OLive Knot disease

Asked May 17, 2013, 7:54 PM EDT

Does the Olive Knot Bacterium exist on olives in Oregon? If so, what are the best preventative programs if one was to grow olives there?

Tulare County California

3 Responses

Hi - that's a great question. So far as I know we do not have olive knot on olive in Oregon. We do on occasion have a similar problem on forsythia caused by a related bacterium. However, in the 20 years that I have been diagnosing plants in Oregon, I've seen that disease (on forsythia) only about 3 times.

Since we don't yet have the bacterium here on olive, I would not suggest any sort of preventive sprays. I would strongly suggest though, carefully examining new planting material obtained from areas where olive knot does occur. If any knots are found, do not use any of the material, as plants bundled together with a symptomatic plant would be at risk of developing the disease.

I hope this is helpful.

Kind regards,
M. Putnam


Thank you for the response. Is there any written documentation the olive knot bacterium (Pseudomonas savastanoi) indeed exists on (infects) Forsythia? THanks.


Hi Steve,

Well, I thought it had been published somewhere, but I guess not. I know that the knots on Forsythia have been observed for years, and it has been misdiagnosed for decades.

I found one very old reference to Agrobacterium tumefaciens (the crown gall pathogen) on Forsythia, but that was probably a visual diagnosis without confirmation. In my lab we have isolated P. savastanoi from Forsythia galls and confirmed the ID of the bacteria recovered by sequencing one of its genes, and I did present that information at a meeting. However, the proceedings of the meeting were not published, so I guess I need to get that information in the public domain.

There are images of the bacterial galls at http://oregonstate.edu/dept/nurspest/Phomopsis%20Forsythia%20stem%20gall.html.

Melodie Putnam