mites, these are likely Oligonychus sp. that focus on various conifers rather than the Tetranychus that attack just about any other broadleaf plant in the landscape. Drought is an environmental factor that favors spider mites; spider mites thrive in conditions that are tough for other organisms to survive. Dust from roads and even dust applications for certain other pests can favor spider mite colony success. If your trees were present during the February 2011 'Big Freeze' there is probably some unseen damage to them from that extraordinary event; that's certainly what seems to be happening with a variety of other trees---broadleaf trees and conifers, too---and symptoms of damage and decline can take years to be expressed. 

Spider mites are probably the worst pests to try to fight with insecticides since they may benefit more from these treatments than suffer mortality. Spider mites are prolific at reproduction and have very short life cycles---in the range of a week when temperatures are 'high' and perhaps 2 weeks when temperatures are a little lower (like spring temps). Insecticides also tend to kill natural enemies of the mites, giving the mites additional advantages for their efficient reproduction. This leads to another problem.....When people see that their first treatment didn't do much to the mite situation, they spray again---and maybe again. In these cases, what may not be apparent is the selection of mites for pesticide resistance.
If anything, the selection of active ingredients available to the general public for pest control is decreasing, not increasing. Changing brands or increasing dosage does not affect the pest problem, but may increase problems with these pests through selection for increasingly resistant populations. That's a genetic resistance that doesn't revert to 'normal' with the passage of time.

Damage done by the mites is permanent to that foliage. To have things look better requires the plant to drop the old foliage and put on new foliage. Putting on new foliage takes away from the food reserves of the plant. Many host plants put on new foliage and new growth once annually. Having to do so twice in a year is taking a double helping out of the plant's reserves. Even though we've had lots of rain in late summer, damage done in previous years as well as this year is still there somewhere in the background, with its impact on plant survival and appearance. And if the plant has some disorder on top of all of that, insecticide won't help that problem and whatever symptoms it may cause. 

With all of that said, spider mites I have seen associated with junipers, arbor vitae, cypress and the like tend to be active in early spring. As their populations build in warm weather they cover the foliage of the host with fine webbing that soon accumulates soil particles and small debris as spring winds blow. The webbing protects the mites from the elements as well as sprays. Damage and webbing are cumulative and any new foliage turns brown. The brown foliage will not turn green again; it has to be replaced by the plant.

One enemy of mites on foliage is rainfall---which can physically knock off the pests. Periodic power sprays of water may have about the same effect as rainfall; certainly the extra water is probably needed by the plant. The challenge here is whether you have the necessary equipment to do this sort of treatment. 

Beyond that, there are no systemic insecticide treatments that affect spider mites. They are not listed on the labels and have no effects on them.

As for insecticide labels, when looking for a product, make sure both the pest and the site (plant, in this case) are on the label. Then review the precautions for application and, if you're not familiar with the product, test it on a small part of a large plant or on a few plants out of a larger planting. If all appears OK, then treatment of the whole planting could be done. 

So many products for use by the general public contain pyrethrum or a synthetic but similar active ingredient. These are products most likely give modest, temporary control at best, but also reduce numbers of beneficial organisms and increase resistance in the pest population to this family of active ingredients.

Consider an insecticidal soap or a horticultural oil, perhaps containing the active ingredient Azadirachtin. There are a variety of products on the market now that have this active ingredient derived from neem trees. Basically, the oil is formulated for mixing with water and general broadcast application. Contact with a pest can result in its asphyxiation. That's a situation that's tough to develop any chemical resistance. This might be your best bet---but again, if the plant is diseased, that treatment won't help it.  

Spider mites are tough adversaries. I hope this information helps.

Thank you, Dr. Sutherland, for your most informative reply to the plight of Leyland Crypress Trees and for the sources of information available locally.

I have had three Leylands for no less than 10 years, planted from 5 gallon pots and have now reached at least 20-30 ft.  They were lovely and healthy until two years ago and since that time I have struggled to keep them well.  As you suggested, the drought we have been experiencing has played a big role.  A Diagnostician from a respected Tree Care Co. where I live came out and told me there were no treatments available.
Seiridium Canker is present, causing the browning of some limbs & also she noted spider mites which I could pressure spray with water to keep them under control and of course removal of the brown limbs (which is what I have been doing for two years now, along with consistent watering).  What is of concern now is 'leaf tipping'..
However, the Diagnostician did tell me that the my Leylands look better than any she has seen here in the City.  When she left, she said the trees had about 2 years left

A the time these trees were purchased from Rowland's, the nurseryman told me that they were not 'true' Leyland Cypresses.  I wonder what he meant by that fact; perhaps it gives them a chance to tarry on.

Again, thank you for your reply.     

I still say you need to collect specimens from these trees---have Cheryl Kent from the ABQ Extension office---243-1386---help you. Send them through the Plant Diagnostic Clinic here at NMSU and let's see what's what. My plant pathologist colleague here at NMSU is always leary of visual identifications of plant diseases. What we see are symptoms, but the cause may be different that what might be suspected. A headache, for instance, does not always mean the patient has a brain tumor. Also, in your case, giving the Leylands '2 more years' for life expectancy---well? Sooner or later everything dies, but if yours also rated among the best Leylands this person has seen---in the next breath, it sounds like---doesn't that make you wonder?

I still vote for sending specimens. When it goes through the Bernalillo Co. office with Cheryl, there's no charge for the service and results are returned promptly to the email address you provide on the form.

Hope this helps............later.............Dr. Carol Sutherland, Extension Entomologist, NMSU & State Entomologist, NM Dept. Agriculture

Thank you , Dr. Sutherland, for your directive to contact Cheryl Kent.  I did so Monday, 10/7/13 and left a message as she was out on an assignment.  I am awaiting her call back and hopefully we will have the Leyland specimens on their way to NMSU.
Unfortunately, (for the trees) (fortunately for me), I am recuperating after emergency, major surgery & unable to tend to the trees as needed.  Thankfully, my teenage grandson, when he mows my lawn also waters the trees.
  
I will keep faith the trees will become as the adage "All's well that ends well."
Joyce Anderson .   

10/15/13

To:  Dr. Carol Sutherland, NMSU
From:  Joyce Anderson:

Cheryl Kent came to my home today and took a limb from one of the Leylands to send to the Plant Diagnostic Clinic, NMSU.  The limb she took was from the most sick and the one which showed the first browning of its' limbs of which I kept removing so much that my consolation was it was being aerated.  I could only watch from my doorway & was alarmed to see she took a limb from the barest location.  The tree next to it, the middle of the three, is very full & large.  I mentioned my wonder why she didn't take from it......but she said the long limb she sawed off was dying--  I noticed that it did have some oozing at the joint. Guess I thought the specimens were going to be small clippings from each of the trees. (smile)  She mentioned the diagnostician from the tree place who predicted "2 years",  by her first name so i asked if she knew her & she does. Cheryl did not have a form for me to complete for the Clinic, said she would fill it out and  would call me when she got the report back.
She did say she could tell they had enough water or they wouldn't look as good as they do, however reiterated they would die but did not predict when.    I told her of Rowland's Nursery where i bought them & remembered the label on the buckets they were in had come from Washington State.
Again, thank you for all your help.           

P.S.  Cheryl did tell me the drooping down of tips was caused by an insect and were more a cosmetic problem.  I removed the reachable  ones.They are also increasing in number

Joyce Anderson  

I think we're beyond the questions here. Just waiting for the specimens to show up in the lab.