Fruitful Land

Fireblight  (Erwinia amylovora) is a potentially serious bacterial disease that kills the living tissue in the bark. It invades the Apple tree through blossoms or through the tender new growth of shoots. The potential for Fireblight infection is determined to a large extent by the weather conditions, the variety, and the vigor of the tree.

Fireblight infections  initiate through the flower pistil, young actively growing shoots, or cuts in leaves and tender bark usually torn open by a hail storm.

Conditions for severe infections can develop suddenly so it is advisable to be vigilent during bloom and the first few weeks following bloom. even though the bacteria can infect blossoms, fruit, shoots, stems and leaves the two most common infections are Shoot Blight and Blossom Blight. Once the bacteria gets inside the tree it will move down the tree from the initial site toward the trunk. Severe infections can kill the tree ,but I have seen trees recover from some rather devestating attacks.

BLOSSOM BLIGHT can occur any time that the flowers have developed enough to expose the pistil.The pistil gives a direct path to the inside of the plant, once the bacteria is in the plant it is hard to stop, Infected flowers look water soaked and then turn dark brown. Heavily infected tress looked scorched, heb=nce the name, fireblight.

SHOOT BLIGHT is the most easily seen symptom. It can occur  anytime there are warm humid conditions and there is the shoots are actively growing. Hail and high winds can tear the tissue and dreate thousands of new infection sites. Infected stems will exude a milky ooze that contain millions of bacterial spores. Shoot tips and leaves turn brown and develop a characteristic "shepherd's crook", a sure sign of infection. The dead leaves cling to the stem after death.

FRUIT BLIGHT Infected fruit exudes  the same sticky ooze as the stems. The fruits stop growing, turn brownish and fall prematurely.

If a tree is severly infected, thunderstorms and warm rains will wash the baterial ooze throughout the tree and the disease spreads easily.

CONTROL: The best time to control fireblight is in the winter. Cankers formed at the lowest part of the infection shouold be pruned out. Be sure to cut 12-18" below the visible canker. Fireblight bacteria are present in the tissue before the limb shows any symptoms. Even though the bacteris is dormant in the winter, you can still spread ti disease from limb to limb with your loppers. I do not reccommend pruning out infected shoots during warm weather AT ALL. Even when we disinfected our pruning tools between every cut, we always do more damage than good when we attempt to cut out the limb infections during the summer.

In Minnesota, we recommend copper sprays at late dormancy (early spring before bud break).This is especially important of you had fireblight during the previous season. Copper can be toxic to leaves and flowers, but it will kill any live bacteria it contacts in the overwintering cankers. Copper will also kill any apple scab that it contacts on the overwintering leaf litter.

Severe pruning can set up a tree to be prone to infection as this promotes overly vigorous shoot growth that is more susceptible to fireblight for a longer period of time during spring and early summer

Download Sheet from Minn. Dept. of Ag - Fire blight (PDF: 130 KB / 1 page)

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