Win Cowgill, Professor and Area Fruit Agent
Bacterial Canker continues to be a serious bacterial disease of cherry in New Jersey as well as all other regions where the climate is humid.
Bacterial canker has been very active this season in NJ in both sweet and tart cherry blocks.
Bacterial canker or bacterial gummosis of sweet cherry is caused by several Pseudomonas bacterium. This disease infects flower buds and spurs. It can completely kill new spurs and leaves and then move into the trunk on cherry. This is especially problematic with our new Geslia Dwarf cherries as losing a scaffold or getting infection into the trunk will limit production as the tree rapidly declines.
We should avoid large, dormant pruning cuts; and use summer pruning to minimize the impact of the disease.
Control Now with Copper
Begin spraying now to control Bacterial Canker. Cankers get started mainly in the fall after most of the leaves have fallen and the trees are beginning to go dormant.
The only effective way to control this disease is to reduce the number of bacteria before the trees enter their susceptible period. The bacteria that start these cankers are found on the surfaces of mature leaves and other green tissues, and do not come from existing cankers.
The only successful control we have found is repeated applications of the old Bordeaux mixture in September, October, and November and repeated again in the spring. Bordeaux Mix consists of hydrated lime (Builders Lime) and Copper Sulfate. The rates and methods of mixing are important. We begin our sprays the second week in September.
Note however that sprays of Bordeaux applied to green leaves must be saftened with vegetable oil (Canola) to avoid burning the foliage. Four additional sprays 14 days apart will be applied.
Bordeaux mix will also be applied in the spring with several applications before bud break.
It would be my recommendation that in all cherry blocks a program of Bordeaux Mix applications should be made this September before the next rain. Careful observation and scouting of older blocks should be done now to determine if this bacterial disease is present and control warranted.
It is my observation to date that if any Bacterial Canker is observed in sweet cherry I would plan a spray program of Bordeaux mixture.
Use only powdered copper sulfate (bluestone or blue vitriol), often referred to as copper sulfate “snow” because it is finely ground and dissolves relatively quickly in water, to prepare tank-mix bordeaux.
Ordinary lump copper sulfate is not satisfactory. Store copper sulfate snow in a dry place. Moist snow becomes lumpy and is difficult to work through the screen into the tank. Use copper sulfate registered to make bordeaux mixture.
To prepare tank-mix bordeaux, use only good quality hydrated lime (calcium hydroxide) also called builders lime. The hydrated lime should be fresh, that is, not carbonated by prolonged exposure to air. Hydrated lime is stable and usually is readily available under several trade names. Magnesium lime, a mixture of Ca(OH)2 and Mg(OH)2, may also be used.
Bordeaux formulas are stated as three hyphenated numbers: 8-8-100. The first number refers to the pounds of bluestone (copper sulfate), the second number to the pounds of spray (hydrated) lime, and the last number to the gallons of water to be used. Thus, an 8-8-100 bordeaux contains 8 lb copper sulfate, 8 lb spray lime, and 100 gal water.
Have your tank ½ full of water and the agitation turned on, then add the copper sulfate or copper sulfate solutions, then the hydrated lime solution, and then add the Canola Oil at 2.8 quarts/100 gallons to saften the mix for the foliage.
In a research trial at the Rutgers Snyder Farm, Champ DP copper was also evaluated against Bordeaux mix for phytotoxicity on cherry. The oil equally saftened Champ DP as it did Bordeaux.
Caution, Champ2 Flowable may not be compatible with the vegetable oils; all copper mixes should be jar tested before adding to your spray tank.
Note: In our humid climate in New Jersey the cankers can continue to develop in lateral branches and the central leader. In some cases the cankers have grown to girdle and kill two-year wood. I have observed central leader dieback as a result. In older wood the canker looks very much like a fire blight canker in apple. In most cases the canker begins to ooze a brown to amber exudate. It appears that under our humid conditions this disease is very hard to control and can be devastating if control measures and the proper horticultural practices are not followed.
This bacterial disease is most troublesome in young plantings where it can cause loses of up to ten percent of the trees. On mature trees it can reduce yields from 10–50%.
Many growers who did not think they had bacterial canker are beginning to see it on three and four year old trees.
The source of inoculum may come from wild cherry trees in our hedgerows, Black Cherry; Prunus serotina may be one source of inoculum for the Pseudomonas during wind and rainstorms in the spring and summer months. Removal may be beneficial.
Fact sheets on Bacterial Canker
There are numerous fact sheets online for Bacterial Canker; many include color photographs for reference. Below are the listings for several:
Ontario Canada written by W.R. Allen “Bacterial Canker of Sweet Cherry” NO. 88-0886.
It has good color plates and lists control measures.
West Virginia University
Comparison of healthy trees vs. diseased trees:
University of California
For additional information please do not hesitate to contact me, Win Cowgill