April 2020 - 14

The University of Idaho's potato conference at Idaho State University in Pocatello was well
attended with 582 registrants and more participants who attended but didn't formally register.
Jackson Allred, who raises Norkotah, Ranger
and Burbanks in Burley, Idaho, talks about
potato varieties with Allan Landon, a sales
rep with Syngenta in Idaho Falls, left, and Jeff
Stark, director of potato variety development
programs for the University of Idaho.
Jeff Miller, a plant pathologist, president
and chief executive officer of Miller
Research in Rupert, described use of
fungicides to combat soilborne pathogens
that cause pink rot and Pythium leak.
" Proper irrigation management to
avoid excessive moisture at harvest goes
a long way to prevent the diseases, " he
said. " When temperatures are over 70
degrees, it increases the risk of infection. "
The interior of potatoes affected by
pink rot will turn pink after being sliced
and exposed to warm air for about 15 to
20 minutes. Research has shown that
adjusting soil pH by lime application in
low pH soils can help prevent it.
To manage it postharvest, he suggested
using several fungicides containing
mefenoxam/metalaxyl,
phosphorous
acid, cyazofamid or ethaboxam.
Potatoes with skin wounds can
become infected with Pythium leak. The
14
Spudman.com
Florentino Jaquez, manager at Jentzsch
Kearl Farms in Rupert, Idaho, learns about
a high-speed separator manufactured by
LOCKWOOD that uses a vacuum chamber
to remove rocks and other debris. Photos:
Dianna Troyer
diseased potatoes are often extremely
moist and in some cases when squeezed,
clear liquid comes out. To avoid it,
potatoes should be harvested at cooler
time of day. He advised growers to make
sure tuber pulp temperatures are 55
degrees Fahrenheit or lower in storage.
Unfortunately, a foliar phosphite
fungicide program is not effective
against Pythium leak, he said.
Clearwater is more susceptible than
Burbank, Alturas, or Dakota.
Miller keeps his website updated
with the latest potato research at www.
millerresearch.com
To avoid damaging potatoes' skin and
making them susceptible to disease,
plant pathologist James Woodhall,
advised allowing at least 21 days after
vine kill for good skin set before harvest.
" Studies at the University of Idaho
showed tubers harvested four weeks
after vine kill developed less dry rot
in storage compared to those two
weeks after vine kill or green dug, "
said Woodhall, who works at the UI
Research and Extension Center in
Parma. " Harvest when tuber pulp
temperatures are between 45 and 65
degrees Fahrenheit. "
Woodhall said a soilborne fungus
Rhizoctonia solani AG3-PT is a
predominant strain in potato seed in
Idaho. Symptoms include reduced tuber
number and size, misshapen tubers and
black scurf.
Research has shown tubers are more
susceptible to rhizoctonia when planted
in soil below 55 degrees Fahrenheit.
Phillip Wharton, associate professor
at the Aberdeen Research and Extension
Center, said in-furrow applications
to protect seed from disease include
Quadris, Elatus, Ridomil Gold 4SL and
Moncut. Seed treatments include Maxim
MZ, Maxim 4FS, Bark PST, Moncoat MZ
and Cruiser Maxx. Seed treatments are
targeted to control fusarium seed piece
decay and sprout rot.
Late blight is not common in Idaho,
but if it does occur, he recommended
use of a seed treatment with Mancozeb,
such as Maxim MZ or Moncoat MZ.
Another disease, Fusarium dry rot,
is the main cause of seed piece decay
and sprout rot in Idaho, Wharton said.
He suggested storing potato seed at 37
to 39 Fahrenheit because fusarium is
dormant at those temperatures.
When seed is received in spring,
check for signs of damage in transit, like
odors and liquefaction, he advised.
" After careful unloading, store the
seed at 40 to 42 degrees Fahrenheit
and 85 to 90% relative humidity and
keep it well ventilated, " Wharton said.
" When cutting seed, clean and disinfect
cutting equipment, preferably daily and
definitely between seed lots. "
Both Wharton and Woodhall
encouraged growers to have their soil
tested for pathogens at the university's
research centers. Wharton said to make
sure to get the correct depth for soil
samples. For example, pathogens that
cause black dot are usually in the top
3 inches of soil, while nematodes are a
foot deep.
" Soil tests are useful for troubleshooting
persistent issues, " Woodhall said.

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April 2020

Table of Contents for the Digital Edition of April 2020