Ten step program to manage bacterial canker of sweet cherry

Sweet cherry is crop that continues to be of great interest to Indiana growers. It also continues to be a challenge due to bacterial canker, caused by Pseudomonas syringae. This bacterium is a significant pathogen of young sweet cherry trees killing 10 to 20 percent of the trees in new orchards within 5 years of planting. I’ve modified Dr. Robert A. Spotts, OSU Mid-Columbia Agricultural Research and Extension Center, Hood River, OR, suggestions for the integration of several techniques that are more appropriate for Indiana growing:

1.Do not interplant new trees with old trees, which are major sources of P. syringae. Think about it! Any old, infected trees serve as inoculum to infect new trees!

2. Keep irrigation water off the part of the trees above ground as much as possible for the first 2 or 3 years after planting. If irrigating, consider withholding water in late summer so trees will “harden off” and not be as susceptible to low temperature injury in early winter. If you were wondering about a lot of the dieback your stone fruit had last season, now you know. Unfortunately, there is little we can do about the weather.
3. Avoid all types of injury—mechanical, insect, frost. Paint all trunks white with latex paint to prevent winter injury. Adding copper to the paint is probably of little benefit.
4. Some studies show less bacterial canker when pruning is delayed until spring, even as late as after flowering in May. Less disease also occurs when summer pruning is used. Prune only during dry weather if possible.
5. Remove branches and trees killed by P. syringae from the orchard and destroy them. Take care while pruning to minimize the potential spread of bacteria.
6. Mazzard F12-1 is one of the most resistant rootstocks. Resistance of new rootstocks is unknown at this time, but trees on Mazzard may have an advantage over trees on size-controlling rootstocks. Sweet cherry scion cultivars are all susceptible to varying degrees.
7. Locate the orchard in an area less likely to be affected by frost and slow drying conditions.
8. Provide optimal soil conditions for growth of cherries, including attention to pH and nutrition. Application of excess nitrogen, especially late in the growing season, will promote late-season growth that is susceptible to low temperature injury in early winter, followed by bacterial infection.
9. Control weeds, especially grasses. They often support large populations of P. syringae. Clover and vetch ground covers support lower populations. Consider clean cultivation of row middles for the first 3 years.
10. Application of fixed copper products or Bordeaux 12-12-100 is no longer recommended. In recent research trials, these treatments resulted in higher damage than that in untreated controls.
    

    

    Figure 1. Bacterial blossom blast, a symptom of bacterial canker of sweet cherry caused by Pseudomonas syringae pv. syringae. Photo by George Sundin.

    

    Figure 2. Bacterial blossom blast, a symptom of bacterial canker of sweet cherry caused by Pseudomonas syringae pv. syringae. Note: essentially all spurs on this tree are affected by blast. Photo by George Sundin.

    

    Figure 3. Bacterial canker of cherry. Photo by George Sundin.

    
    

    

    Figure 4. Leaf Spot Symptoms. Photo by George Sundin.

    

    Figure 5. Gummosis. Photo by Janna Beckerman