Question
I am getting a whitening of leaves on the yuccas.  It is summer at the moment with plenty of rain had in the last few months and once it has stopped raining the weather has been quite hot....do you have any ideas?

Answer
If the plants are newly planted in the landscape I would say it sounds like sunburn or sunscald.  Look at the leaves closely and see if you see little white to yellow flecks in the leaves.  This may be a sign of potassium deficiency.  Other than these two suggestions I cannot think of anything else.  Yuccas are usually carefree plants.  If you see something else upon close inspection, respond back with your observations and I will try to address the issue.  Good Luck.