September/October 2020 - 23

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All in all, phosphites seem have a lot to offer, as do
many other products in the same 'biostimulant'
class. But how do they work?
Researchers around the world are undertaking
detailed studies to better understand the phosphite
mode of action. As already mentioned, phosphite
can exert toxic effects on certain pathogens. As well
as P. infestans, successful trials have also been seen
in control of Microdochium nivale in turfgrass. But
against true fungal diseases, like Septoria in wheat,
there's no evidence of fungicidal activity.
As for its fertilizing qualities - applications of
phosphite have been shown to enhance root growth
by as much as 50 per cent in a variety of crops - this
is a bit of a mystery, as we know plants can't convert
phosphite into accessible phosphate. It's led to a
flurry of activity amongst plant biologists in a race
to identify exactly what mechanisms phosphites
employ within the plant.
It also places phosphite products in something of
a gray area. Practically, they're registered either as
fungicides or fertilizers, yet technically they're not
true examples of either class. That's why both in
the U.S. and E.U., lawmakers are working towards a
proper classification of biostimulants: products that
optimize the metabolic efficiency of plants, in order
to increase yield, quality and overall plant health.
For growers too, the current lack of official
recognition for biostimulants such as phosphite can
cause problems, because as the law stands now, a
product must be registered as either a pesticide or
a fertilizer. Meanwhile firm evidence of performance
in the field will really start to help growers feel
more confident about adopting biostimulants as a
valuable part of their integrated crop management
programs.
Several studies have already demonstrated how
phosphites are at least as effective as conventional
contact fungicides such as mancozeb and
chlorothalonil, while work continues to confirm
a protecting effect against late blight seen in
phosphite-treated potato crops when applied in
conjunction with chlorothalonil.
Coming back to those Swedish results, one
particular point of interest stands out. Treatment
of late blight with a program combining fungicide
(in this case, cyazofamid) and phosphite was
applied at a 14-day interval and provided the same
performance as a 7-day application interval. Imagine
the benefits to be enjoyed from halving both
your fungicide bill and the number of application
passes through your potato fields. Backing up
such a strategy with a suitable decision support
system, to allow growers to have confidence in
their dosing decisions, could make a very valuable
contribution towards a more effective integrated
crop management program.
What's more, other studies are showing further
beneficial effects from phosphite applications to
potato crops. An Argentine study, published in
the American Journal of Plant Sciences, reported
that application of potassium phosphite to seed
tubers not only reduced the time between planting
and emergence but also stimulated early growth.
This was because the phosphite increased the
mycorrhizal colonization of the tubers. There's
also early evidence that phosphite can help in
defending crops against another disease caused by
a Phytophthora pathogen, in this case the 'pink rot'
brought about by P. erythroseptica.
This is a fast-moving area, especially as new details
on phosphite's capabilities and mechanisms
continue to emerge, as does legislation and
the regulatory environment for biostimulants.
Our current phosphite product, Cell Power®
Phorcephite®
, enjoys full U.S. registration as a
systemic fungicide for the control of downy mildew,
Pythium, Phytophthora and other diseases in a
range of crops, with a zero-day harvest interval. It's
a product we'll continue to develop, aided by our
own research as well as that of others.
So if you're not yet a member of the phosphite club,
perhaps the 2021 season will be your time to join?
Learn more at www.omexusa.com.
The product names and brands referenced
here are registered and trademarks of OMEX®
Agrifluids, Inc.
© OMEX® Agrifluids, Inc. 2020.
http://www.omexusa.com
September/October 2020

Table of Contents for the Digital Edition of September/October 2020
