Fireblight or Not

Fireblight is caused by a bacterial infection (Erwinia amylovora). Fireblight affects a wide range of trees in the rose family. The symptoms are that the leaves and flowers near the growing tips wilt, turn red and look as though they have been burnt by fire. These leaves turn brown and remain attached to the branch. The new growing tips have a “shepherd’s crook” at the ends. Cankers, which are usually black, can develop later on the trunk. They typically ooze liquid. Fireblight can be spread by rain, wind, pollinating insects, and pruing shears. The only certain way of identifying fireblight is to do a petiole squash, and check for many motile bacteria under the microscope. No one can tell just by looking at the tree. There are certain tree removing companies in Brandon who are advising individuals that they have fireblight when in fact they do not. There have been no cases or fireblight this year out of many samples.

This year [1997] once again we have been seeing a lot of fungal disease caused by a Cytospora sp. Some of its symptoms may be similar to fireblight. Apparent nutrient deficiences, (leaves go coppery brown in color), which are not seen in fireblight.

The control for both of these problems is to cut out any dead wood. One can check for dead wood by taking a sterile knife (razor blade) and pealing the bark back just a small amount. If the wood underneath is brown, it i dead and if it is green it is alive. This dead wood should be cut back into healthy wood about four to six inches. One should sterilize their pruning shears after each cut, in one part bleach to nine part water. The cankers should be cleaned out with a knife. The tree should be sprayed with Later’s copper after it has been pruned.

To prevent cracking of the barck in the winterone should paint the main trunk with white latex paint or white wash. This reflects the sun’s rays and then prevents the sun scald, which encourages disease. Another measure to prevent disease is spraying apple trees with dormant oil in October. This prevents drying out, which weakens branches and tips and allows fungi to enter the tree. To prevent excess winter drying only fertilize trees first thing in the spring. This gives the tree time to harden for the winter preventing soft lush growth in the fall.

By Dr. Paton and Vicki East