[NAFEX] Fire blight on dwarf apple espalier

dmnorton at royaloakfarmorchard.com dmnorton at royaloakfarmorchard.com
Tue May 29 23:49:39 EDT 2007


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 
for a good overview and photos for fire blight.  I hope this helps!

Dennis Norton
Royal Oak Farm Orchard

----- 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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