Subject: Re: [NAFEX] Necrotic leaf
blotch? - now apple scab
Dennis,
I agree with your assessment...just typical apple
scab, nothing as unconventional as Necrotic leaf blotch. I didn't
know that scab could cause yellowing of the leaves, but now I know.
All the apples on the tree were bagged in plastic one
week before the scab symptoms appeared, so it will be a good test to see if
the bags successfully stopped the apples from getting damaged.
I am trying to stay organic on my trees, so I'll try
micronized sulfur for control. I guess I could use copper as well, since I
would guess the bagging should prevent the russeting that can occur with the
application of copper sulfate.
Thanks for your help!
Nate
Dennis Norton
<dmnorton@royaloakfarmorchard.com> wrote:
Nathan,
The leaf in the photo is probably apple scab
and from the description you gave of the weather, the temps were right for
an infection period during the 90+ temps over Memorial Day. Our scab
software models here at Royal Oak Farm also showed an infection period for
the same time, which is our third infection period in the last 2
weeks. Nova or Captan is the necessary spray, but the timing is
critical. If you only have a few trees, Bonide Fruit Tree Spray
contains Captan (needs to be sprayed within 72 hours of an infection
period to really work), or go to http://www.planetnatural.com/site/xdpy/kb/apple-scab.html.
Refer to http://www.extension.iastate.edu/Publications/PM1282.pdf for
the use of any sprays. Hope this helps
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.
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