My responses to proposed DPR actions and regulations on soil fumigants, particularly as they involve

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My responses to proposed DPR actions and
regulations on soil fumigants, particularly as
they involve perennial crops

• Michael McKenry
• UC Riverside

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Abstract

• The impact of soil moisture content on movement
  of true fumigants has been reported as an
  important determinant of performance since the
  early 60s (Goring, 1962).
• Quantification of its impact was reported
  throughout the 70s (McKenry, 1974 and 1976).
• In 1995 DPR decided to reduce off-gassing by
  implementing Township caps, reduced the total
  applied to 332lb/ac and required higher
  pre-irrigation moisture levels above the delivery
  outlets.
• Tree and vine growers, particularly in years with
  minimal fall rains, who follow these regulations
  are receiving poor fumigations when it comes to
  nematode control.
• Proposed regulations calling for water
  applications prior to and following the
  fumigation will also result in reduced nematode
  control, but it is the pre-treatment moisture
  requirement that results in poorest dispersal of
  the fumigants and could result in greater VOCs.
• There are better ways to reduce VOCs that
  involve shank design and soil prep.

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The assumption that 100 of the soil fumigant
inventory will become VOCs is absolutely
baseless.

• This means that in 2006 when DPR calculated 3
  of all VOCs were coming from soil fumigants they
  publicly overstated the case. The actual emission
  percentage for true soil fumigants is probably
  closer to 1 of all VOCs. The more persistent
  products and those with least affinity for water
  will have higher emission percentages.

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1, 3-D

• Soon after an application, 3 of the 1, 3-D
  applied is available for dispersal via soil air
  spaces and therefore available for emission.
  Meanwhile, half the remaining 1,3-D is held
  within soil water films and the other half
  temporarily sorbed onto soil particles. While in
  the water phase the degradation rate for cis 1,
  3-D is 25 / day at 25C or roughly 12.5 of
  cis-1, 3-D is hydrolyzed every 24 hr.

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Thus, 332 lb/ac of 1, 3-D placed 18 beneath a
concrete slab will hydrolyze to become 291 lb/ac
1 day after treatment and then12.5 of that
amount hydrolyzed to become 255 lb/ac at the end
of day 2. Not only is the fumigant buried, it is
degrading within soil.
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Hydrolysis means it is no longer 1, 3-D and no
longer volatile

• At 15C the degradation rate is 12 / day of the
  sorbed amount which 6 of the total remaining
  1, 3-D.
• At 5C the degradation rate is 4 / day which 2
  of the total remaining 1, 3-D.
• The hydrolysis rate for trans-1, 3-D is slightly
  slower than for the cis-isomer.

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(220 lb/ac 1,3-D)
(10)
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I have just shown you that fumigants have varying
rates of degradation and that

• EDB for example was applied at 1/5th the
  treatment rate of 1, 3-D but on day10 had more
  killing power in the soil than 1, 3-D.
• EDB has a degradation rate closer to 3 / day

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(23)
(15)
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You have now observed that

• Soil moisture content can greatly impact fumigant
  dispersal.
• By the way, for this silty clay loam soil
• field capacity is 24,
• ½ of field capacity is 17 and
• permanent wilting point is 10

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What concentration of each fumigant is required
to kill various soil pests at various
temperatures after 24 hours of exposure?

• We will refer to this concentration x time value
  as ppm days or ug/ml in soil water. All soil
  pests are essentially covered with films of water.

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If 23 ug/ml cis or 45 ug/ml trans 1, 3-D are
adequate to provide a 1X kill level of root-knot
nematode juveniles. What about other organisms
or life stages?
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Fig 3. An Hesperia sandy loam near Parlier
treated with 330 lb/ac 1, 3-D at 12 depth with
shanks spaced 18 apart in soil where moisture
content exceeded 12. Note that the value of
fumigation did not reach the 3 foot depth.
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Fig 4. A Hanford sandy loam near Parlier treated
with 330 lb/ac 1, 3-D at 12depth. Site I
received 2.5 water at 24 hr pre-treatment. Site
II received ½ at 1 hr post-treatment. Site III
received 2.5 between 1 and 2 days post treat.
Site IV was never irrigated but demonstrates deep
soil moisture content. Soil moisture values
determined 7 days after applic.
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A closer analysis of data presented on the
previous slide, including the change in moisture
content and nematode control. These are the
impacts of wetting a deep-dried soil, not a moist
one.
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Fig 10.
330 lb/ac 1,3-D
625 lb/ac 1,3-D
1400 lb/ac 1,3-D
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What is wrong with Field Capacity measurements?

• DPR wants them collected at the point of
  injection. This is a way to make sure there is
  plenty of moisture in the soil.
• 1) A moisture retention curve is needed for each
  soil type. Ten acres can have several soil types
  which places all decision-making in the hands of
  ag commissioners.
• 2) Measurements of FC are ambiguous! Use soil
  moisture content for less ambiguity and as a
  means to encourage dry soil.
• 3) It has to be even wetter above the measurement
  point to achieve their required moisture
  measurement.
• 4) Soils with high moisture that are then sliced
  with a shank could increase VOC emissions if the
  fumigant has persistence.
• 5) It is better to deep rip and deep dry the soil
  so that fumigants have somewhere to move besides
  upward.

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For tree and vine growers

• Get rid of the pre-treatment irrigations because
  particularly in a dry fall there begins to be
  chaos.
• The ground has been ripped, these growers do not
  usually have sprinklers and many growers are
  trying to flash their irrigation across the field
  surface using small furrows.
• To get rid of these requirements tree and vine
  growers need to separate themselves from the
  other growers by injecting deeper with proper
  shanks. They must convince EPA and DPR to change
  the 1995-96 DPR ruling on pre-treatment moisture.

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We have looked at fumigant movement, now lets
look at nematode control

• The following slides depict nematode control at
  each of 5 depths at 30 to 90 days after
  treatment. It begins with a soil having less than
  6 soil moisture from the Kearney Ag Center and
  moves to soils that hold higher moisture content.
• Note that one can find many data sets that
  include nematode kill and plant growth following
  different fumigations at Kearney. Refer to them
  in the on-line text entitled The Replant Problem
  and its Management.
• www.uckac.edu/nematode

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Fumigating finer-textured, high moisture content
soils, specifically at 12 to 19 H20

• Studies published in Proceedings of 2003MBAO
  Journal

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Then we developed the new Buessing shank
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Conclusions

• For tree and vine settings there must be
• 1) Attention to soil moisture content in down
  to 5 feet (to determine worthiness of fumigation
  and the need for additional Pic or MI).
  Equipment needed includes a microwave, scales and
  auger.
• 2) Buessing shanks with delivery at 28 and 18- 20
  inch depths. (this will reduce VOCs)
• 3) Pre-treatment ripping to 4 foot or even 5 foot
  in finer-textured soils. (this will reduce VOCs)
• 4) From an efficacy standpoint growers could live
  with post treatment irrigations properly timed
  that also delivered metam sodium, but not
  pre-treatment irrigations. Post treatment
  irrigations are primarily a problem because of
  handling issues.
• 5) Deep ripping and Buessing shanks may
  substitute for post treatment irrigations.

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Footnote 1

• The new parabolic design shanks that reach 30
  inch depth are 50 wider than old shanks and thus
  will leave a larger chimney trace in sandy loam
  soils than the old shanks. The impact of these
  shanks is most easily identified by insertion of
  a pointed rod into the soil as you attempt to
  find the shank chimney

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Footnote 2

• In reality, since 1996 growers of tree and vine
  crops have been waiting for fall rains or
  irrigated their fields prior to fumigation to
  satisfy local requirements. These growers do not
  have sprinklers and they may have ripped their
  fields from 28 to 72 inches deep ahead of the
  fumigation. To meet local requirements and an
  ambiguous label they have been furrow-irrigating
  across this land to be treated. The next slide is
  one of many examples of first year tree growth
  after such soil preparations ahead of 332lb/ac
  Telone II.

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With results like this, why fumigate?
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Footnote 3

• What has been demonstrated here with 1, 3-D also
  applies to a greater or lesser degree to other
  true fumigants including chloropicrin which
  degrades faster in warm soils and iodomethane
  which apparently degrades slower.