We went away for four days and when we came back our tangerine tree was brown and withering, with the fruit and leaves dried up. We've been watering for at least 10 days and see no sign of improvement. It appears as though the tree is dying. Is there anything that we can do to save it, or what else can we do to maintain its health, if it's still alive?
If the tree was newly planted, it likely went into shock or something could be constricting the roots from taking up water. A fungus could also have affected your tree. You may be able to check if the tree is still alive by scraping the bark. If it's still green and the branches still pliable (able to bend without snapping off), then your tree is still alive. Treating it with neem oil and watering the tree when the soil becomes dry should help. Also, gently tamp down the soil when watering to collapse any possible air pockets. You may need to check the roots as well to see if there is a problem, such as rot. Here is more information on that: https://www.gardeningknowhow.com/plant-problems/disease/root-rot-in-garden-plants.htm