April 2020 - 26

active ingredient needed for disease
control. Multiple
applications
of
% Pink Rot - 2018 - Field Infection
relatively high rates are required for
phosphite fungicides to control pink rot
infections in potato roots and tubers.
Currently growers are advised to apply
up to a total of 30 pints per acre in a
season over three to six applications.
This has been the most effective
approach for varieties that are highly
susceptible to pink rot, such as Russet
Norkotah. The fungicide is taken up by
the plant and translocated to the tubers
where it provided protection against
pathogen infection.
Recent work from scientists in Canada
(Dr. Gefu Wang-Pruski and others)
showed that phosphite uptake in potato
plants increased for up to 52 hours after
application. From this research, the
question arose whether growers should
maximize the time between phosphite
fungicide application and irrigation to
maximize uptake.
In other words, should growers
wait 48 hours after application before
turning the pivot back on? Under the
semi-arid conditions present in many
potato growing regions, this would not
be difficult, if not impossible.
TRIALS
Field trials were conducted in 2018
and 2019 on Russet Norkotah to
evaluate the effect of interval between
phosphite
fungicide application and
irrigation. The trial area was infested
with the pink rot pathogen at planting
and again at hilling to increase disease
pressure.
Treatments included:
1. Untreated check (no fungicide)
2. 48-hour interval between fungicide
application and irrigation
3. 24-hour interval
4. 12-hour interval
5. Six-hour interval
Phosphite fungicide (Resist 57,
Actagro) was applied when the largest
tubers were dime-size (about 15
millimeters in diameter), and again
two more times using a two-week
interval between sprays for three total
applications.
In 2018, pink rot pressure was uniform
in the trial area. Phosphite fungicide
applications significantly reduced
pink rot incidence at harvest if the
26
Spudman.com
10
8
6
4
2
a
b
b
ab
b
UTC
48
24
12
6
Time between phosphite application and irrigation (hours)
Figure 2: Effect of interval between phosphite fungicide application and irrigation by center
pivot in 2018.
% Pink Rot - 2019 - Post-Harvest Challenge
100
80
60
40
20
a
b
c
c
c
UTC
48
24
12
6
Time between phosphite application and irrigation (hours)
Figure 3: Effect of interval between phosphite fungicide application and irrigation by center
pivot in 2019.
application was made at least 12 hours
prior to irrigation (Figure 2). Fungicide
applications made only six hours before
irrigation were statistically similar to
the untreated check, but also similar
to the other treatments. Application
intervals of 24 and 48 hours were no
more effective than applications made
at 12 or six hours pre-irrigation.
When the trial was repeated in 2019,
disease pressure was very low. Healthy
tubers were collected at harvest and
then
challenged with
the
pink
rot
pathogen. This is an effective method
to evaluate the uptake and protection
granted by phosphite-based fungicides
due to the systemic nature of the
fungicide. In 2019, the six-hour interval
treatment was not as effective as the
12-, 24-, or 48-hour interval treatments
(Figure 3). Similar to the 2018 field data,
no differences were observed among the
12, 24, and 48 hour interval treatments.
LONGER INTERVAL
PRE-IRRIGATION
Potato growers who are using
phosphite-based fungicides can
% Tubers with pink rot
% Tubers with pink rot

http://www.Spudman.com

April 2020

Table of Contents for the Digital Edition of April 2020