could be quite normal - if its close to a sprinkler, is there a chance that the sprinkler has been on when the sun is on the plant? This might scorch the leaves and cause withering, or it might just be that the heat was too much. Otherwise, though ,inspect the leaves, stems branches and trunk thoroughly for signs of infestation or disease.

If it is one or a few specific branches where the leaves are withering, it might be Verticillium wilt. I hope it isn't, there's no real cure for that.

As T says, very likely Verticilium wilt. They are prone. Cut out the stem with the withered leaves, and hope it dosn't spread. When you've cut off the stem, have a look at the cut end. If it is fungal (verticilim wilt), there will be dark rings obvious in the tissue. Phil J

Thanks; I will see if it is verticillium wilt; hope not!

I hope not too - that's what I thought initially, but didn't want to say - still worth looking for other, less damaging causes.