Grapes are sick (SECOND REQUEST)

Asked July 4, 2018, 3:14 PM EDT

I never got a response to my question re black spots on my grapes. I am growing a few vines in my backyard arbor. I am attaching photos. Thanks,

Baltimore County Maryland grapes black rot small fruit

10 Responses

I am so sorry your first reply did not make it to your inbox (please see https://ask.extension.org/questions/464165) - if you have additional questions after reading, reply to this note and I will forward to the experts. You may want to check your spam folder.

Looks like too late for this year but may I ask which is likely to work better: Immunox or Mancozeb? The article does not exactly say if the diluted product is sprayed on the leaves or poured in the ground as a systemic. The article says only "treatment" The Immunox may be better for me as it can be applied and wait just 2 weeks to harvest but the Mancozeb leads to a longer delay before eating? Please confirm. Thanks,

This looks like black rot on the grapes, a damaging and common fungal disease of grapes. It is essential to remove and discard 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. We refer gardeners to the Va Tech Spray Schedule for controlling fruit insect pests and diseases.
http://extension.umd.edu/hgic/plants/diseases-grapes
http://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/456/456-018/456-018%2003%20Home%20Fruit.pdf

See Section 3-6, Table 3.3b, Section 3-17, Section 3-18, Table 3.8.

Both Immunox and Mancozeb offer excellent control. They are sprayed and are not poured in the ground. Timing and Days to Harvest are different.
Immunox - do not apply within 2 weeks of harvest and do not apply to grapes more than 6 times per season. Do not confuse with Immunox Plus which is not registered for edible fruit.

Mancozeb - Do not apply within 77 days of harvest.

mh

Many thanks. I ordered immunize today.

Just wanted to mention Section 3-6 'General Information on Pesticides' says
do not apply Immunox to grapes more than 6 times per season.
Table 3.8 'Spray Schedule for Grapes' says do not apply Immunox more than 5 times per season or within two weeks of harvest.
You may want to follow the Spray Schedule.

mh

I have purchased Immunox and will apply at the beginning of the next season as suggested. At this point, I have cut off all the bunches of grapes, most of which have at least some withered grapes. Is there ANY point in applying Immunox now to the leaves, or should I just let them continue to spread and presumably feed the roots until the fall when I would cut everything back to thick stems? I do see some leaves that have brown spots and could cut these away. Question: Apply Immunox now or give up as a lost cause and just start applying with the new season? NOTE: Last year I noticed small nodules on the leaves and almost no grapes, so have been applying SURROUND WP weekly as a protectant. I was told I might have had phylloxera. Thanks, Stan

Apply Immunox next season for black rot. Surround will not help prevent black rot.
We do not have research on Surround and phylloxera. The Surround will not hurt but you will have to wash it off the grapes.

mh

Please take another look at my post above. What if anything should I do NOW even understanding that I am not going to get grapes this season. Does it make sense to spray now or is that worthless and I should just wait until next spring?

Fungal spores from the current leaf and fruit infections can further infect newer leaves through the end of July. After that, spore production diminishes. So spraying at this time would protect younger foliage and would be a good idea.
Most importantly, remove and trash as many infected plant parts as possible to reduce overwintering fungal structures and start spraying with Immunox when shoots elongate in early spring. jt