North American Fruit Explorers mailing list at ibiblio

["Mark & Helen Angermayer" <hangermayer@isp.com>]

Hi Steve,

My experience with apple scab is mostly from reading, but what you describe
seems to match up quite well with the literature.  Scab infections start
with "primary" infections that result from last years leaf litter, fruit
drops, and infected twigs.  The scab fungus waits till the spring to release
the primary spores.  Interestingly, the fungus waits till a good wet period
to release its spores, then it's pretty much done.  In other words, the leaf
litter is like a roman candle.  Once it's shot, it's done.  So if you can
protect your apples from the primary infection (if I recall from the period
from tight cluster to first cover) then there is no more inoculum left to
infect your apples.  However, if the current season's crop gets infected,
the infected apples on the tree will continue to release spores all summer
long and it becomes a constant battle to keep scab from spreading.  It also
means you'll have more primary inoculum for next year.  So your early
fungicide treatments probably were protecting you from scab in past years.

No idea why Manzate has such a lengthy withdrawal time.  As you suggest, it
doesn't have any systemic action and is considered a protectant fungicide
with about 24 hours kickback activity.  Maybe it's a real 'sticky' fungicide
that just takes a long time to wash all the residue off.

Mark
KS
----- Original Message ----- 
From: "Steve" <>
To: "NAFEx" <nafex@lists.ibiblio.org>
Sent: Tuesday, July 15, 2008 10:28 PM
Subject: [NAFEX] Apple Fungicide


> We had a stretch of damp weather and I have quite a bit of scab on my
> apples this year. I had nice crops of apples the last 2 seasons with
> absolutely no scab. What was the difference? Maybe it was the weather
> but maybe not:
>
> Three or four years ago, I bought some Manzate. I actually bought it
> with my other hobby in mind; I wanted to cure some problems on my orchid
> plants that I assumed were fungal in nature. That didn't work out as I
> hoped, so I read the label to see what fruit or garden plants I could
> use it on. Pome fruits were listed so I used it on my apple trees. It
> was labeled for use no later than 77 days before harvest. (I couldn't
> help but wonder how they arrived at that exact number of days.) The last
> 2 seasons, I did two sprays (I think, ... it may have been only one
> spray last year) before and/or toward the end of bloom. (My earliest
> apples probably were ready in slightly less than 77 days after the last
> spray.)
>
> As I said, my apples were completely clean those 2 years. This year I
> didn't use the Manzate and, even though I plucked off the worst of them
> at my last thinning, I'm going to have a lot of blemished apples. This
> is the only fungicide I have ever used on my apple trees. My question
> is, is the Manzate so effective that it prevented scab right through the
> entire season with no more than 2 early sprays, or was it really the
> weather that made all the difference?
>
> One other thing. I wondered if Manzate was somewhat systemic and that
> was the reason for the long 77 day requirement before harvest. This site
> was shown by someone here a month or 2 ago:
> http://www.ipm.osu.edu/fruit/03icm31.htm\
> The third section down discusses the effects of rain on fungicides. Some
> are listed as penetrating the leaves and fruit tissues and don't wash
> off. Manzate is in the group that does wash off in the rain, making me
> wonder why the 77 day preharvest requirement and making me seriously
> question if the Manzate was really what saved my apples the last 2 years.
>
> Steve in the Adirondacks (Zone 4 on the map, zone 3 by the thermometer.)
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