Mar_Apr_PCC_2017_Web

BERRIES
Photo Credit: Mark Bolda
Exploring Biological Fungicides as an
Alternative to Methyl Bromide Fumigation
Page 10 Progressive Crop Consultant March/April 2017
Mark Bolda
UCCE Farm Advisor,
Santa Cruz County
With the recent prohibition of the
fumigant methyl bromide for preplant
soil disinfestation, California berry
growers face very real challenges to their
customary profitable crops of strawberries
and caneberries in the years to come.
The disease complex formerly controlled
by methyl bromide is creating trouble for
these cropping systems. The well-known
and widespread diseases caused by Verticillium
and Phytophthora are now being
joined in recent years by the pathogens
Fusarium and Macrophomina. The threat
to California berries, both actual and
potential, is not insignificant.
While a decent amount of research has
been done on methyl bromide alternatives
such as formulations of chloropicrin
and the yet to be registered Dominus (allyl
isothiocyanate also known by some as
“mustard seed oil”), the challenging mix
of diseases currently in place means that
researchers in the field must be considering
all the options and in particular will
benefit by investigating an integration of
solutions and methods.
When we speak of integrating solutions,
we are talking about using materials
and methods alongside the methyl
bromide chemical fumigant alternatives.
Some researchers have found promise
with the use of a fumigant alternative
followed by the incorporation of soil
amendments such as rice bran, mustard
seed meal or crushed crab shells, while
others see success with the application of
various mixtures of compost.
Another area which has garnered more
than a little interest for the post methyl
bromide era in the berry farming community
has been that of using of biological
fungicides. A biological fungicide
is a formulation of organisms such as
bacteria or fungi which can offer benefit
to the plants and the soils around them.
While many different modes of actions to
generate this benefit for these materials
are claimed, in the main these organisms
theoretically colonize the plant’s roots
and the soil around them, facilitating the
plant uptake of nutrients and in some
cases offer a measure of root protection
against pathogens by either competitively
excluding pathogens or actively suppressing
them.
UC Cooperative Extension in Santa
Cruz County has not been idle over the
past few years and has taken a very hard
look at a number of these biological
fungicides in the field, either when used
alone and in combination. These materials
included formulations of Trichoderma
asperellum and Trichoderma gamsii,
bacteria such as Bacillus subtilis, Bacillus
amyloliquefaciens, the actinobacterium
Streptomyces lydicus and we have tested
them both as plant dips as well as in season
drip tape applications.
The first trial in 2012-13 was run in an
organic field well infested with both Verticillium
and Macrophomina, and tested
a slate of biological fungicides, including
Serenade, Double Nickel 55, Actinovate,
Soilguard, Biotam and a group of
formulations from the Tainio company.
Transplants were initially dipped in
suspension of water and the product for
a few minutes and then held overnight,
ostensibly to allow the biological fungicide
to establish itself, and then planted
the next day. In most cases, follow up applications
of the same biological fungicide
were injected through the drip system
on a monthly basis after planting. The
reason for monthly applications through
the drip tape shared with me by manufacturers
and distributors has been that these
biologicals do not establish themselves
very well in the soil and hence need to be
augmented from time to time.
In this first test done in 2012-13, a
number of materials clearly had an effect