Phytosanitary Information for Potato

Seed potatoes intended for large scale agriculture are usually produced under certification programs that test for common diseases.  I don’t offer certified tubers because certification programs are not really designed for a small scale operation with lots of varieties like ours.  I still do my best to produce disease free seed tubers.  I test our potato varieties annually and whenever suspicious symptoms are observed. Plants that produce our parent tubers are tested and field grown plants are randomly tested for the common viruses. All varieties listed in the catalog have passed this testing regimen. The tolerance is zero. Any variety with a confirmed positive result will not be offered. This testing program began in 2016.  I only test for viruses known to be present in the USA.  Viruses that are not listed are not tested.

Among other diseases, I do not pass any potatoes that show signs of late blight or black leg.  I would also not pass most other bacterial or fungal conditions, but I have seen few other diseases here so far.  I may pass potatoes with minor common scab, with minor physiological conditions like slight cracking, plants that have recovered from early blight with no signs of tuber infection, or potentially with foliage symptoms that indicate possible phytoplasma, since that condition typically does not affect the tubers.  I would not pass any tubers with indications of powdery scab, but I suspect, based on occasionally seeing scab with papery margins, that it may be present in my soil.  Powdery scab is now nearly as widespread as common scab and it is not always easy to distinguish between the two.  Likewise, I am vigilant for signs of Columbia root knot nematode, but have no indications that it is present here.  None of these are very common here, except for early blight.  Unlike viruses, which are diagnosed with biochemical tests, I diagnose bacterial and fungal diseases based on visible symptoms, so minor cases may escape detection.

Virus Method Schedule Rationale
Alfalfa Mosaic Virus ELISA Once at introduction AMV is somewhat common in heirloom potatoes from private collections.
Andean Potato Latent Virus ELISA Once at introduction APLV has been previously detected in ulluco.  I have never seen it in potato or in any plant in the field and will probably cease testing after 2020.
Beet Western Yellows Virus ELISA Once at introduction for potatoes from private collections west of the Rockies I have never seen a positive result, but I am testing certain varieties that grow in areas where BWYV occurs to determine whether I need to do regular testing.
Cucumber Mosaic Virus Immunostrip Only on suspicion I tested for this for several years with no positive results.
Impatiens Necrotic Spot Virus Immunostrip Only on suspicion We have had some infected dahlias in the past and once got a positive result from potato.
Nepovirus genus PCR Once at introduction There are some rare viruses in this genus that transmit through true seed.  Better safe than sorry.
Papaya Mosaic Virus Immunostrip Annually PapMV is common in many of the Andean tuber crops.  I have never seen a positive result in potato, but it is easy to test for, so better safe than sorry.  Once the collection has settled for a few more years, I will probably stop testing for this.
Pospiviroid genus PCR Once at introduction This is primarily a test for Potato Spindle Tuber Viroid, which is a rare but very bad potato pathogen that could quickly destroy a collection.  This will also catch Chrysanthemum Stunt Viroid.
Potato Leafroll Virus ELISA Annually This is a very common virus and has been present in our field grown plants for years, although it is now rare to get a positive result.  I got no positives for the first time in 2019.
Potato Mop Top Virus ELISA Once at introduction PMTV is a scary virus that can result in long term field infection.  I don’t want it.
Potyvirus genus Immunostrip & ELISA Annually The Potyvirus genus includes some common and damaging potato pathogens like Potato Virus A and Potato Virus Y, both of which have been detected in our field in the past.
Potato Virus M ELISA Once at introduction This is a fairly common virus, but I have never seen a positive in our field.
Potato Virus S Immunostrip & ELISA Annually Potato Virus S is a common potato virus that has been present in our field grown plants in the past.  I have not had a positive result from the field in two years.
Potato Virus X Immunostrip & ELISA Annually Potato Virus X is a common potato virus that has been present in our field grown plants in the past.  We got no positive results in 2019.
Potato Virus Y Immunostrip & ELISA Annually Probably the most widespread and damaging potato virus.  It has been present in our field for years, but I think we may finally be free of it.
Tobacco Mosaic Virus Immunostrip Once at introduction Not common in potato, but TMV is a real pain to get rid of once you have it.
Tobacco Streak Virus Immunostrip Once at introduction We have had previous positive tests for TSV in dahlia, but not potato.
Tomato Spotted Wilt Virus Immunostrip & ELISA Annually I have seen this virus quite a few times in potatoes from private collections and it also infects other Andean root and tuber crops.