Q.Huckleberry tree turning yellow
We live in Chicago. We have a huckleberry tree that has been doing great over the years. It is now losing leaves, turning yellow and looking droopy. Are we watering it too much? Too little? Is it a fungus? What else?

Excess watering can cause yellowing leaves, if the roots sit in soggy soil, the plants can suffer root rot. Leaves would turn brown and plants can die off.
Make sure the soil is draining.
More serious causes of yellowing leaves could be herbicide injury or Botrytis Stem or Leaf Blight.
The links below will help you determine the cause of the plant yellowing.
http://www.fruit.cornell.edu/berrytool/blueberry/leaves/BBleafbrowning.htm
https://www.gardeningknowhow.com/edible/fruits/huckleberries/huckleberry-plant-care.htm
https://www.gardeningknowhow.com/plant-problems/environmental/plant-leaves-turn-yellow.htm