One of my 6 Eumundi quandongs has started to look really unwell all of a sudden. I only watered it once this winter (only a light water) but the leaves are gradually starting to curl up and die from the top down. The soil does feel a little moist, but no sign of any pests, mites or other obvious symptoms. Only planted 1yr ago, fertilised every 4-5months with seasol but has been declining rapidly over the past 2wks. Any ideas?
Your sick tree looks like it is suffering from lack of water. However, as the one next to it is looking great I think the problem may be connected to roots. The roots may be been damaged when the tree was planted, being eaten by soil pests ie Curl grubs or be malformed due to poor propagating practices at the nursery (roots may be circling and not spreading outwards). The only way to really tell is to carefully dig up the plant and examine the roots and the surrounding soil. If the roots are circling the tree will always be sickly and not reach its full height, you best option would be to replace the plant.