[NAFEX] Fire blight on dwarf apple espalier

dwoodard at becon.org dwoodard at becon.org
Wed May 30 05:44:13 EDT 2007


And for the future, during the growing season infection is readily
trnsmitted on cutting tools. Tools need to be disinfected after each cut.
I believe a chlorine bleach solution is usually used, I don't know whether
alcohol is effective.

Two inches is far too small a margin. I think the usual practice is eight
inches below visible discolouration. However you should get instructions
from  a *knowledegable source* (state or provincial government?) and
follow them.

Fireblight has to be dealt with ruthlessly and meticulously.

Avoid heavy nitrogen ferrtilization, especially with pears. With
nonresistent pears you may want to avoid *any* nitrogen fertilization. I
have seen a young block of Bartlett pears infected because a field across
a laneway was planted to sweetcorn and the pear roots running under the
laneway picked up the nitrogen fertilizer from the sweetcorn field.

I've also seen several old trees of Sheldon pear ruined by fireblight
after they were topworked to Bosc and fertilized with nitrogen.

I understand that the Harrow program of breeding fireblight resistant
pears was started to a large extent to be able to fertilize with nitrogen
and get economic yields.

Doug Woodard
St. Catharines, Ontario, Canada


> Betsy,
>
> If any tree has blight on the trunk ( sometimes cankers can be seen on the
> trunk or stems leading to the trunk) you will need to remove the tree or
> trees.  With no protection (copper or streptomycin) the other trees will
> become infected and you could lose all of your trees in a very short
> period
> of time.  You will need to spray the remaining trees since you have
> inoculum
> in your orchard already.  Here are now the six symptoms of fire blight:
>
> Six Symptoms of Fire Blight
>
> Blossom Blight
>
> Blossom blight is usually the first symptom visible in the growing season.
> Flowers will first appear water soaked ("soggy") then will shrivel and
> turn
> dark brown or black in color. Some flowers may fall but typically they
> remain attached to the spur shoot. Bacterial ooze may also be produced and
> be visible on the flower stalk.
>
> Shoot Blight
>
> Shoot blight symptoms are easy to recognize and allow one to distinguish
> fire blight from other diseases of this group of plants. The most common
> symptom is necrotic young shoots that appear "scorched". It is this
> symptom
> that gives the disease its common name, fire blight. Young stems will curl
> at the tips revealing another classical symptom, "shepherd's crook".
>
> Leaf Blight
>
> Typically leaf blight results from secondary infection. The pathogen may
> enter directly through naturally openings in the leaf or through wounds
> caused by hail, strong winds, or insects. Necrotic areas may appear,
> however
> darkening of the midrib and petiole is very characteristic.
>
> Fruit Blight
>
> Like leaves, immature fruit can become infected through natural openings
> and
> small wounds.  Sections of the fruit will initially appear water soaked
> and
> ultimately turn brown to black.  Blighted fruits will typically remain on
> the plant and a milky to amber-colored ooze may appear on the fruit
> surface.
>
> Limb and Trunk Blight
>
> On more susceptible varieties, infection will spread into older limbs and
> the truck where cankers can develop. The cankers will appear as a sunken,
> darkened area with the bark peeling back. It is here in the cankers where
> the bacterial cells overwinter. As the temperature increases in the
> spring,
> bacterial cells become active and the sticky ooze begins to flow out of
> the
> cankers attracting insect vectors.
>
> Rootstock Blight
>
> Yet another phase of fire blight, rootstock blight has been recognized
> recently and is associated primarily with the highly susceptible M.26, M.9
> and Mark rootstocks. On these trees, just a few blossom or shoot
> infections
> on the scion cultivar can supply bacteria that then move systemically into
> the rootstock where a canker often, but not always, develops and
> eventually
> girdles the tree. Trees affected by rootstock blight generally show
> symptoms
> of decline and early death by mid to late season, but may not be apparent
> until the following spring.
>
> There are several sprays that you can use for fire blight and 2 of those
> are
> considered organic:  Copper and Streptomycin in the form of Agri-Mycin or
> Agri-Strep.  The copper sprays have to be done at dormancy or just prior
> to
> bud break.  Did you do a dormant copper spray or a strep spray at bloom?
> If
> not, your best option is to do a strep spray NOW.  Agri-Strep should be
> available at your local nursery or garden store.  Even though you are past
> petal fall and are probably at 4th or 5th cover, you can still do a strep
> spray as if it were a "trauma" spray.
>
> Trauma blight situations occur with high winds and hail, and these events
> can still cause devastation to orchards. Trauma blight situations should
> still be managed with applications of streptomycin, as
>  streptomycin is the best material to use and will give the best
> management
> of fire blight in a post-trauma blight situation where resistance is not
> an
> issue.  Since you may have never used strep before, resistance would not
> be
> an issue for you.  The strep spray is typically done at full bloom, but
> can
> be done later as with "trauma" blight.  Even though we did our strep spray
> at full bloom, we still have incidence of shoot blight, twig blight and
> root
> blight in our orchard.  Tonight we are doing a Nova 40W/Dithane DT
> (mancozeb) spray because we cannot do another strep spray this season for
> fear of resistance buildup.
>
> I am going to refer you to the West Virginia University site
> (http://www.caf.wvu.edu/kearneysville/disease_descriptions/omblight.html)
> for a good overview and photos for fire blight.  I hope this helps!
>
> Dennis Norton
> Royal Oak Farm Orchard
> http://www.royaloakfarmorchard.com
> http://www.theorchardkeeper.blogspot.com
> http://www.revivalhymn.com
>
>
> ----- Original Message -----
> From: <Hilborn.E at epamail.epa.gov>
> To: "North American Fruit Explorers" <nafex at lists.ibiblio.org>
> Sent: Tuesday, May 29, 2007 11:17 AM
> Subject: [NAFEX] Fire blight on dwarf apple espalier
>
>
>>I am a newbie apple grower and need some help.
>>
>> I am growing dwarf apples (on M9 root stock) in an oblique cordon
>> espalier, 2 foot spacing. I tend to garden organically.
>>
>> I have had minimal problems with fire blight in previous years, light
>> pruning was all that was needed.
>>
>> Now my 4 year old American Golden Russet is severely affected.
>>
>> I have had to prune repeatedly this spring to remove affected wood (and
>> 2 inches below damage if possible). However,  multiple lower laterals
>> have been removed back to the main trunk on this tree, and I can see
>> brown cambium at the cut, so I believe that it is infected back to the
>> trunk.  A few other trees in the collection appear to be only lightly
>> affected.
>>
>> Question: Given the spacing and pruning intensity on my small collection
>> of 24 apples and pears grown in this manner, is it best for me to remove
>> this tree to save the others, or is there a way to successfully treat
>> it?
>>
>> Do I need to spray antibiotic over all the trees?  Is it commercially
>> available?
>>
>> Betsy Hilborn
>> NC 7a
>>
>>
>>
>
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