According to hardiness zone classifications, mountain laurel, golden rain tree, tulip tree, sweet gum, and liriope are recommended landscape plants for Louisiana. They are recommended in heat zone 8 - so you can see that probably the least amount of stress on these plants may send them into decline when they are being grown in Louisiana even though they have been considered reliable plants as long as hardiness zone recommendations were considered. Heat is no doubt one of the major limiting factors to successful plant growth during the summer months in Louisiana. Many people have suggested that a relative humidity zone map is the next step in categorizing plants. This is a good idea.
Humidity influences transpiration and the ability of a plant to cool itself.
Also, more humidity increases disease problems. We potentially have more disease problems in south Louisiana than north Louisiana due to the significant changes in relative humidity. Water availability or limiting water stress goes a long way in eliminating plant stress. Maintaining optimal soil moisture levels is critical. It is hard to do without proper irrigation management.