Not a disease.

Newly planted trees often need to be watered every day or two. And the *critical* place to apply the water is directly into the rootball.

I'll disagree slightly with jean, the 'disease' is lack of water.

Dan

frogribbit, did you fertilize when planting or after? I have seen a similar look (dead tan tip, darker brown line between the green and tan areas) when new plants have been fed before they have had time to establish a good root system. But, could be too little water as well.
hortster

We have clay soil - I'd think watering every day (or even two) would be too much??

Horster - I did fertilize once with half strength Miracle grow. So do you think I 'burned' the root ball?