Tuesday, August 16, 2016

Last stretch!!

I heard that some of early cultivars are ready to be picked on 7-10 days.  Looks like no tropical storms to worry, yet... (crossing my fingers!)

There have been frequent thunderstorms went through our area, and some of them (like the one we had last night) resulted in a significantly long wetness event (8 hours). These wetness events, especially the one happens overnight, are preferred by downy mildew pathogen since they produce spores in dark, moist conditions.

Please check my previous post on late season downy mildew. As usual, protection is the best approach.  If you have seen some downy mildew on foliage, it would be best if you can mix a protective material (e.g., copper, captan) with a phosphonate (Prophyt, Phostrol, etc). If there is heavy downy mildew already happening, please do not use Ridomil (metaxel) products because they are known to be overcame by the downy mildew pathogen.

Some of reds are probably going through veraison, which would be a good timing for your Botrytis application. Make sure to rotate mode of action since Botrytis is known to develop fungicide resistance. Please refer to my previous post for details on Botrytis management.  Also note that as with Botrytis, a key for sour rot management is the protection of fruits from any wounding events (birds, insect, human activities, etc). These pathogens tend to take advantage of existing wounds.


4 comments:

  1. Dr Nita, thank you for this wonderful blog. You mention tank mixing copper + phosphonates. I was under the (mistaken?)belief that this combo could cause phytotoxicity? Am I mistaken in this?

    ReplyDelete
  2. Does anyone have a suggestion regarding what o do if your grapes ripen before the 66 pre harvest interval for mancozeb?

    ReplyDelete
  3. As for copper + phosphonate. The phytotoxicity seems to happen when 1) pH of water is off from the recommended range for phosphonate or 2) concentration of phosphonate is too high. Thus the combination itself seems not the cause of the issue, in fact, I learned that there is a combo product sold in other countries. In anyway, since the combo can potentially cause damages, please try it with a few vines before you apply to the whole vineyard.

    Hi John,
    Well, the label is a legal document, and you need to follow it. You just have to wait until the pre-harvest interval is over.

    ReplyDelete
  4. Thank you for the answer. I am just a backyard vintner. I understand the legality of the issue just wanted to know if I die if I pick the grapes make the wine and drink it.

    ReplyDelete

Please leave your comment here. In order to avoid spam messages, I'll moderate comments, thus it may take a few hours for your comment to be posted on the page.