Question
Two of my 3yr old holly trees are starting to lose color (now a lighter green ) and some leaves are looking wilted. It has been very hot in KC, near 100 for a week or two. Two of the three trees, all of which are about 7' tall, have the lighter color and wilted leaves but the middle one looks just fine.
Is it a disease or dryness or something else.?
Thanksk

Answer
Hi Brenda,

Given the high temperatures, it is quite likely that the problem is related to the heat.  If you are not watering the trees, you should start.  It is important that the trees receive ample water to help them withstand the temperature extremes.  You should water the trees deeply at least 1-2 times each week if you are not receiving adequate rainfall.  This means that you want to water the trees slowly so that the water can penetrate to the deeper roots and not just wet the surface.  You may want to use a low flow rate on your sprinkler so water comes out more slowly, use a soaker hose around the base of the trees or put your hose on low and move it every 5 minutes or so to different areas of the root zone.

Trees vary in how the respond to temperature.  The one in the middle may be more protected from the scorching sun and drying winds than the trees on the edges.  For this reason, the damage will not be as severe.

It is unlikely that your problem is due to a disease at this time.  Most pathogens are not active at 100F and for those that are active, they have a heavy moisture requirement.  Based on your description, I think a disease is unlikely.  

Let's hope for cooler temperatures.  I'm in Oklahoma and our hollies are doing the same thing!