PPDL Picture of the Week for

August 31, 2015​

Brown Rot on...Apples?​

Janna Beckerman, Associate Professor, Botany & Plant Pathology Dept, Purdue University

For many of us across Indiana, we’ve received almost twice as much rain as normal. One of the many consequences of this is the unusual disease activity. At Meig’s, we are seeing the beginnings of bitter rot, especially on HoneyCrisp, and an uptick of black rot. These were expected. What was not was the obliteration of Pristine by brown rot(Fig. 1).

In the course of my career, I’ve only encountered brown rot as a sole cause of disease on apples once before—and it was Monilinia laxa, which causes European brown rot, and it happened in Minnesota. Most of the time, brown rot is associated with injury (often bird injury). This was not the case in the fruit examined, although insect injury could not be entirely ruled out. Furthermore, the incidence of disease exceeded 20%.

Symptoms and signs of brown rot on apples included brown spots that quickly expand throughout the fruit, followed by brown tufts of fungus (Fig. 2). These tufts produce thousands of spores (conidia).

The disease triangle describes the interactions of a susceptible host, virulent pathogen, and conducive environment. This year, unusually wet weather, coupled with a susceptible host and inoculum, created a perfect storm. We don’t expect to see this next year, but we will be keeping our eyes open. If you’ve seen this in your orchard, please drop me an email.

Janna Beckerman, jbeckerm@purdue.edu

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​​Click Image to enlarge

 Figure 1

  Figure 2