concord grape problem

Asked June 17, 2015, 8:01 AM EDT

60+ year old vines, has produced well for years; until about 20 years ago, my Dad sprayed every year with some kind of chemical that is probably no longer available. Last good crop was about five years ago. We prune every year. Very close to the Bay. This year I have sprayed twice so far with Immunox as a fungicide. Grapes grew well and looked very healthy until this weekend when all of a sudden some grapes in each bunch turned brown/dark purple. AAAHHH!! Can you tell me what this is, or what is causing it - and whether Immunox is the right spray to be using? I have mulched (shredded hardwood) around the major vines - could this be affecting anything? Thanks. I can bring in the samples if you can test them.

Anne Arundel County Maryland fruit grape grape black rot

3 Responses

Black rot is a fungal disease that causes brown circular leaf spots, brown on fruit, and reduces many berries to black, shriveled, raisin-like mummies. The fungas pathogan overwinters in the mummified berries from the previous season's crop. So remove all infected fruit, clean up mummies and prune out leaves surrounding fruit clusters for better air circulation and faster drying time..
Spores in the new year are released during wet periods before bloom when new shoots first emerge. Young leaves infected first. Leaves are susceptible to infection for about 1 week until they are fully expanded, however the fruit is susceptible until just before ripening when berry color starts to develop.

Minimize black rot problem by spraying at the correct time:

Two sprays --
1. when shoots are about 1 inch long
2. 7 days later or when new shoot length averages 4 inches (whichever happens earlier)

Immunox is fine.


thanks - so it sounds additional spraying would do no good? I did spray at the times you describe. I probably had too much leftover bad stuff from last year.

Right. It's too late for this year. Now, it's all about removing mummies and infected fruit to reduce infectious material that will reinfect next year.