Skip to main content

Another frost advisory tomorrow morning (5/19/09)

Our low was low 40's this morning. It suppose to be warmer tomorrow and I hope that we do not get any frost damage. We'll see.

We received several disease samples today which I'd like to share with you. The first one is crown gall. This is caused by a bacterium called Agrobacterium vitis. This gall formation is due to genetic modification caused by the bacterium to the infected grape vine. Sometimes it is only a cosmetic damage, but the gall tissue could girdle the vine and restrict the movements of water and nutrients, then results in the death of the vine.

There are some chemicals and biological agent available against gall formation and prevention of the disease, but as far as I know, none of them are very effective as you would expect from other chemical treatments such as fungicides. Removal of the infected vine and then replacing with a certified vine is the common method of management. However, you need to keep in your mind that this bacterium can survive in infected roots and soils up to 5 years. (This bacterium causes a systematic infection, thus if you see the gall, the bacterium can be in roots.) Some of grape phylloxera resistant rootstocks (3309C, 101-14, Riparia Glorie, etc) are known to tolerate the disease.

The other sample is our old friend Phomopsis, caused by a fungus Phomopsis viticola. The first picture shows the case when the rachis is infected. With three weeks of rain after rain, this year has been a Phomopsis year so far.

And the one on your left in this picture is showing splitting of epidermal cell which is also associated with Phomopsis infection.


Unfortunately, we do not have fungicide with a curative activity against Phomopsis on grape. Thus, once the damage has done, nothing much you can do about it to fix it. (You can remove infected shoots at your shoot thinning, though.) You need to remember next spring to protect new growth because the old infected woods can produce spores for 2 years or more.

Comments

  1. Have you had any experience with Gallex a chemical that is supposed to stop the growth of crown gall.
    Dean Scott

    ReplyDelete
  2. Hi Dean,
    Gallex and Galtrol (I think I spelled right), are unfortunately not the solution. One of them uses an antagonistic bacterium, but not very effective. The other help you remove the gall, but R. vitis is systemic pathogen, thus, removal of gall won't help.

    ReplyDelete

Post a Comment

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

Popular posts from this blog

Season's Greetings!

I hope you and your family have a good holiday season and a Happy (and safe) New Year! Thanks again for your support of our programs. Here are some recent media highlights. 😉 The link will open a new window. AHS AREC promotional video  that highlights some of our activities. The link did not work... It asks you to log in to VT. I will request the IT people to change the setting, but in a meantime, here's the same video. We also appeared in  the Library of Congress project “Winery Workers of Virginia”. One more announcement: I will be moving this blog to a new location ( ext.grapepathology.org ) early next year. I had to make a change due to the email subscription service, which has been terminated.  You do not need to change your bookmark or your email subscription. The URL will be forwarded to a new site and your email subscription has been moved to a new site already. 

Recent downy mildew risk events

 It seems that several rain events have happened over the course of the past two weeks or so. Here is a summary of recent downy mildew risk events, based on the NEWA stations and DMCast. Bristol, VA Fifteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Floyd, VA Eleven days with potential DM infection event(s) since Sept 1. The last event happened last Friday. Charles City, VA Twelve days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Central VA Since there was a wide variation among stations, I am listing several around Central VA. Tyro, VA Nine days with potential DM infection event(s) since Sept 1. The latest event happened yesterday. Red Hill and Crozet, VA Only one day with potential DM infection event(s) since Sept 1. Olympic Lake Thirteen days with potential DM infection event(s) since Sept 1. The latest event happened last Sunday. Washington, VA Eight days with potential DM infection event

A quick reminder for late-season disease management materials in preparation for Ida.

  In preparation for hurricane Ida, here is some information that you may find useful (This is a repeat of the previous post, but I received some emails asking for them.) 1)  List of short PHI fungicides for late-season diseases (will open a pdf file) 2)  Updated presentation from the last virtual field day (will open a pdf file). Recent downy mildew risks Many of us have been experiencing more rains lately than the past several months, here are a number of days with downy mildew risk events in the past two weeks based on the NEWA’s DMCast. Many of these rains have been sporadic in terms of area and time it covered, so, use these numbers as a guide. Bristol: 14 days (latest was on 8/30) Floyd: 9 days (latest was on 8/29) Charles City: 14 days (latest was on 8/30) Tyro: 7 days (latest was on 8/30) Red Hill: 5 days (latest was on 8/29) Washington: 8 days (latest was on 8/29) Winchester: 9 days(latest was on 8/29) It is probably a good idea to protect your vines against downy mildew in a