Download June 10, 2013

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Lorraine P. Berkett
June 10, 2013
Quick Update -Fire Blight -- Excellent article on scouting for blossom blight symptoms on web from MSU.
Mark Longstroth of Michigan State University Extension has written an excellent article entitled:
“Scouting for Blossom Blight Symptoms of Fire Blight in Apples.” It includes explicit pictures of
the symptoms for which one should look. The article is below; it was posted on the web on June
5, 2013 at:
http://msue.anr.msu.edu/news/scouting_for_blossom_blight_symptoms_of_fire_blight_in_apples?utm_source=Fruit
+Production+-+MSU+Extension+News+-+6-7-13&utm_campaign=Fruit+6-7-13&utm_medium=email
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“Scouting for blossom blight symptoms of fire blight in apples”
Scouting for blossom blight symptoms allows you to gauge how effective your protection was
during bloom. This article describes the blossom blight or spur blight phase of fire blight with
pictures taken in southwest Michigan.
Posted on June 5, 2013 by Mark Longstroth, Michigan State University Extension
Fire blight is a serious bacterial disease of apples and pears. Fire blight attacks all tissues of apple trees:
blossoms, leaves, shoots, branches, fruits and roots. The bacterial pathogen Erwinia amylovora that causes
fire blight is harmless to humans. The bacteria usually enter the tree through flowers during bloom. Under
rainy conditions, the bacteria then move into the tissues of the flower and the rest of the flower cluster.
This infection causes the death of the flowering spur, which is often the first visible symptom of the
disease.
Once established in the tree, fire blight quickly spreads from the current season’s growth into older growth.
Death of infected branches is rapid and the leaves do not have time to fall off the tree. Young, non-bearing
and newly bearing trees can easily be killed by the infection while mature-bearing trees usually survive
even if all the new growth is killed.
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Photo 1. Wet apple blossoms. Rain during bloom can be a disaster.
Photo credit: Mark Longstroth, MSU Extension
Fire blight blossom infection
Blossom infections are initiated by bacteria carried to open blossoms during bloom by bees and other
insects. The bacteria thrive on the stigma of open blossoms where pollen lands to pollinate the flower.
With warm temperatures, bacterial numbers can quickly rise to incredibly high numbers on the nutrient
rich exudates of the stigma, but do no harm there.
Rain during warm weather during bloom can cause infection (Photo 1). Rain washes the bacteria down off
the stigma to the base of the flower. At the base of the flower are nectar pores where the bacteria can
enter the plant. Once in the plant, if the conditions are warm, the bacteria begin growing and kill the plant
tissues. Disease symptoms are not readily apparent since the disease needs warm conditions and time
before symptoms develop. Often the first flowers to bloom out are not infected even when the conditions
are hot and wet because the flowers were not inoculated with the bacteria. The bacteria are spread from
flower to flower by bees and other insects.
Blossom blight symptoms
Often the initial fire blight symptom seen in an orchard, blossom blight usually indicates where the
pathogen first gains entry into the tree. The bacteria kill the flower (blossom blight) and often the spur
(spur blight). The damage may resemble frost injury to fruit spurs.
Photo 2. One flower in this cluster was infected with the fire
blight bacteria. Photo credit: Mark Longstroth, MSU Extension
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Blossom blight symptoms are hard to see unless you are actively inspecting the bloom for fire blight
symptoms or assessing fruit drop to make thinning decisions. Affected tissues first have a water-soaked
appearance that quickly turns black or brown. The bacteria then moves out of the infected blossom cluster
and symptoms of necrotic (dead, brown or black) tissue can be seen in nearby leaves and fruit. These
symptoms appear where the petiole joins the leaf or fruit.
The time of appearance of the symptoms depends on the temperature after infection. The warmer the
temperature, the sooner symptoms appear. In Photo 2, you can see not only the infected fruitlet, but leaf
symptoms on some of the spur leaves as the bacteria have begun to move out of the fruit. The first leaf
symptom is dying tissue where the petiole or leaf stem meets the leaf blade.
Photo 3. This fire blight infection has spread from one cluster to
other shoots and leaves. Photo credit: Mark Longstroth, MSU Extension
Spur blight symptoms
Spur blight is the collapse of entire spurs after the initial fire blight blossom blight symptoms on single
flowers, the bacteria begins to move inside the plant, killing nearby tissues. Photo 3 shows spreading fire
blight where nearby tissues are collapsing as the bacteria moves into healthy spurs and shoots.
Photo 4 shows several symptoms of fire blight. The flowers on the right were infected and you can see the
black stems of the flowers. The bacteria have spread into the tree and infected the shoot on the opposite
side of the branch. The systemically infected shoot has orange-colored leaves at the tip and is starting to
wilt. You can also see wilting leaves around the infection and the woody stem is also starting to ooze, both
above and below the initial infection.
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Photos 4 and 5. Left, Flowers on the cluster on the right were the first infected and the infection has
spread to the shoot on the right. Right, Older spur blight symptoms. Photo credits: Mark Longstroth,
MSU Extension
The accompanying picture (Photo 5) was taken several weeks after the onset of symptoms. On this tree the
infection has killed several spurs and caused oozing at the base of the spurs. This canker has not moved far,
but has the potential to girdle the limb and kill the shoot. If this canker remains active it will spread fire
blight in this orchard next year.
Photos 6 and 7. Left, Fire blight leaf symptoms. Right, Initial fire blight symptoms in shoot tip.
Photo credits: Mark Longstroth, MSU Extension
Photo 6 shows the dead tissue in the midrib of the leaves on and near an active infection indicates that the
bacteria are moving through the stem and have now moved into this leaf. Photo 7 shows the orange or
yellow shoot tips are often the first sign that a shoot is infected systemically and will die. The color
indicates that the bacteria have arrived at the shot tip. The entire shoot will quickly wilt and die.
For more information from Michigan State University Extension, see these articles:
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Watch video on fire blight shoot blight development from George Sundin’s lab.
When to prune out fire blight: To prune or not to prune
New video resources in tree fruit pathology from MSU
Prune out fire blight in the winter
Summer pruning apples
This article was published by Michigan State University Extension.
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Thank you Mark for writing this very informative article !
Also see Mark’s article listed above on “When to prune out fire blight: To prune or not to prune”.
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”New” Insect Pest found in OrganicA Orchard - Ann Hazelrigg who is conducting research in
Orchard 1 found the larva pictured below boring in new shoot growth. She sent a specimen off to
Dr. Alan Eaton at UNH who identified the larva as that of the Pith Moth.
Pith moth larva from Orchard 1.
Dr. Eaton has written a fact sheet on “Borers in New Hampshire Apple Trees” which contained
the following information about the Pith Moth and which can be found at:
http://extension.unh.edu/resources/files/Resource001830_Rep2590.pdf
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IMPORTANT: It is the grower’s responsibility to ensure that any crop production practice or material used in the
orchard is acceptable in their particular state’s organic certification program. Some materials deemed organically
acceptable on the National List may not be acceptable in some states. Contact your federally accredited certifying
agency to know what is acceptable and to ensure compliance with regulations in your state.
Where trade names or commercial products are used for identification, no discrimination is intended and no
endorsement is implied. Always read the label before using any pesticide. The label is the legal document for the
product use. Disregard any information in this document if it is in conflict with the label.
We Value Your Input and Want to Address Your Needs
Please send your comments and suggestions to [email protected]
For more information on the OrganicA Project please see:
http://www.uvm.edu/organica/
The OrganicA Project is being funded by a grant from the
USDA Integrated Organic Program and by other funding sources.
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