HORTICULTURE

Blossom Blight Symptoms

Mark Longstroth

This page is a description blossom bight or Spur blight phase of fireblight disease in apples illustrated with pictures I have taken of the disease here in Southwest Michigan.

The bacterial pathogen Erwinia amylovora that causes fire blight is harmless to humans. Fire blight attacks all the tissues of the tree; blossoms, leaves, shoots, branches, fruits, and roots. The disease bacteria usually enters the tree through flowers during bloom. The bacteria then moves into the tissues of the flower and down into the other thissues of the flower cluster. This causes the death of the flowering spur. Once established in the tree fire blight quickly invades through the current season's growth into older growth. Death of infected branches is so rapid that 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.

Blossom Blight

Blossom Infection
The bacteria thrives on the stigma of open blossoms during bloom. With warm temperatures bacterial numbers can quickly rise to incredibly high numbers. Rain during or after warm weather during bloom can cause infection. 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 and begin growing. Disease symptoms are not readily apparent, the disease needs some time and warmth before symptoms develop. Often the first flowers out are not infected even when the conditions are hot and wet because the flowers have not been inoculated with the bacteria. The bacteria is spread from flower to flower by bees and other insects.

Blossom Blight Symptoms
Often the initial fireblight symptom seen after bloom, spur blight is caused by the bacteria entering the flowers during bloom when rain washes the bacteria down into the base of the flower were it can enter through the nectar pores into the plant itself.  The bacteria kills the flower (blossom blight) and often the spur (spur blight).
The first symptom a grower can see is blossom blight, the collapse of the young fruitlets after bloom. This symptom is hard to see unless you are actively inspecting the bloom for fireblight 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 begin to move out of the infected blossom cluster and initial 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 will appear. In the picture to the left you can see not only the infected fruitlet but leaf symptoms on some of the spur leaves as the bacteria has begun to move out of the fruit. The first leaf symptom is dying tissue where the petiole or leaf stem meets the leaf blade.

Spur Blight, collapse of entire spurs

After the initial spur blight symptoms,  the bacteria begins to move inside the plant killing nearby tissues. The picture above shows spreading fire blight where nearby tissues are collapsing as the bacteria moves into healthy spurs and shoots.  The photo on the right shows several symptoms of fireblight.  The flowers on the right were infected and in the larger linked picture you can see the black stems of the flowers. The bacteria has spread into the tree and the spur on the opposite side of the branch. the systemicall infected spur has orange colored leaves at the tip and is starting to wilt.  You can also see wilting leaves around the infection. the woody stem is also starting to ooze, both above and below the initial infection.

Older spur blight, later in the season

This is a picture 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.  But the canker has not moved far.  These cankers has the potential to girdle the limb and cause the shoot to die. If this canker remains active it will spread fireblight in this orchard next year.

Fire blight leaf symptoms
Dead tissue in the midrib of the leaves on and near the spur indicate that the bacteria is moving through the stem.
Another common symptoms can be seen in the photos above where the leaf tissue quickly turns black.

Orange Shoot Tips
Orange or yellow shoot tips are often the first sign that the shoot is infected systemically and will die.

Back to the Fire Blight Symptoms Page.

Back to the Fire blight Links Page

For more information see the Fireblight Articles at the University of West Virginia.

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First Posted: May 25, 2002
Last Modified: May 25, 2004