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  • From: "Barry Jackson" <barry.jackson AT which.net>
  • To: <market-farming AT lists.ibiblio.org>
  • Subject: [Market-farming] RE: Market-farming ,Root Nematodes
  • Date: Sat, 17 Apr 2004 00:10:10 +0100



> -----Original Message-----
> From: market-farming-bounces AT lists.ibiblio.org
> [mailto:market-farming-bounces AT lists.ibiblio.org]On Behalf Of
> market-farming-request AT lists.ibiblio.org
> Sent: Wednesday, April 14, 2004 2:58 PM
> To: market-farming AT lists.ibiblio.org
> Subject: Market-farming Digest,Root Nematodes
>
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Hi,
Bob Higgins wrote
> "Last year, a large percentage of my potatoes came out gnarly and
> deformed. This was in my new garden, first market garden, new
> place we moved to. First I thought the potatoes looked like that
> because I let the weeding go and they had to compete with lots of
> strongly-rooted weeds -- maybe the weed roots wrapped around the taters.

It struck me that this was very similar to my own problems last year where I
was growing PCN susceptible potatoes (King Edwards) in 100% home made
compost in raised beds 1ft deep to avoid the debilitating effects of our
endemic eelworm. [This incidentally was on the west coast of the UK, much
closer to Jersey than New Jersey]

In trying to find out how/why my lumpy potatoes had become so deformed I
unearthed the two leads below. I suspect if you do a Google search on
"stressed potatoes" you will find many more.
We had a fairly warm summer here but crucially in my deep raised beds the
soil temperature would have been rather higher than was experienced in the
normal soil plus the irregularity of my watering regime no doubt added an
additional stress.
I feel sure the tuberisation of my potatoes was halted by heat or moisture
stress and, when cooler conditions came along, they simply started growing
secondary potatoes from dormant eye sites of the original tubers.
Perhaps in your case the vigorous weeds might have created a condition of
moisture stress.
Did you have a closed canopy?

Best of luck for this year.
Barry Jackson, Parkgate, Wirral UK.

http://www.uga.edu/vegetable/potato.html
This is a lengthy paper & I have paraphrased below what I think is the
relevant bit.
"The optimal temperature for tuberization is 55?F, the process actually
decreases above 70?F and for certain cultivars, may stop altogether at 85?F.
Higher temperatures may often induce knobbliness and secondary growth in the
tubers. Maximum yields are usually obtained when the average growing
temperature is kept between 60? and 65?F

Irrigation before tuber initiation can adversely affect both the yield and
the marketability. A consistent soil moisture of 60-70% of field capacity is
crucial particularly during tuber development. Fluctuation in soil moisture
content may well give rise to abnormalities in tuber formation."

AND from
http://www.plantpath.wisc.edu/wivegdis/2002%20veg%20dis%20updates/Potato%20C
rop%20Update%20Number%205%2007-03-02.htm

Potatoes are heat sensitive and Russet Burbank is one of the most heat
sensitive varieties grown in the United States. Photosynthetic efficiency or
net photosynthesis in potatoes rapidly declines as temperatures increase
above 85? F. As a result the plant has less carbohydrate from photosynthesis
to support growth and more importantly tuber development. When heat stress
becomes severe or prolonged over extended periods of time, tubers will stop
bulking altogether and may start to lose mass as starch is degraded to
provide energy to maintain the stressed plant. Unfortunately, when
conditions become favourable for active tuber growth again, potatoes do not
simply start bulking the same tubers. Rather, potatoes will go through
secondary set or initiate tuber growth at one location on the tuber. The end
result is smaller potatoes or malformed tubers with irregular growth.
Little can be done to manage heat stress in potatoes. Closed canopies are
absolutely essential for managing the temperature of the hill.






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