In my experience, deep root feeding has both benefits and drawbacks. If a deficiency of phosphate or some micronutrients is a problem, injecting it into the soil is the quickest way of getting these relatively insoluble nutrients down to the roots. On the other hand, injecting them more than a foot deep is probably futile, since most of the feeder roots are within the top 18 inches of soil. Also, trees respond much better to nutrients spread evenly through the soil, rather than concentrated in a few small spots. I prefer to spread fertilizers evenly over the tree's root area, top them off with an application of humates to keep them soluble, and give a deep, even watering--up to 3 feet into the soil--to push the sodium down below the roots. Deep root feeding is one of those techniques that is good for a limited number of conditions, but is sometimes marketed as a panacaea to milk more money from the homeowner.

As for microinjections, depending on what chemicals they inject, they may be the only way to save mulberries that are so far gone into sooty canker.

Other factors may be affecting your trees, too. How are you watering them? Many of the older trees in Arizona started out in yards flood irrigated with SRP canal water, or on lush, frequently sprinkled lawns. Unless done carefully, switching from SRP to tap water sprinklers, or from irrigation or sprinklers to gravel and drip, can cause a slow but steady decline in tree vigor and disease resistance. Another problem people have been having is that they haven't been maintaining their irrigation berms, resulting in a gradual reduction in the depth of irrigation, and increased salt and drought damage. Double checking your watering system, and bringing it up to specs, is a simple way to cure common tree "diseases".

Hope this helps!
Kevin : )

Mulberries are a short-lived tree, so they are near the end of their lifespan. Removing the diseased trees and replacing them with something that is more tolerant of Arizona's soils and water availability would be much better for your property values than spending any money on the mulberry trees. Anything they are doing for your landscape can be done better by many other trees.

As for the Jacaranda ... they respond very well to light fertilization with high nitrogen fertilizers, spread arouns the canopy area and watered in well. As the guy above me said, the feeder roots are not deep at all.

The jacaranda's leaves are about to fall off, so that "expert" is basing his "diagnosis" on leaves that have been through one heck of a winter.

Thank you for the advice. I'm new to gardening, so I have much to learn!

Our lot does not have flood irrigation. The jacaranda lives in a grass lawn that gets sprinkled 3x a week during warm weather. We don't have any irrigation system in the backyard yet, so the mulberries are watered by garden hose. I'm 99% sure we're not giving them enough water.

My husband has finally agreed to have one of the mulberries removed... neither of us can bear to part with both of them just yet. We are thinking of replacing it with an aleppo pine.

We got a bag of 16-4-8 fertilizer for the jacaranda. Should we apply it now or wait until the ground has dried out a bit?

Great advice from tugbrethil and lazygardens. It's always best to spread granular fertilizer on moist soil and then water it in. Since soils are moist now and your Jacaranda is just about to wake up from winter why not apply your fertilizer? If it doesn't rain any more, just water the product in with your sprinkler system or hose.

I'd recommend you deep water your Jacaranda once every couple of weeks in summer in addition to the sprinkler water.

As for your mulberry trees, sooty canker is a fungal disease that enters the tree through wounds - often caused by pruning. It can also be transferred on tools from tree to tree. Mulberry trees used to be pruned back heavily every year which put enormous stress on the trees, plus created a perfect situation where sooty canker (and other pathogens) could affect the trees. As a result, these trees don't live long.

If you remove one of your trees, choose a replacement that will fit into the space allotted. Aleppo pines can grow extremely large. Have you considered a Chinese Pistache? They are deciduous, like your mulberry, but have striking fall color. Just a thought.

Here is a link to Landscape Plants for the Arizona Desert on line. www.amwua.org/plants

I've also inlcuded a link to the U of A Plant Pathology web site with information on sooty canker.

aztreelvr
Certified Arborist

Here is a link that might be useful: Sooty Canker in Mulberry

Thanks for the links and advice, aztreelvr. It's nice to get an opinion from an aborist who isn't trying to sell me something. The fertilizer went on today.

The Chinese pistache is beautiful. How much do they typically grow in a year? We need a fast-growing tree since the folks behind us light up their yard like a stadium.

Not Aleppo pine ... HUGE, messy and tend to fall over in wind storms.

Desert willow, Pistachio, even a Mesquite would do better back there. Any of them can reach 20 feet in a couple of years with only modest supplemental watering.

3x a week is too much ... you need to water less often, and deeper for a lawn. That will also help the Jacaranda.

http://ag.arizona.edu/azmet/phx/ explains how to check your sprinkler output and you just keep checking to see how much water (sprinkler time) to give the lawns. If you do it now, the lawns will never know they've been put on a diet.