Department of Pesticide Regulation

Environmental Monitoring and Pest Management Branch

1020 N Street, Room 161

Sacramento, CA 95814-5624



Study #160: Protocol for Sampling Phase Two Grape Management Practices

February 1997

I. INTRODUCTION

The Department of Pesticide Regulation (DPR) is conducting an educational and outreach program to mitigate movement of the preemergent herbicides simazine and diuron to ground water in Fresno and Tulare County grape vineyards. As part of this program, the University of California Cooperative Extension (UCCE) is conducting field studies in cooperation with DPR. The purpose of the vineyard studies are 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. Based on discussions with local grape growers and the Fresno area Biologically Integrated Viticulture System group, UCCE has suggested certain grape management practices to reduce or eliminate herbicide movement to ground water. DPR will perform deposition and soil sampling of selected treatments in this study to assess (a) herbicide application rates in support of UCCEs analysis of treatment efficacies, (b) to assess vertical and lateral herbicide movement in drip irrigation conditions, and (c) to evaluate potential ground water contamination risk from "as needed" drip chemigation applications of oryzalin, a substitute preemergent herbicide.

A. Furrow Irrigation

Irrigation water can serve as a vehicle for downward movement of herbicides, particularly in deep coarse soils where high infiltration rates and hydraulic conductivities may allow significant deep percolation. Coarse soils are common in many grape-growing regions of Fresno and Tulare Counties. Furrow and drip irrigation are two of the most common irrigation methods in local vineyards. Furrow irrigation percolation losses can be significant, particularly in coarse soils. A study of leaching under furrow, sprinkler, and basin irrigation methods (Troiano et al., 1990) found that for comparable water applications, both atrazine and inorganic tracer movement downward was greatest for the furrow irrigation method--when movement was measured directly under the furrow. UCCE has decided to evaluate the following treatments to reduce downward herbicide movement after late winter/early spring applications to grapes under furrow irrigated conditions.

FURROW IRRIGATION TREATMENTS

F1. Grower Standard Control: 2 lb simazine + 2 lb diuron per treated acre

F2. 1.5 lb simazine + 1.5 lb diuron per treated acre

F3. 1 lb simazine + 1 lb diuron per treated acre + simazine surfactant

F4. 1 lb glyphosate spot treatment, followed by delayed application of 1 lb simazine + 1 lb diuron per treated acre.

F5. Variable rate: 2 lb simazine + 2 lb diuron per treated acre at vine row; 1 lb simazine + 1 lb diuron per treated acre at furrow.

The strategy underlying all furrow treatments are similar: reduce herbicide use, particularly at those locations in space and time where irrigation water applications are most likely to result in deep percolation. Treatment F2 is a small reduction in use relative to the grower standard F1. Treatment F3 is a further reduction that also includes an organosilicon surfactant application. The addition of the surfactant is based on anecdotal reports of enhanced residual efficacy due to the presence of surfactant, and limited studies that suggest enhanced residual herbicide efficacy due to surfactant (Tan and Singh, 1996; Loveland Industries, unpublished data). Treatment F4 is also a reduced residual herbicide use treatment, but includes additional use of glyphosate. It is hoped that the glyphosate contact herbicide will successfully control weeds during early spring, thereby allowing later application of the residuals in an effort to avoid early spring rains and/or early irrigation applications under conditions of low early spring evapotranspiration (ET) conditions. Irrigations in the early spring are particularly susceptible to producing deep percolation due in part to low ET rates. Treatment F5 attempts weed control using a reduced rate application in the furrow where the downward flux of irrigation water is the greatest while maintaining the higher rate in the vine row.

UCCE applied these same furrow treatments in 1996 during the preliminary experimental phase of this study, and DPR conducted limited soil sampling (study #144). Time constraints precluded deposition samples in study 144, and interpretation of the weed control results and observational soil sampling results consequently suffered. This year, under the assumption that reduced herbicide use at the location and time of maximum water flux into the profile will reduce the net downward flux of herbicide relative to the grower standard, treatments A-F through E-F will be evaluated based solely on efficacy as measured by both comparative species-specific and overall weed counts conducted by UCCE. The only herbicide sampling by DPR in the furrow experiments will be deposition sampling to verify the herbicide application rates.



B. Drip Irrigation

A difficulty in evaluating downward movement of herbicides under the drip irrigation method is that the water application is not uniform over the surface of the field and, as a result, both water and herbicide may move downward, laterally, or both. In the study previously discussed (Troiano et al, 1990), an attempt was made to evaluate atrazine leaching directly under the drip emitters. Very little solute or tracer was recovered in cores taken below the drip emitters, even at the lowest level of irrigation (irrigation depth 0.75 ET calculated over entire plot area). This study concluded that "more frequent and detailed sampling of soil located from both beneath and between drip emitters is needed in order to adequately describe solute movement in low volume systems where horizontal movement to non-irrigated areas could occur." While drip is a low-volume irrigation method that should allow a high degree control over total water application and timing, it is possible that, relative to furrow irrigation, enhanced herbicide transport may occur under the drip emitters because of the water application is not spatially uniform. Further, computer modeling of herbicide transport under drip irrigation is not an alternative due to a lack of validated 3 dimensional variably saturated flow transport models. Therefore, field observations are needed to evaluate the downward and lateral movement of herbicide in coarse Fresno and Tulare County soils.

The following treatments have been selected by UCCE for studies in the drip irrigation sites.

DRIP TREATMENTS

D1. Grower standard control, fixed schedule irrigation. 2 lbs simazine + 2 lbs diuron per treated acre.

D2. Reduced variable rate application, fixed shedule irrigation. 1.5 lb simazine + 1.5 lb diuron per treated acre at vine row, 0.75 lb simazine + 0.75 lb diuron per treated acre in furrow.

D3. Reduced rate, oryzalin chemigation as needed, fixed schedule irrigation.

1.25 lb simazine + 1.25 lb diuron per treated acre, oryzalin applied through drip emitters as needed.

D4. Standard application, irrigation frequency based on historical ET.

2 lbs simazine + 2 lbs diuron per treated acre.

D5. Reduced variable rate application, historical ET-based irrigation.

1.5 lb simazine + 1.5 lb diuron per treated acre at vine row, 0.75 lb simazine + 0.75 lb diuron per treated acre in furrow.

D6. Reduced uniform rate, oryzalin chemigation, historical ET-based irrigation.

1.25 lb simazine + 1.25 lb diuron per treated acre, oryzalin applied through drip emitters as needed.

D7. Standard application, irrigation frequency based on current ET.

2 lbs simazine + 2 lbs diuron per treated acre.

D8. Reduced variable rate application, current ET-based irrigation.

1.5 lb simazine + 1.5 lb diuron per treated acre at vine row, 0.75 lb simazine + 0.75 lb diuron per treated acre in furrow.

D9. Reduced rate, oryzalin chemigation, current ET-based irrigation.

1.25 lb simazine + 1.25 lb diuron per treated acre, oryzalin applied through drip emitters as needed.

The treatments outlined above embrace 4 factors: rate (3 levels), placement (2 levels), oryzalin (2 levels), and ET (3 levels). Only 3 drip treatments will be monitored for soil distribution of herbicides by coring because (a) the number and design of treatment combinations is inadequate to isolate the factor effects due to potential interactions, and (b) DPRs analytical, sampling, and personnel resources are inadequate to sample all treatments. The treatments selected for monitoring in the drip experiments are D1, D6, and D7.

Irrigation water management is central to avoiding herbicide movement downward in the profile where organic carbon and biodegradation rates are low. Treatments D1 and D7 will allow a comparison of irrigation scheduling methods (fixed schedule vs. current ET-based irrigation scheduling). Treatment D6 will provide observational data on oryzalin movement under "as-needed" chemigation applications. Because of the uncertainty in lateral movement and herbicide distribution under drip irrigation conditions, these data are needed to document whether the substitution of oryzalin for simazine and diuron might pose a risk of ground water contamination under drip chemigation conditions.

II. OBJECTIVES

A. Furrow Irrigation

DPRs objective in the furrow irrigation experiment is to verify application rates of the various treatments in support of UCCEs analysis of treatment efficacy.

B. Drip Irrigation

DPRs objectives in the drip irrigation experiment are to (a) verify application rates of the various treatments in support of UCCEs analysis of treatment efficacy.

(b) compare the effect of current ET- and fixed-schedule irrigation regimes on downward movement of simazine,

(c) evaluate the lateral movement and between-emitter soil profile distribution of simazine under current ET- and fixed-schedule irrigation regimes, and

(d) obtain observational data on downward movement of oryzalin under "as-needed" drip chemigation applications.

III. PERSONNEL

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

Analyzing Laboratory: California Department of Food and Agriculture, Center for Analytical Chemistry

Authorship of the final report should include, but not be limited to, Frank Spurlock, Cindy Garretson, 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

A. Furrow Irrigation. Deposition samples will be taken in 4 furrow irrigation treatments: F1, F3, F4, F5. Each treatment will be replicated 4 times, 16 plots will be sampled for deposition of simazine and diuron.

1. Deposition samples - kimbies

a. treatments F1, F3, F4: measure deposition on 2 randomly located kimbies within each replicate plot, composite to 1 sample.

b. treatment F5: (i) at vine row: 2 randomly located kimbies on vine row center composited to 1 sample per replicate plot. (ii) in furrow bottom: 2 randomly located kimbies in middles composited to 1 sample per replicate plot

c. total number of furrow irrigation experiment deposition samples will be: F1, F3, F4 - (3 treatments x 4 plots x 1 sample per plot) + F5 - (1 treatment x 4 plots x 2 samples per plot) = 12 + 8 = 20 samples. Each sample is a composite of 2 kimbies. NOTE: Treatment F3 (spot application of glyphosate + delayed application of simazine and diuron) will be sampled for simazine and diuron deposition only; no glyphosate samples will be taken.

B. Drip Irrigation. Each of the nine drip treatments will be replicated four times. While deposition samples will be collected for all treatments (D1-D9) in support of UCs efficacy study, DPR will collect soil core samples only from all replicates of treatments D1, D7, and D6. The ET-based drip irrigation water application scheduling will be determined with the assistance of an irrigation consultant. Irrigation water application volumes to each treatment will be monitored using in-line flow meters; individual emitter flow rates will be checked. Bromide tracer will applied to treatments D1, D6, and D7. Soil coring and analysis for bromide will be conducted cooperatively with UCCE. The bromide results will be used to assist in determining when, and if, to analyze for herbicides in vineyard middles due to movement in lateral flow from drip lines. The following samples will be taken during the course of the experiment.

1. Background samples

a. water - 2 water samples from drip system - simazine, diuron

b. soil - Treatments D1, D6, D7. 3 treatments x 4 replicates x 1 sample per plot, where each sample = three 0-6" cores composited. Total soil background samples = 12 soil samples for simazine

2. Deposition samples

a. kimbies -

(i) treatments D1, D3, D4, D6, D7, and D9: measure deposition on 2 randomly located kimbies within each replicate plot, composite to 1 sample. 24 samples.

(ii) treatments D2, D5, D8: at vine row: 2 randomly located kimbies on vine row center composited to 1 sample per replicate plot. middles: 2 randomly located kimbies in middles composited to 1 sample per replicate plot. 24 samples

(iii) total drip irrigation deposition samples = 24 + 24 = 48 samples, each a composite of 2 kimbies.

b. oryzalin in drip water - 4 drip water samples during oryzalin application

3. Soil cores

Bromide tracer will be applied to the drip plots by UCCE. Periodic soil coring will be conducted in cooperation with UCCE to infer vertical and lateral water and bromide movement. Bromide analysis to be conducted cooperatively with UCCE. Bromide results will be used to determine when and if selected middles corings should be analyzed for herbicide.

a. short-term vertical simazine movement in response to current ET- and fixed schedule irrigations - treatments D1 and D7.

One 0-5 core x 6" increments taken approximately 7-10 days after initial irrigation directly under emitters. 2 treatments x 4 replicates x 1 core x 10 samples/core = 80 soil samples taken for simazine.

b. early season lateral simazine movement towards middles in response to current ET and fixed schedule irrigations - treatments D1 and D7.

One 0-5 core x 6" increments taken approximately 14 days after initial irrigation events, approximately 3 laterally from emitters. 2 treatments x 4 replicates x 1 core x 10 samples/core = 80 soil samples taken for simazine.

c. midseason oryzalin distribution in middles and under drip emitters - treatment D6.

Two 0-5 core x 12" increments taken 1 week after second oryzalin application. One core taken directly under emitter, one core taken approximately 3 laterally from drip line. 1 treatment x 4 replicates x 2 core x 5 samples/ core = 40 soil samples for oryzalin.

d. midseason simazine distribution in vineyard middles in response to current ET and fixed irrigation schedule treatments - treatments D1, D6 and D7.

One 0-5 core x 6" increments taken approximately 3-8 weeks after initial irrigation application and approximately 3 laterally from drip line. Samples to be split for bromide and simazine analysis. Simazine splits will be frozen until after bromide analysis. Presence of bromide, or lack thereof, will be used to determine whether simazine analysis is warranted for the individual treatments. The simazine 6" cores will be composited to yield 5 samples/core (12" increments). Actual sampling time dependent on rainfall and irrigation water applied. 3 treatments x 4 replicates x 1 core x 5 samples/ core = 60 samples for simazine.

4. 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

1. The total number of samples will be

a. soil background samples - 12 samples simazine

b. background water - 2 samples simazine/diuron

c. kimbie deposition - 68 samples simazine/diuron

d. applied drip water - 4 samples oryzalin

e. soil samples - 220 samples simazine

f. soil samples - 40 samples oryzalin

All samples will be analyzed by the California Food and Agriculture Analytical Chemistry Laboratory in Sacramento. Simazine in soil will be analyzed using the ELISA immuno-assay method, simazine/diuron deposition and background water samples will be analyzed using HPLC/UV-VIS, oryzalin water and soil samples will be analyzed using a method to be developed.

VI. DATA ANALYSIS

Normal-based statistical methods will be used to compare selected descriptors of simazine and bromide soil profile distributions for the fixed schedule and current ET drip water applications. These descriptors may include depth to 50% leaching, total solute mass recovered through the profile, or percent of application recovered in 0-5 depth. Simazine and bromide distributions may be compared to empirical models describing water infiltration and redistribution from point source applications. Descriptors of oryzalin soil profile distributions may be used to evaluate oryzalin mobility relative to simazine or bromide at equivalent water application rates. A comparison between 1-dimensional modeled oryzalin leaching profiles and actual depth profile below emitter may also be conducted.

LITERATURE CITED

Tan, S, and M. Singh. 1996. Weed control efficacy of diuron and norflurazon as affected by adjuvants. Submitted to Florida Agricultural Experiemntal Station.

Troiano, J, C. Garretson, C. Krauter, and J. Brownell. 1990. Atrazine leaching and its relation to percolation of water as influenced by three rates and four methods of irrigation water application. Pub. EH 90-7. Environmental Hazards Assessment Program, Calif. Dept of Food and Ag. State of California.