Skip to main content

Notes on Phomopsis

 It seems that we will observe sunny days with 60-70F for next few days.  Hopefully, the night time temperature won't drop too low.  Our Chardonnay vines are showing a little bit of deformation on leaves, probably due to the low temperature during the night.  Unless we will have more cold nights, it should overcome the stress.

 Most of our early varieties (e.g., Chardonnay, Merlot) are in this stage (1-2 inches long).  Please note that the flower cluster is already exposed at this point.  Fortunately, we are not expecting a rain event soon, but at this point, the shoot is susceptible to Phomopsis.  If the fungus successfully infects rachis tissue, it may cause a premature fruit drop later in the season.

 The picture on the right was taken last year.  As you can see, a part of rachis became necrotic due to Phomopsis infection, and berries were dropped because the rachis is dead.
 The fungus survives in canes and trunks that are infected in previous years, and during the spring it will produce spores that are splashed by rain onto new tissues.  Thus, it is important to protect young tissues when it is close to the older canes and trunks (i.e., now!).

 It requires rain event to cause infection, thus you need to monitor your local weather forecast.  If a rain is coming into the picture, mancozeb (Penncozeb, Dithane, etc.) is an effective protective material against Phomopsis.  At this point, no materials are effective after the infection.


Popular posts from this blog

2021 Pest Management Guides for grapes (UPDATED 24 March 2021)

Updated: Links below are for the 2021 edition of Pest Management Guides. The first one is for home gardens, and the second is for commercial productions. I asked them to provide by chapter (= crop) and they made changes. :) 1) Visit the page by clicking one of the links below. (It is rather a slow page. Please be patient.) 2) Scroll down until you see "Links to individual chapters." Grapes are chapter 3 for both Home (Home Fruits) and Commercial Crops (Grapes) 3) Once you get to the site, click "PDF", then "Preview", and it will open a new window.  4) Scroll down a bit, and click "Download Version" to download the file to your computer.  2021 Home Grounds  Pest   Management   Guide 2021 Horticulture and Forest  Pest   Management   Guide

Prepare for a potential rain event for this weekend.

Looks like a tropical storm Marco is moving westward, but Laura may hit our areas during this weekend. The current forecast shows (opens a new window with a link to potential movement to Virginia and surrounding states around this Saturday (8/29). Many white cultivars will be either ready to pick or getting very close to harvest, and red cultivars may have several weeks to go, depends on where you are what you grow. At this point in the season, the target diseases are late-season fruit rots (Botrytis, ripe rot, bitter rot, etc.) and downy mildew (on leaves). For whites, it may be a decision of when to pick, but not what to spray. If you decided to wait until the storm is over, there are several materials with a very short PHI that you may want to consider, such as Oso/Ph-D or Elevate for Botrytis and a phos acid for downy mildew. FYI: when we tested in the field, Oso plus Double Nickel combination worked well against sour rot. For reds, it will depend on when and what you

Downy, Botrytis, sulfur burn, and open house

With recent rain events and warm and humid nights, the risk of downy mildew and Botrytis are probably high in many areas of Virginia. For example, I counted seven days (at Winchester, VA) and eleven days (at Rustburg and Scottsville, VA), with downy mildew infection events in the past two weeks according to the NEWA model ( ). It is very important to keep your vines protected, and if you think you need to have a kick-back activity against downy mildew to counteract the recent rain event that your previous spray might not have provided good coverage, add a phosphorous acid material such as Prophyt or Phostrol.  Please refer to this list of materials with short PHI since some of the cultivars are getting very close to harvest. Note: although both sulfur and copper have a short PHI, we typically do not recommend spraying these materials within 3-4 weeks of harvest due to its potential negative impacts on the fermentation or wine quality.  When some of us ended up