Rhizosphaera Needle Cast
I need some help from the collective brain trust here.  I have a few Colorado spruce tress that have been diagnosed by a professional as being infected by Rhizoshaera Needle Cast disease.  They want a small fortune to treat these trees three times per year for at least three years (and possibly forever).  I did some searching and have decided that this is certainly something I can handle myself and save a bundle. 

My conclusion is that I need to treat them with a chemical called Chlorothalonil or Daconil.  They should be treated in mid to late May when the new needles are about half grown and then two weeks later and two weeks later again for three treatments.  The application should wet the needles to the point of dripping.   I have a 25 gallon sprayer on the back of my garden tractor with a wand that should work great for this.

So now my question.  All of these chemical labels say you need to apply it at so much per acre.  It seems this chemical is primarily used in commercial environments where they are spraying entire fields and it look like it is frequently used for grass diseases so I guess this explains why they call it out in acres.  I just want to know how much chemical to mix with 20 gallons of water and go spray the tree until it drips.  I can't find the answer to this question anywhere.  Does anyone here have experience with spraying spruce trees for needle cast that can give me some advice?
I use Docket WS (54% ai). Label is for 5.5 pints per 100 gallons....So 1.1 pints or 17.6 oz in 20 gallons. Depending on weather, you can get away with 3 week intervals just fine. Weather also dictates number of sprays. I tell clients to expect +/-3. A couple of years it dried out early and I only did 2. I was starting to think this was going to be a 4 spray year...But the warming has slowed back to a more "normal" pace.

How much mix do you need?: I plan on 3-4 gallons for a "normal" +/- 25' tree... Depending on your psi, gpm and nozzle, you may need more or less.

Anything you can do to improve airflow to the trees? Sounds like you have read up on the disease so you know not to let a sprinkler keep the needles moist?

Finally, check for spruce spider mites. They vector Rhizosphaera. It is rare I find it without evidence of them too. You need a miticide or horticultural oil (which will wash the 'blue' off of your blue spruce...Doesn't hurt the tree, but doesn't look good either) to treat them....Regular insecticides be really don't work. SSM and Rhizosphaera have been just hammering the spruce around here the last couple of years. You gotta be on them early in the cycle to keep the trees looking good.
I have yet to see any yard chemicals that do not include mixing ratios and directions right on the label of the container.
there are a lot labeled per acre rather than per gallon...especially when you get into the professional chemicals.
PS:  I should add if you are going to be treating for a few years, switch chemicals.  Fungi are more prone to developing resistance.  Switching chemicals knocks out any that might have thoughts of developing resistance.
JosephP, thanks so much for the valuable advice.  That is exactly the kind of help I was hoping to find.

Just a few follow up questions for you if you don't mind.

It looks to me like all of these are basically the same product - just one is a name brand and the others a generic versions from other manufacturers.  Do I have that correct?  And it looks like your recommendation is the least expensive of the bunch.  I have found a cheaper source for the Docket WS than Amazon at $132 with free shipping.

I have other spruce trees that currently don't appear to be infected, or if they are it is to a much lesser degree.  Is there any reason to spray them proactively, or should I wait for symptoms and then spray only if necessary?  With the 2.5 gallons I will have plenty of chemical to last for a few years.

Will the chemical last for a few years, or do I need a fresh supply each year?

You mentioned changing chemicals to avoid developing a resistance.  What would an alternate chemical be?  I have seen copper octanoate mentioned as a fungicide.  Is that an option?  And then finally how many years can one go before he needs to change to  a different chemical?

Thanks again for being so helpful.

Edited to add location: I live in Rochester, MN if that has any bearing on any responses.
Yeah...all those look to be the same with the same active ingredient.

TreeStuff has Chlorothalonil

I'd treat the other spruce at least one year.  Remember, fungicide is NOT curative - it is only preventative.  Think of as "anti-fungus paint" on the new needles.  You aren't curing your already-infected needles, you are protecting your new ones.

Mancozeb is also labeled for Rhizosphaera.  If you go through one 2-3 year treatment cycle and knock it out, I'd be satisfied.  If it comes back within  a few years switch products for further treatments.
I don't know about where you're at, but here fungus' infect mostly weak trees. I would consult someone to see if some systemic method works along with feeding or treating the cause of stress on the trees. Just a thought.
Apologies in advance for taking this a bit off track...but since the tree doctor is the house....

I have a couple flowering/ornamental cherry trees that for the last three years have been developing rust-colored leaf  spots that start to show up in the summer, followed by leaves falling a month to six weeks early. I'm assuming fungus and have been spraying Daconil just after it leafs out in April, then again a month later, but it doesn't appear to have done any good. The spots start out rust, turn brown, then the leaves turn yellow and drop in August - and trees a hundred yards away appears to be unaffected and drop leaves much later.

Without better description, it sounds suspiciously like a fungal problem. How do the flowers look...do they ever look rotted? Any dead limbs or twigs? Perhaps start the treatments a little earlier and keep the treatments closer together. As suggested above, switch fungicides. Agrifos, Eagle, and Captan all tend to do well on foliar fungi on the fruit trees.

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