People and animals are not the only living things that get sick. Plants get sick too. A big part of my job as a viticulturist is to evaluate symptoms and diagnose illnesses in grapevines. Yesterday I went to see a client who noticed some interesting foliar symptoms in her vineyard that brought us to examine the plants further. Red leaves in grapevines look beautiful, but generally are not a good sign.
Red leaves are not efficient performers of photosynthesis, the process in which plants make their own food. While that may not make a big difference in your garden at home, it is a problem when you are growing a crop to sell for profit (hopefully).
In this case, I thought that the foliar symptoms pointed to a bacterial infection called Crown Gall. Crown Gall is caused by the bacterium Agrobacterium tumefaciens which infects the tissue of the grapevine by entering a wound on the plant. At this vineyard, the wounds were probably caused by severe cold temperatures that made cracks in the trunk of the vine creating a wound in which the bacterium could enter the plant tissue.
The cracks from the cold temperatures look like this:
The infected tissue that I thought was Crown Gall looks like this (It’s the stuff that my daughter says looks like brains. In the first picture there is some right where the soil and the trunk meet, and some higher up just below the graft union. In the second picture it runs down the right side of the trunk from the top of the wound to the soil.):
Because I don’t have a lot of experience with Crown Gall I wanted to get a second opinion from someone with more technical viticulture experience than me. I called Mark Battany, our local Viticulture Farm Advisor. After our telephone conversation I sent him some photos of the symptoms that I saw. He emailed me back to explain that what I was thinking was tissue infected with Crown Gall was actually callus tissue which is a grapevine’s response to severe wounding. Sort of like how our skin makes a scar when it is injured. He went on to explain, “This type of wounding, in which all of the outer cambium tissue has essentially disappeared AND the vine responds with callus growth, is often associated with herbicide damage.”
So my initial diagnosis was incorrect. But I learned so much yesterday solving this mystery! I love that! And part of the message here is to be humble. You can’t know everything, and it’s ok to ask for help from someone who knows more than you do, then use that knowledge that is gained to help someone who knows less than you do.
How’s that for the lesson of the day?