Spudman March 2023 - 18

Solubility of Herbicides Labeled for Use in Potato
Water solubility
Herbicide ppm (pH 7 25° C)
Veinal chlorosis after preemergence
application of metribuzin at labeled
rate, followed by 3 inches of simulated
excess rainfall. Russet Burbank is typically
tolerant and does not usually have this
symptom after application, so the excess
rainfall may have made the herbicide
more readily available for uptake. The
plants grew out of the injury, and there
was no loss in yield or quality.
used to simulate 3 inches and 6 inches
of additional rainfall over the two weeks
following application.
Four different herbicides labeled for
potatoes were used: Outlook, Matrix,
metribuzin and Prowl H2O. Since most
of the field calls involved some kind of
russet, these trials were conducted with
Russet Burbank.
The results were revealing. In
addition to stubby roots, Prowl H2O
caused interesting symptoms where
roots were twisted or bent at right
angles. Potato leaves in the Outlook
plus excess rainfall plots were unusually
crimped with a drawstring appearance.
Russet Burbank usually tolerates
metribuzin really well (unlike varieties
such as Shepody), but there was a lot
more injury from that herbicide plus
the excess rainfall than is normally seen.
Symptoms included veinal chlorosis.
Aside from the symptoms from
metribuzin on less tolerant varieties,
there wasn't a particular pairing of
variety to herbicide that really stood
out to Hutchinson, especially since
all these herbicides are labeled for use
in potatoes.
SOLUBILITY MATTERS
The solubility of herbicides is having
a significant impact on how and why
18
Spudman * March 2023
Matrix .................................. 7,300
Metribuzin .........................1,220
Outlook ................................. 1,174
Sulfentrazone.................... 780
Dual Magnum ...................488
Eptam ......................................370
Lorox/Linex ...............................81
Reflex ......................................... 50
Zidua ..............................................3.49
Chateau .........................................1.78
Sonalan ........................................ 0.3
Treflan ........................................... 0.3
Prowl H2O ................................. 0.2
The greater the value (ppm) relative to that
of the other herbicides, the more soluble
pH 7.5 160,000
Solubility, high to low
Sulfentrazone, Matrix, Metribuzin,
Outlook > Dual Magnum, Eptam
> Linex, Reflex > Zidua, Chateau,
Sonalan, Treflan, Prowl H2O
What happened to these herbicides
after the rainfall in May?
Depending upon soil characteristics, the
more soluble the herbicide, the more
available it is for uptake, and the further
it can move down in the soil profile
Image: University of Idaho
herbicide damage happens. Matrix
and metribuzin, the more soluble
herbicides, are already known for
moving down in the soil, so the excess
rain is causing even more problems.
Injury from Outlook, which is less
soluble, and Prowl H2O, which has
very low solubility, was the surprise,
but now makes some sense with the
high amount of rainfall soon after
application. Herbicides can be more
available for uptake. Unfortunately,
however, these herbicides can move
too far down below where the weeds
are germinating. In a situation like
this, there is now herbicide damage
and weeds.
Although it's hard to predict weather,
there are a few different herbicide
options, said Hutchinson, that can
lessen the possibility of herbicide
damage and provide consistent weed
control. Especially for farms on sandier
soils, it might be better to move away
from the most soluble herbicides and
still get good weed control. The most
soluble are Matrix, metribuzin, followed
by Outlook, Dual Magnum and Eptam.
The least soluble would be Reflex,
Zidua, Linex, Chateau and Prowl H2O.
However, injury might still occur when
that excess rainfall happens, even after
the least soluble herbicides are applied.
CONTINUED RESEARCH
It's difficult to put a dollar figure
on what this might cost the industry.
Hutchinson suspects that there is
more injury than expected since the
symptoms are not typical. But, when
potatoes are stressed, there is usually
a variety of contributing factors that
cause injury, such as excessive heat,
high water, nutrient deficiencies, etc.
" And it's not always herbicide damage,
so I like going out to a field to just hold
down the fear that growers are going to
lose yield, " Hutchinson said. " My job is
to identify what's going on - and that's
how this research is important - then
help growers figure out what to do this
season right away, through the summer
and maybe the fall, and for the next
time they're planting potatoes. "
Sometimes growers anticipate yield
loss due to herbicide injury, but so far
research hasn't concluded that.
" Be ready to control the weeds that
break through the initial application.
Take care of the injured potato crop,
don't let off on needed inputs, " said
Hutchinson. " The rain will stop, the sun
will come out, and farmers can still get
good yield and quality. "
The plan is to run the experiments
again this year, hopefully with funding
from the Northwest Potato Research
Consortium, because Hutchinson not
only wants to look at injury symptoms,
but also take soil samples to see how far
down the herbicides moved in relation
to the sprouts that are coming up and
the potato's roots.
" That'll put it all together to get
the total picture of what's going on, "
Hutchinson said.
Spudman March 2023

Table of Contents for the Digital Edition of Spudman March 2023
