Wednesday, December 11, 2013

Analysis of diseased garlic cloves

Last year I wrote about a mysterious "waxy" substance on my harvested garlic cloves. I chalked it up to "oh well, try again next year." We discarded or cut out the waxy parts and didn't use them to plant the 2013 crop.

In July, I harvested the crop and hung them in the garage to dry and cure. In October, I cracked open dozens of crowns to find the fattest cloves for planting the 2014 crop, and to my dismay, I found more of that waxy substance, plus some rotten looking cloves.

This time, I knew who to call, and handed some samples over to Brian Hudelson, senior outreach specialist with the UW-Extension plant disease diagnostics clinic. Each summer Brian pays our community garden a visit and is always interested in seeing dead and dying plants. I thought he'd enjoy seeing these samples.

I received an analysis today, and here's what Brian wrote.

Dear Josh:
I have completed the analysis of the garlic sample that you submitted to the Plant Disease Diagnostics Clinic. I initially showed your sample to Phil Pellitteri, our insect diagnostician, for comment. Phil found evidence of Indian meal moth larvae in the sample. This insect tends to attack stored garlic. Please see the attached fact sheet for details on this insect pest and its management. Phil also found evidence of bulb mites in the sample, but commented that these mites are commonly found in soil and likely invaded your garlic after it had been compromised by other factors.

I subsequently used standard isolation techniques in an effort to recover disease-causing organisms from your cloves. I did recover some Fusarium from the materials that you provided and this fungus can cause clove rot issues on garlic. I am enclosing a photocopy of some information on the disease caused by this fungus. In addition, I believe that part of the problem with your garlic may be something called waxy breakdown, a high temperature-related physiological disorder. I am enclosing a brief description of this disorder as well.

In terms of management, I think the best way to proceed is to simply inspect the cloves you have in storage, and dispose of any with significant blemishes and/or discolorations. If you decide to use any of your cloves to replant next year, be sure to reinspect them prior to planting and use only blemish-free cloves. Also try not to replant in the same area of your garden plot where you had garlic last year.

I hope this information is of help to you. Please let me know if you have any questions. Thanks again for using the Plant Disease Diagnostics Clinic.

In conclusion:
  • I did not use any of the waxy cloves for next year's crop. In fact, one species seemed to be particularly affected and we ate or destroyed all those cloves.
  • I'm going to put a moth control strip near my garlic.
  • I did rotate the garlic into a new bed.