Hello Ann,

Thank you for reaching out to Ask a Gardener, Colorado State Extension office about your Red Delicious apple tree.  There are several reasons why the leaves might be "cupping" or curling.  The photo shows no evidence of fireblight or mildew, however mildew cannot be ruled out.  

Here are some common causes of leaf curl:

• Transplant shock. (Common when planting on a hot, sunny day, or late in the season.)
• Not enough water or too much water. (Roots need oxygen.)
• Fertilizer. (They’re salts, and can draw water away from roots, “burning” the leaves. Avoid fertilizer in the first season.)
• Too much manure or compost in the planting hole. (Same as above.)
• Planting too shallow or too deep. (Holes should be wide but not too deep. Keep the root flare and graft above the soil line.)
• Phototoxicity from water or sprays on the leaves during hot, sunny days.
• Fungal diseases like apple scab. 
• Apple borers in the trunk. (Common pest in home orchards.)
• Vole damage on trunk.
• Planting on ledge. (Ledge limits root growth and can heat roots.)

Thank you, I hope you find this information helpful. 

Erin D.

Colorado Master Gardener