The Department of Pesticide Regulation (DPR)
is conducting an educational and outreach program to mitigate
off-site movement of the preemergent herbicides simazine and diuron
from grape vineyards in Fresno and Tulare Counties. As part of
this program, the University of California Cooperative Extension
(UCCE) is conducting field studies in cooperation with DPR to
test different management practices for their ability to reduce
the downward movement of herbicides in coarse soils while maintaining
acceptable crop health and weed pest control. DPR will perform
sampling of soil in this study to assess the movement of simazine
after irrigation water application.
A. Furrow Irrigation
The objective in the furrow irrigation experiment
is to evaluate and provide observational data on simazine movement
under selected treatments.
B. Drip Irrigation
The objective in the drip irrigation experiment
is to compare the relative effect of selected treatments on downward
movement of simazine through the soil profile under drip irrigation
This study will be conducted by the Environmental
Hazards Assessment Program (EHAP) under the general direction
of Don Weaver, Senior Environmental Research Scientist. Key personnel
are listed below:
Project Leader: Frank Spurlock
Field Coordinator: Cindy Garretson
Senior Staff Scientist: John Troiano
Laboratory Liason: Nancy Miller
Experimental Design/Data Analysis: Terri
Authorship of the final report should include,
but not be limited to, Frank Spurlock, Cindy Garretson, Terri
Barry, and John Troiano. Questions concerning this monitoring
program should be directed to Peter Stoddard at (916) 324-4078,
facsimile (916) 324-4088.
IV. STUDY DESIGN
For these preliminary studies, a selected number
of the total experimental treatments planned by UCCE will be sampled
for movement of the herbicide simazine.
A. Furrow Irrigation.
In the flood irrigation experiment, seven treatment
plots (shown on plot map 1) will be sampled by DPR. The treatments
on these plots are listed below.
Treatment 1. 2 lb simazine ai/ac + 2 lb diuron ai/ac
Treatment 2. 1 lb simazine ai/ac + 1 lb diuron ai/ac + surfactant
Treatment 4. 1 lb simazine ai/ac + 1 lb diuron ai/ac + no surfactant
Treatment 6. Roundup 0.5 ai/ac as needed
The plots to be sampled are those closest to
the upstream, or headwater area of the furrow irrigation experiment
shown in plot map one. Treatment number six is a control to allow
measurement of carryover residue concentrations from previous
There will be one sampling event for the furrow
irrigation experiment. The plots marked on plot map one for treatments
1, 2, and 4 will be sampled by soil coring after the first irrigation
event. Two composite cores (5 foot cores in 6" increments)
for treatments 1, 2 and 4 will be taken at the approximate locations
shown in the plot map. Each composite core will be obtained from
compositing two individual soil cores. A single composite core
(from two individual cores) will be taken from each of the control
treatment plots (number 6).
The total number of soil samples to be analyzed
from the furrow experiment will be 120 (a. Plots for treatments
1, 2 and 4: 5 plots x 2 composite cores per plot x 10 discrete
samples per core = 100; plots for control treatment 6: 2 plots
x 1 composite core per plot x 10 samples per core = 20; 100 +
20 = 120).
B. Drip Irrigation.
Three selected treatments (Treatments 3, 4
and 5 on plot map 2) by three replicates will sampled by soil
coring in the drip irrigation experiment.
Treatment 3. Variable rate application: 1 lb ai/ac simazine + 1 lb ai/ac diuron
on vinerow and 2 lb ai/ac simazine + 2 lb ai/ac diuron to canopy edge;
16" x 30" fabric under emitters;
Treatment 4. Variable rate application as above; no fabric
Treatment 5. 2 lb ai/ac simazine + 2 lb ai/ac diuron applied from canopy
edge to canopy edge over berm
Each treatment plot in each block will be sampled
by taking single cores (0-5 feet in 6" increments) to yield
3 treatments x 3 blocks x 1 five foot composite core x 10 samples
per core = 90 soil samples. These soil cores will be taken after
the first drip irrigation event. Two cores (0-5 feet in 6"
increments) will also be taken for background samples outside
the study area. The total number of soil samples taken in the
drip irrigation experiment will be 90 + 20 = 110.
The total number of soil samples collected
will be 120 (furrow) + 110 (drip) = 230 samples. The soil samples
will be handled as provided in the following EHAP SOPS:
Collecting of Soil Cores with Bucket Augers
Transport and Storage of Soil Samples
V. CHEMICAL ANALYSIS / QUALITY CONTROL
Samples will be analyzed for simazine by California
Food and Agriculture Analytical Chemistry Laboratory in Sacramento
using the ELISA immuno-assay method; the detection limit is 15
ug kg soil-1.
The soil ELISA QA/QC procedures will consist of a matrix blank
plus two matrix spikes to be included with each extraction set.
Results from the matrix spikes will be evaluated to determine
if they fall within predetermined control limits.
Two cores from the furrow irrigation control
plots and two cores randomly selected from the drip irrigation
plots will be analyzed at DPR facilities in Fresno for particle
size analysis and organic carbon.
VI. DATA ANALYSIS
Each core will be evaluated for total simazine
recovered and depth of leaching by treatment. An additional comparison
of recovery and/or depth of leaching with late season residual
efficacy may also be possible.