A cure for what's killing our evergreen trees?

After two years of helplessly watching several evergreens and cedars in our ranch, some as tall as 20 feet, suddenly brown up and die, we may have found a cure. Yesterday, our eagle-eyed gardener Ulises showed me a frond from a Michoacán pine whose long needles seemed to be infested with reddish somethings the size of fleas. 

Infected Michoacán pine

His discovery was both alarming and reassuring: Though we may have spotted the culprit, it may have infected a couple of our Michoacán pines, very graceful, bushy evergreens with long needles that dance at the slightest breeze. They are not very common in the state of Guanajuato, and of all the trees we have, they are the ones I least want to lose.  

Sample in hand I went to El Surco, an agricultural products store in town, where a young, thin guy ran off to consult with someone and excitedly returned with an answer. It must have been his first day on the job.  

He said the problem is a fungus and prescribed spraying with the fungicide Chlorothalonil, sold in Mexico under the brand name Metanil. Further, he suggested a good dose of fertilizer and deep watering at the time of application of the fungicide. 

So I bought the Metanil and a 25-kilo sack of ammonium sulfate, an acidic fertilizer commonly used on evergreens, and gave the guy who waited on me a $20 peso tip that further revved up his enthusiasm. 

At home I consulted with Ms. Google, who seemed to confirm the young guy's diagnosis as well as his recommendations for spraying and fertilizing. The fungus seems to be the cytospora canker of spruce.

Infested trees.

Except cankers, as the name suggests, show as runny sores on evergreens, while the infestation here looks more like tiny insects. On the other hand, Google photos of infected evergreens closely resemble ours. 

And having no other possible solutions, for now I've gone with the Metanil fungicide. It is quite a toxic product, and I've equipped our gardener with latex gloves, a face mask and a light hooded nylon jacket.

Prognosis is guarded, quite guarded in fact, according to Ms. Google. She says sick trees often recover, particularly during the growing season which, I hope, is about to finally start in San Miguel. 

I've also sent a query and photo of the infested Michoacán pine to the University of Minnesota agricultural extension, whose website helped me with my search. I explained that while Mexico may not be in their service area, I used to live in Chicago which, eh, is kind of close to Minnesota.