Black Rot

Asked January 16, 2018, 1:17 PM EST

Hello,

Last year my grapevines and roses both devoloped black rot. I was wondering how do I get rid of this come spring time. How often and when should I start using something? I prefer to go organic if possible. But will do what it takes to elimate this so that I can enjoy a grape harvest and look at my once beautiful roses.


Thank You

Melissa

Kent County Michigan

1 Response

Melissa,
Black spot of roses and black rot in grapes are two separate diseases. Both diseases are caused by wet conditions. The control window of black spot on roses begins when the leaves emerge.
Black spot of Roses, here is a link to an excellent article on Black Spot control from the University of Maine.
https://extension.umaine.edu/ipm/ipddl/publications/5097e/
The leaves are susceptible to infection whenever it rains or when you wet the foliage watering the plant. All the fungicides listed need to be applied before wetting periods to protect the leaves. Many people use a calendar spray schedule of every week or two depending on how rainy it is. There are materials available in many garden sections or garden stores to control black spot. Captan is a common ingredient in many of these pesticides and is relatively save to use and apply and very effective. The Maine article contain both synthetic and organic pesticide recommendations and suggested spray rotations

Grape Black Rot, here is a link to an MSU article on black rot.
http://www.canr.msu.edu/uploads/files/Diseases_PDFs/BlackRot.pdf.
The spores which infect the plant come from last years infected grapes. You should remove all these when you prune the grapes in the spring. The leave infections are not as much of a problem as the fruit infections, so the control window for sprays is not all season long. Sprays should begin as the gapes begin to bloom and be repeated about every 10 days. You did not say what variety of grapes or roses you have and there is a lot of variation between varieties in susceptibility to these two diseases.
I grapes Concord are fairly resistant to black rot and the berries become resistant about 4 weeks after bloom, while European grapes are susceptible until the grapes begin to change color in August. Here again there are products available to use on black rot in garden stores or the garden sections of big box stores.
Read the product labels carefully as most products will not be labeled for use on grapes and roses but some will. Follow the Directions for use in the product labels.