It appears to fit the description of nectrotic leaf blotch, as the Twin Cities had one cool overcast week in the 60's followed by 3 hot and humid days (90+ degrees) over the Memorial Day Weekend. I'm not sure if Zestar is a Golden Delicious relative (Official cross is State Fair x MN 1691), which seems to be a prereq for this type of leaf blotch . Anyone else seen this on Zestars?
I'm tempted to just leave the tree alone...I have
never sprayed my trees for anything and really don't want to start if possible. Has anyone dealt with this problem before? Will I lose my crop/tree if I ignore it?
Thanks,
Nate Torgerson
Andover, MN zone 4a
Description courtesy of Tennessee Extension services (there is also a picture on the site):
Necrotic leaf blotch is actually not a disease, but a physiological disorder. It occurs on Golden Delicious and its sports. The affliction often occurs in waves during the summer. It tends to be more severe when hot, sunny weather follows several days of mild, cloudy weather. Large, irregular-shaped, necrotic (brown) spots appear suddenly on green leaves. Most affected leaves soon turn yellow and fall from the tree.
Defoliation can be significant. Although necrotic leaf blotch is not caused by a fungus, severity is decreased by a regular fungicide program.