That's a LOT of watering for mesquites. If that tree is in an area that drains poorly, you might be drowning it. Then it looks stressed and loses leaves so you water more ...

I'd stop watering them all as soon as the monsoons start. Remove the emitters reduce the deep watering to once a month. Next year, maybe one thorough soaking in May and one in June.

Welcome to the world of mesquite. They are such messy trees and drop things most of the year, especially summer.

We agree with lazy_gardens. It sounds like an awful lot of water for Mesquite trees. These are arid plants and like to dry out completely before each watering. May want to take them off the regular drip line and just hit them with the deep watering once a week right now. That should be plenty for established trees.

One reason you may be seeing this with only one tree could also be that area is heavy in caliche which isn't allowing for drainage and your other trees may have better draining soil around them. Out here it is crazy, but you can have pockets of clay soil just feet away from good draining soil.

If you have more questions on watering and care for desert trees you can check out our website, we have some good care guides and information and here is the link to our established care guide for desert trees ( https://www.moonvalleynurseries.com/tree-care/watering-basics ), this should help too!