September/October 2017

FUMIGATION ALTERNATIVES FOR TREE AND VINE CROPS
Are there novel materials for
soil fumigation?
Orchard fumigation rig (background) with soil sealing rig (foreground)
Photo Courtesy: Andrea Westphal
By: Andreas Westphal | Department of Nematology, University of California, Riverside, Kearney Agricultural Research and Extension center, Parlier, CA
By: Mike Stanghellini | Director of Research & Regulatory Affairs, TriCal Inc., Hollister, CA
Sustainability of many crops is put at
risk by the build-up of soil-borne
plant pathogens. While yield-reducing
effects of air-borne maladies can often
be effectively mitigated by pesticide
inputs, soil-borne problems are much
more challenging. By definition, pathogens
causing these diseases persist in the
complex environment of the soil matrix.
On the one hand, this complexity
increases the time that it takes for these
culprits to spread. On the other hand,
soil complexity renders suppression
of these pathogens and pests generally
more challenging than air-borne diseases
and pests. In fact, soil-borne maladies
are often the key components that
determine how frequently a crop or crop
group can be grown in specific fields.
These restrictions lay the foundation for
crop rotation programs. For example,
in nematode management, the use of
non-susceptible host plants of specific
nematode pests may be prescribed to
avoid the build-up of injurious nema-
tode populations. Such strategies can
be very effective when crops of similar
value and equipment requirements are
used. The situation becomes challenging
when high-value crops are produced
in highly specialized systems where a
diversion to less profitable crops is not
feasible, such as when high land rental
costs introduce additional economic factors
that come into play. In some cases,
limited crop rotation alternatives exist
because of the wide host range of pathogens
or pests. For example, root-knot
nematodes have very wide host ranges,
and a rotation based on various susceptible
vegetable crops would be unfit to
reduce infestation levels in fields.
Methyl Bromide
For decades, soil fumigation has
been used to reduce these important
crop-limiting pests by rendering pestfree
(or effectively managed) soil environments.
Since its registration in the
US in 1961, methyl bromide had been
an effective tool to reduce soil-borne
maladies. One main strength of methyl
bromide is its versatility under different
application conditions. Its high vapor
pressure coupled with a greater-than-air
density allowed methyl bromide to effectively
penetrate complex soil matrices
that differed considerably in temperature,
moisture level, and texture. Concerns
about methyl bromide’s ozone-depleting
potential in the stratosphere
led to its phase-out under the Montreal
Protocol. After its phase-out from
general use in the US in 2005, Critical
Use Exemptions (CUE) were granted for
selected applications where technical alternatives
were not available. This helped
protect against market disruptions in
strawberry and other high-value crop
industries in the US and other countries.
The 2016 growing season marked the
end of the CUE process in the United
States. For 2017 and future years, the
Continued on Page 18
16 Progressive Crop Consultant September/October 2017