Bacterial canker and cold spring temperatures

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Bacterial canker is caused by the bacteria Pseudomonas syringae, and this pathogen can infect sweet and tart cherry and plums throughout Michigan. This disease is most problematic in sweet cherries, and epidemics often occur in conjunction with cold, frost-prone weather in the spring. Freezing temperatures can also dispose cherry tissues to bacterial canker infection, especially if the freeze event is followed by wet weather. Therefore, growers should be particularly diligent about early bacterial canker control in the coming weeks after these cold spring temperatures.

Early copper sprays are the most common methods of control for bacterial canker on cherry. However, sweet cherry tissues are extremely sensitive to copper, and the sprays must be adequately timed to reduce P. syringae inoculum without causing phytotoxicity. If the trees are still in the dormant stage, two copper applications can be applied at one to two week intervals at a rate of 1.2-2lbs of metallic copper with either one pint of spray oil per 100 gallons of water or 6-9 lbs of hydrated lime per acre. Copper products sprayed during the dormant stage should have good retention properties to enhance disease control as longer residuals for copper should translate into an extended period of bacterial disease suppression after the spray is applied (Rosenberger, 2007).

If the trees have broken dormancy and are in the pre-bloom stage (bud swell, side green or green tip), copper rates should be reduced to 25 to 35% of the dormant rate. Up to two copper applications with a one week interval should be used at this time. No copper applications should be made once any white can be observed on the tree. In tart cherries, copper compounds can be used at the 1.2-2lb actual copper rate at bud burst with weekly repeated applications until late May. Some of these later sprays may result in some leaf yellowing, bronzing, and potentially defoliation. Adding hydrating lime at 6-9 lbs/acre will reduce the phytotoxic effects of copper, but we do not recommend applying copper at temperatures above 75 degrees (F).

Literature cited: Rosenberger, D. 2007. Early season copper sprays. Scaffolds Fruit Journal. April 9. 16:4.

Dr. Sundin’s work is funded in part by MSU‘s AgBioResearch.

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