New Dogwood - leaves turning brown
I live in the Detroit area. I just planted a 7' flowering Dogwood (Cornus Florida 'Cherokee Brave') less than 2 weeks ago (mid July). I purchased it at English Gardens, it was in a plastic pot. I have good light sandy soil, and I added peat when planting. I also used root starter liquid fertilizer (diluted w/water). I followed planting instructions well. I have been watering it religiously - trickling with hose for at least an hour twice a week, plus using sprinkler, and testing soil with my finger. It is is in full sun, and it has been extremely hot - 90-100 degrees everyday last week.
Problem: Within a couple days of planting the leaf tips started turning brown. Then a patch of leaves started turning purple (their autumn color I believe). Little by little more leaves are getting brown tips, then the margins turn brown and crumbly. Some leaves have holes/cracks down the center. Some have turned completely brown and fallen off.
Does anyone have suggestions on what is happening and what I should do? I called the MSU hort.hotline and they said it could be transplant shock or effects from the high heat (many plants are suffering right now). They are also sending me some info on anthracnose. I'm hoping that my brand new tree does not have a fungus.
Any and all suggestions are welcome! Thanks in advance!