1Water Management Research Unit, USDA-ARS, Parlier, CA

2Department of Plant Sciences, University of California, Davis, CA

Effects of fumigants on target and non-target

organisms in soil

Recovery of beneficial soil microorganisms

after fumigation

For the past few decades, soil fumigants have been extensively

used to control target soil borne pathogens and weeds.

After methyl bromide phase out, alternatives such as 1, 3

dichloropropene (1, 3-D), methyl isothiocyanate (MITC),

chloropicrin (CP), dimethyl disulfide (DMDS) is increasingly

used.

Effect on non-target soil organisms are largely unknown.

Toxic only to the target organisms.

Biodegradable

Should not leach into the groundwater

A methyl bromide replacement candidate.

Ubiquitous, simple, and natural product.

Key component of biogenic atmospheric cycle.

Registered with FDA as a food additive.

Zero ozone depletion potential, a broad spectrum fumigant.

Critical role in sustaining the health of soil systems

Significant component of nutrient cycling

Changes in soil quality

Soil microorganisms, as a sensitive indicators of soil health.

Very little ecotoxicological information available for chemical alternatives to methyl bromide.

Important to gain broad biocidal activity.

Determine the effects and recovery of target and

non-target organisms under different fumigation

treatments and,

Compare these organisms in fumigated vs. non-

fumigated control sites

Traditionally a time consuming

task

Culturing techniques

Culture-independent method

Essential components of every living cell

Great structural diversity with high biological specificity

A proxy for the ‘living’ and ‘active’ microbial biomass

Not found in storage products

Relatively constant proportion of

the biomass

Laboratory Analysis

- Fatty acids extracted from

soil samples

- An Agilent 6890 gas

chromatograph

- MIDI Sherlock software

Signature PLFAs

Group Signature PLFAs

Actinomycetes 10Me16:0, 10Me18:0

Gram - bacteria cy17:0, 18:1w7c

Gram + bacteria i15:0, i16:0

Fungi 18:2w6c

AMF 16:1w5c

CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH ω-6 cis, cis-Δ6, Δ9 C18:2

Treatment † Application rates

(gal/acre) Tarp† Application method

Control 0 Bare -

Telone C35 (TFNB) 48 Bare Shank with N2 delivery

Telone C35 (TFNPE 48 PE Shank with N2 delivery

Telone C35 (T2/3NB) 32 Bare Shank with N2 delivery

Telone C35 (T2/3NPE) 32 PE Shank with N2 delivery

Telone C35 (T2/3NTIF) 32 TIF Shank with N2 delivery

Telone C35 (T2/3COTIF) 32 TIF Shank with CO2 delivery

MeBr:CP (MeBrPE) PE Shank

†Abbreviations: MeBr, Methyl bromide; PE, polyethylene film; TIF, totally impermeable film

Populations of Pythium spp. in soil samples collected from plots fumigated with MeBr PE (Methyl

bromide, PE tarp), T2/3COTIF (carbonated Telone C35, 2/3 rate, TIF tarp), T2/3 NB (Telone C35, 2/3

rate, bare), T2/3NPE (Telone C35, 2/3 rate, PE tarp), T2/3NTIF (Telone C35, 2/3 rate, TIF tarp), TFNB

(Telone C35, full rate, bare), TFNPE (Telone C35, full rate, PE tarp) liters per hectare. Error bar indicates

standard error.

Mycorrhizal PLFA from plots fumigated with MeBr PE (Methyl bromide, PE tarp), T2/3COTIF

(carbonated Telone C35, 2/3 rate, TIF tarp), T2/3 NB (Telone C35, 2/3 rate, bare), T2/3NPE (Telone C35,

2/3 rate, PE tarp), T2/3NTIF (Telone C35, 2/3 rate, TIF tarp), TFNB (Telone C35, full rate, bare), TFNPE

(Telone C35, full rate, PE tarp) liters per hectare. Error bar indicates standard error.

Vectors represent standardized canonical coefficients and indicate the relative contribution of each

biomarker group to each canonical variate

Important to know the recovery of non-target

soil organisms after fumigation.

Microplot test

DMDS was applied at 32, 64, 128,

or 256 mg a.i./L air space per vine.

Treatments were arranged in a

complete randomized block design.

Each treatment had six replicates.

Field Trial

Post-plant spot-fumigation was performed

to achieve 112, 224, 448, or 897 kg/ha.

The experiment was arranged in a complete

randomized block design. Each treatment

was replicated six times.

The ability of soil microorganisms improve after treatment with

pesticide is critical for the development of healthy soils.

Application of fumigants results in a decline of soil organisms.

Fungal and AMF biomass tends to significantly decrease in fumigated

soils.

Similar trend was observed for Gram negative and Gram positive

bacterial biomass.

Significant for management decisions as there are numerous benefits

of microorganisms in soil.

Examine the recovery of belowground component of the ecosystem.

Microbial community structure and soil structure redevelopment by

analysis of aggregate size distribution and aggregate stability with

different time frames;

Determine initial impact of different fumigants on both target and

non-target soil organisms; and

Compare the non-target organisms in fumigated vs. non-fumigated

control sites.

Thank you