Telone
is the most likely replacement for methyl bromide at the moment,
but several other compounds also are showing promise, according
to a University of Florida research team.
Since Telone is considered
to be the most likely replacement for methyl bromide in the near
future, the research team has been looking at ways to improve its
efficacy and consistency of performance.
In commercial trials,
there has been significant emphasis on broadcast applications of
Telone C-35 as a means of reducing worker exposure and the impact
of personal protective equipment (PPE) requirements, the research
team said. In most situations, the broadcast approach has worked
well.
“Over the past
three years, we have conducted a study investigating the relative
efficacy of Telone C-35 when applied broadcast versus in the bed
and the impact of additional chloropicrin applied at the time of
bed formation,” the team wrote. “We have determined
that under conditions of moderate disease pressure, Telone C-35
applied in the bed is more efficacious than (when) broadcast…”
Application of additional
chloropicrin in the bed following broadcast Telone C-35 improves
both soilborne disease and nematode control, they added.
Tillam plus Devrinol
for weed control were included in this study with all applications
of Telone II and Telone C-35, the researchers noted. Even with herbicide,
in-bed Telone C-35 provided better nutsedge control than any broadcast
Telone treatment. Adding chloropicrin back into the bed following
broadcast Telone II or Telone C-35 also improved nutsedge control.
“Tomato marketable
fruit production followed the same trend,” the research report
emphasized. “Methyl bromide was included as a grower standard
and Telone C-35, in-bed with Tillam plus Devrinol applied broadcast,
provided soilborne pest control and tomato yield equal to methyl
bromide.”
Recent changes in the
PPE requirements and Telone product setbacks have eased the impacts
of those issues for growers wishing to make in-bed applications,
the report pointed out. Hence, the feeling is there will be less
interest in broadcast applications, even though there are very real
benefits that should be considered.
“The take home
message for a grower is, if you are going to apply Telone C-35 broadcast,
you should apply another 125 to 150 pounds of chloropicrin per treated
acre in the bed,” the report read.
While time has been spent
fine tuning how to best use Telone C-35, the researchers continue
their search for new compounds as well as older products that may
have value for soil fumigation in preparation for tomato crops.
The group has conducted four large experiments over the past two
years. Twenty-four treatments were evaluated in 2001 and an additional
18 in 2002. As a result of these experiments, one success story
is fosthiazate. Registration for this material is being pursued
by Syngenta, and the combination of chloropicrin chiseled into the
bed and fosthiazate applied through the drip irrigation system is
considered “one of the best treatments for soilborne diseases
and nematodes” in these experiments.
Another promising product
is sodium azide, according to the team. Sodium azide has been around
for over 30 years and was first investigated as a soil fumigant
by PPG Industries in the early to mid-1970s. At that time it was
formulated as a granular product and showed great promise. It was
later shelved because methyl bromide was firmly entrenched in the
market place and azide also had some associated risks. Today, it
is available for research purposes as a liquid preparation.
“We have investigated
two application procedures: spray it on the soil surface and incorporate
in with a rototill and apply it through the drip irrigation system,”
the report explained. “Drip application is preferable because
it reduces potential worker exposure, but drip brings with it problems
we have discussed before about the uneven distribution of water
soluble products in sandy soils.”
In a trial on a commercial
farm near Immokalee, sodium azide provided better control of Fusarium
crown rot than methyl bromide, the team pointed out. It has performed
well for control of Fusarium wilt race 3 in trials in Manatee
County; however, results have not always been consistent. Nutsedge
control has been good in some trials and poor in others, including
trials with crops other than tomatoes. Some formulation changes
have occurred which seem to have improved performance. Spray-rototill
application has not been as effective as drip application.
Multiguard Protect:
The team also has been looking at a new product from South Africa,
trade named Multiguard Protect. This product is a contact nematicide
and is being marketed in South Africa for tomatoes. While the Florida
studies have produced mixed results, that may be due, in part, to
difficulty with distributing it uniformly across the bed, the team
said.
“One interesting
aspect of this product is the crop safety which allows applications
during the season,” the report read. “This would allow
it to fit in both a first crop as well as a double crop or be used
as a rescue treatment, if we can improve the efficacy and consistency
in our sandy soils.”
Since both Vapam
and K-Pam provide nutsedge control, they were included
in the team’s research trials. Nutsedge control is not possible
with most other alternative fumigants.
“We have seen improvement
in efficacy and consistency as a result of research we conducted
in the past three years to determine the movement of water soluble
pesticides in soil water as a result of drip irrigation application,”
the researchers wrote. “One promising treatment is the combination
of Vapam or K-Pam with either chloropicrin or Telone C-35. Vapam/K-Pam
would be delivered through the drip tubing in this combination.”
Inline,
the emulsifiable concentrate form of Telone C-35 has been included
in some research, and results have been mixed—again due to
drip delivery problems. The team has made some improvements and
continues to work at coming up with more.
“Probably the real
place for Inline is in double cropping as a supplemental treatment
just prior to planting the double crop,” the researchers said.
“One of the big
concerns with alternatives to methyl bromide is the potential impact
of the alternative on residual soilborne pest levels,” the
researchers pointed out, warning that this is particularly important
for double cropping. “The five-year study we just completed
did a lot to address growers’ concerns about the potential
for buildup following Telone C-17, methyl bromide and soil solarization.
