Fire Blight Makes an Appearance

July 07, 2000

Fire blight shoot strike on apple cultivar 'Gala' at UMass Horticulture Research Center, June 29, 2000

Fire Blight has made an unwelcome appearance in Massachusetts orchards in 2000. Shoot strikes are being observed in many orchards, particularly in more susceptible apple cultivars such as 'Paulared', 'Cortland', and 'Gala'. Weather conditions this spring and summer have definitely been conducive to fire blight infection -- these include rain, humidity, and warm temperatures. In addition, wind and hail ('trauma' events) have favored it's spread.

Although fire blight is never good, we should be thankful it is not as bad in New England as in some other apple growing regions such as the Midwest. On the right is a young Gala/M9 orchard in Southwest Michigan with severe fire blight in 2000. A combination of favorable weather conditions, high inoculum levels (Southwest Michigan has had a history of fire blight problems), susceptible cultivar/rootstocks, and streptomycin-resistant bacteria have lead to a very serious problem this season in many Southwest Michigan orchards.

Southwest Michigan orchard of Gala/M9 with a serious fireblight infection, early summer 2000. The grower is facing complete loss of an otherwise productive, young orchard. (Photo by Mark Longstroth, MSU Extension)

Several fire blight strikes on a 'Paulared' tree in Massachusetts, July 6. Infected branches should be removed as soon as possible.

What should you do if you find shoot blight in your orchard? The general rule of thumb is to cut out the infected shoots/branches as soon as they are detected. This usually means walking the orchard weekly and removing fire blight-infected shoots as soon as they appear. Enough of the infected branch needs to be removed to insure the fire blight has not spread back into the tree. This is particularly important in young orchards. Removal of infected branches will reduce the potential inoculum level and help prevent further infection. In nonbearing orchards, a copper application may help too, and is certainly warranted next year at green-tip in blocks where fire blight is observed this season.

Dr. David Rosenberger, Cornell University Hudson Valley Laboratory has written an excellent discussion on the current fire blight situation and how to approach pruning-out shoot blight in infected orchards. Unfortunately, they are dealing with fire blight too after hail destroyed the crop in many Hudson Valley orchards during May.

For more information on fire blight, see:

Fire Blight Fruit Fact Sheet, from the Fruit IPM Program, NYSAES Geneva

Fire Blight, from the West Virginia University Kearneysville Fruit Research and Education Center