The Fruit Growers News

The fire blight epidemic in Berrien County is as severe as I have ever seen. Many acres of high-density plantings have been severely affected. These orchards will be destroyed as economic units by the death of most of the trees.

This epidemic will change the way we grow apples in Southwest Michigan. A few growers avoided fire blight susceptible varieties on dwarfing rootstocks, while others planted the new premium varieties believing they could control the disease. After this season I doubt few growers will chance it again.

This epidemic caught some of us by surprise. Perhaps we were too fixated on the need for rain to start an infection period. Fire blight symptoms began to appear in Idared and Jonathan trees several days earlier than predicted by the Maryblyt model. Backtracking from the date of the symptoms indicates that the infection took place on May 4, when the epiphytic bacteria levels first reached high levels. There was no rain or dew on this date and the relative humidity ranged from 83% to 43%. Wind data from the Southwest Michigan Research and Extension Center indicates that 15 mph was the average wind speed for the day. Apparently the infection was due to warm, humid and moderately, windy conditions. There were also three infection periods associated with rain and high temperatures during apple bloom.

As the symptoms of the rain-induced blossom infections began to appear, a cold front with widespread hail and thunderstorms spread the disease to many more blocks. The blossom blight symptoms appeared mainly in unsprayed blocks of susceptible varieties, as well as varieties such as Golden Delicious that do not normally get fire blight.

Fire blight strikes can be found on varieties that are normally very resistant such as Empire, McIntosh and Red Delicious. This indicates we had extremely high levels of inoculum and good infection conditions. Growers who applied antibiotics after rains suffered more as they were hard pressed to cover all their acreage.

At the beginning of June, another wave of fire blight symptoms began to appear in all susceptible varieties as a result of the hail and wind.

The symptoms from this infection are pretty severe and would have most Michigan growers concerned about the health of their orchards, but this year growers are happy that it is no worse. My advice to growers with severe fire blight is to go fishing. There is no spray or cure for fire blight once it is in the trees. If there are only a few strikes in the orchard, then pulling out shoots makes sense, but when there are multiple strikes in each tree then waiting until the disease stops spreading is a good option. Many Southwest Michigan growers have abandoned their crop and are spraying with copper, hoping to slow the spread of the disease.



		Fire Blight Epidemic Strikes SW Michigan By Mark Longstroth Michigan State University Extension The fire blight epidemic in Berrien County is as severe as I have ever seen. Many acres of high-density plantings have been severely affected. These orchards will be destroyed as economic units by the death of most of the trees. This epidemic will change the way we grow apples in Southwest Michigan. A few growers avoided fire blight susceptible varieties on dwarfing rootstocks, while others planted the new premium varieties believing they could control the disease. After this season I doubt few growers will chance it again. This epidemic caught some of us by surprise. Perhaps we were too fixated on the need for rain to start an infection period. Fire blight symptoms began to appear in Idared and Jonathan trees several days earlier than predicted by the Maryblyt model. Backtracking from the date of the symptoms indicates that the infection took place on May 4, when the epiphytic bacteria levels first reached high levels. There was no rain or dew on this date and the relative humidity ranged from 83% to 43%. Wind data from the Southwest Michigan Research and Extension Center indicates that 15 mph was the average wind speed for the day. Apparently the infection was due to warm, humid and moderately, windy conditions. There were also three infection periods associated with rain and high temperatures during apple bloom. As the symptoms of the rain-induced blossom infections began to appear, a cold front with widespread hail and thunderstorms spread the disease to many more blocks. The blossom blight symptoms appeared mainly in unsprayed blocks of susceptible varieties, as well as varieties such as Golden Delicious that do not normally get fire blight. Fire blight strikes can be found on varieties that are normally very resistant such as Empire, McIntosh and Red Delicious. This indicates we had extremely high levels of inoculum and good infection conditions. Growers who applied antibiotics after rains suffered more as they were hard pressed to cover all their acreage. At the beginning of June, another wave of fire blight symptoms began to appear in all susceptible varieties as a result of the hail and wind. The symptoms from this infection are pretty severe and would have most Michigan growers concerned about the health of their orchards, but this year growers are happy that it is no worse. My advice to growers with severe fire blight is to go fishing. There is no spray or cure for fire blight once it is in the trees. If there are only a few strikes in the orchard, then pulling out shoots makes sense, but when there are multiple strikes in each tree then waiting until the disease stops spreading is a good option. Many Southwest Michigan growers have abandoned their crop and are spraying with copper, hoping to slow the spread of the disease.












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