By George W. Sundin and Nikki Rothwell
---- — TRAVERSE CITY — American brown rot is spreading rapidly in dark sweet cherries; these fruit should be harvested immediately to prevent further problems with this disease, local agricultural experts suggested.
Symptoms of American brown rot (ABR) are showing up in increasing amounts within the past 5-6 days. The combination of very warm temperatures and high humidities on top of recent rainfall have all contributed to ABR infection. The ABR pathogen Monilinia fructicola acts very quickly under these conditions; disease stages on an infected fruit can progress from initial infection to a sporulating nightmare in a few days. Unfortunately, when weather conditions significantly favor pathogen infection, it is extremely difficult to keep disease under control.
Dark sweet cherries in particular should be harvested as soon as possible to prevent further ABR infection. With strong storms and high winds predicted for tomorrow July 19, it will be impossible to prevent significant ABR infection to that fruit.
Another sign that sweet cherries should have already been harvested is the occurrence of Alternaria fruit infection. The main sign of Alternaria infection is the presence of a large black spore mass on one side of the fruit. Alternaria infection typically occurs very late in the harvest season. We have observed Alternaria-infected fruit in dark sweet cherry blocks along with ABR this week.
In summary, to prevent further issues with ABR infection, dark sweet cherries need to come off trees immediately.