[NAFEX] Pears/Fireblight

Douglas Woodard dwoodard at becon.org
Sun Jul 5 15:23:32 EDT 2009

The level of available nitrogen has a very large effect on a pear tree's 
susceptibility to fireblight.

About 1986 I saw some old trees of Sheldon which had been partly 
topworked to Bosc and fertlized with nitrogen to promote growth; the 
Sheldon branches became heavily infected with fireblight although they 
had been apparently not significantly bothered by it before.

In 1983 I saw a small block of young Bartlett trees infected with 
fireblight; the grower said for the first time. He attributed it to his 
having planted a patch of sweet corn across a farm track from the 
Bartletts, and having fertlized the sweet corn with nitrogen.

The same grower told me that some years prevously the Geneva station had 
published recommendations on mineral nutrition to minimize fireblight. 
I've forgotten most of what he said about it but my recollection is that 
calcium and magnesium were important.

I've been told that a major reason for the Agriculture Canada program to 
breed fireblight resistant pears at Harrow, Ontario, was to allow 
growers to fertlize with nitrogen and increase yield and fruit size; 
although I understand that the region around Harrow also typically has a 
worse fireblight problem than the Niagara Peninsula, which is itself bad 

Doug Woodard
St. Catharines, Ontario, Canada

Anton Callaway wrote:
> I've wondered about the possibility of there being multiple strains of Erwinia amylovora.  For instance, Ethan has reported that 'Spalding' in Houston blights badly, but here it's almost completely blight-free.  I recognize that Houston may be one of the few places in the country that are hotter & about as humid as here in piedmont NC.  However, I also considered the possibility that his neighborhood was inhabited by a more virulent bacterial strain.
> That is why I was so interested in Dr. Richard Bell's answer to this question at the NAFEX meeting in Lexington a few years ago.  He stated that there weren't any known strains of significantly differing virulence.  If that's true, then environment becomes the biggest determinant in susceptibility of a specific pear cultivar.  With some exceptions to prove the rule, there is a blight gradient that worsens as you go south (in the humid Eastern U.S.).  For instance, 'Honeysweet' and 'Megietsu' blight badly here, but are reported to be quite resistant in the Mid-West.
> 'Magness' is known to be blight-susceptible in trunk, but resistant in leaves and flowers.  So, like you've observed, it doesn't wall off infections well when they enter the larger limbs (hail is the classic injury that inoculates trunks).  'Magness' will produce well here for 10-20 years, but invariably will blight out in an epiphytotic accompanied by hail. [BTW, my spellchecker suggests, "Madness" for the word, "Magness".  Hmmm.]
> Anton
> -----Original Message-----
>> From: fuwa fuwa usagi <fuwafuwausagi at muchomail.com>
>> Sent: Jul 3, 2009 7:50 PM
>> To: nafex at lists.ibiblio.org
>> Subject: [NAFEX] Pears/Fireblight
>> It was written:
>> The data on fireblight susceptibility of 'Wilder Early' are mixed.  I 
>> rather expected my trees to perish quickly when I first grafted them. 
>> My reply:
>> You might want to consider that fireblight is not a problem rather a series of problems.  Or stated differently it is very likely there are strains of fireblight.
>> In my area this infamous Magness does not successfully wall of fireblight, it consumes the tree.  On the other hand Harrow Sweet, Harvest Queen, and Potomac for wall off fireblight when it occurs.  Every Magness in my yard had been lost to fireblight unless it was  branch graft on another tree, i.e I get  a few Magness from my Harvest Queen.
>> On the other hand plain ol' Bartlett does fine here.  So do many blight susceptible trees. 
>> tfb

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