anthracnose?

Asked July 3, 2018, 2:54 PM EDT

There is a grape vine in the Demonstration Garden in Derwood, which has round brown blemishes on the fruit. Other fruit have withered completely. I don't remember if there are blemishes on the leaves and/or trunk too. It seems like anthracnose? What to do about it? Prune all infected parts and dispose of? Only at the end of the season, or now to prevent further propagation of the disease? Sprays or other treatments? As you know, there were several torrential rains earlier this season. How does one mitigate against such fungal enhancing weather? In addition, the newest leaf shoots are bleached almost completely white, although the older leaves are green. I I don't know of any soil changes made this season to suddenly cause chlorosis, if that is what this is. Treatment while waiting for soil test or checking our records? FeSO4 to soil? Foliar spray?

Montgomery County Maryland grapes fruit black rot soil test

1 Response

This is not anthracnose. This looks like black rot, a common and damaging fungal disease of grapes. It is essential to remove and discard (now and at the end of the season if need be) as much of the infected fruit as possible to reduce disease incidence next year.

The fungus causes leaf symptoms early in the season and then infects the fruit. Spraying preventatively early in the season (when shoots begin to elongate) is essential. It is too late to spray this year. Take a look at information on grapes, black rot, and the Va Tech Spray schedule
http://extension.umd.edu/hgic/plants/grapes
http://extension.umd.edu/hgic/plants/diseases-grapeshttp://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-018/456-018%2003%20Home%20Fruit.pdf

There may be several reasons for the pale foliage. Could be nutrients washed out of the soil due to all the rain we had this season, environmental issues, etc.
We do not see any interveinal chlorosis. Do not add any iron sulfates or amendments now.
It would be okay to test the soil as it may reveal something. Results will give you pH and nutrient deficiencies. http://extension.umd.edu/hgic/soils/soil-testing

mh