Study 152: Effect of Ground Cover on Dormant Spray Runoff from Orchards

California Department of Pesticide Regulation

Environmental Monitoring and Pest Management

1020 N Street, Room 161

Sacramento, CA 95814-5624

December 4, 1996

I. Introduction

In the San Joaquin Valley, the organophosphorus insecticides diazinon, chlorpyrifos, and methidathion are generally applied as a dormant spray on nut and stone fruit trees. Dormant spray washoff may occur after rainfalls, allowing these compounds to enter the San Joaquin River watershed and impact water quality (Ross 1992 and 1993). Previous studies by the Environmental Monitoring and Pest Management Branch regarding rain runoff from orchards after application of dormant sprays (Ross 1995, Ando 1996) indicated that some management practices, such as a ground cover of clover or a light soil incorporation, can reduce the amounts of dormant spray moved off site from a treated orchard. In this study, only the effect of native grasses and clover will be examined because soil incorporation is not an acceptable test treatment for the cooperating grower.

II. Objective

To determine if the total amount of diazinon washed off an orchard after winter rainfalls varies significantly with different ground covers in between the tree rows.

III. Personnel

This study will be conducted by personnel from the Environmental Hazards Assessment Program in the Environmental Monitoring and Pest Management Branch of the California Department of Pesticide Regulation. Study personnel include:

Project Leader: Heinz Biermann

Field Coordinator: Dave Kim

Senior Scientist: Lisa Ross

Chemist: Karen Hefner

Agency & Public Contact: Pat Dunn

All questions concerning this study should be directed to Pat Dunn at (916) 324-4077.

IV. Study Plan and Sampling Methods

Potential reduction in dormant spray runoff will be examined in one orchard cultivated with two types of vegetation in between the tree rows (i.e. row middles). A single treatment of dormant spray containing diazinon will be applied in accordance with label instructions. Uniformity of deposition between rows will be checked by Kimbie® sheets placed on the orchard floor.

Treatment rows in an orchard will be arranged in a completely randomized design. The two treatments are clover in the row middles and native grass in the row middles. The rows should be approximately equal in length and exhibit no slope perpendicular to the length of the row.

The volume of rain runoff from each treated row will be measured using 75-mm flumes equipped with a steel well, housing a pressure transducer. Each pressure transducer will be connected to a Campbell 21X datalogger to continuously monitor water height in the flume. Water height will be converted to volume using calculations experimentally determined by Clemmens et al. (1984). Water samples will be automatically collected as soon as water flow is detected in the flumes by the Campbell datalogger using an ISCO® automated water sampler operated with a 12 V external battery.

Application: A single treatment of diazinon will be applied. Deposition on the orchard floor will be estimated using absorbent fall-out sheets (Kimbies®) placed in the tree rows. Four Kimbies each will be placed in the eight treatment rows. Each fall-out sheet will be analyzed separately. Concentrations will be reported in mg per Kimbie® sheet.

Water Sampling: During two rain events after the application, water will be collected from each treatment row and analyzed for diazinon. Water will be collected at specific intervals, evenly spaced to cover the entire runoff event, whenever possible. The number of water samples required to cover each runoff period will vary depending on rain intensity and duration, field dimensions, soil type, etc. Whole water samples and filtered (0.7-m glass fiber filter) water samples will be analyzed. In addition, a back-up sample will be collected for each sample analyzed. Concentrations will be reported in g/L.

Meteorological Data: Temperature, humidity and rainfall will be collected at the site using a Met-One® Weather system and a Texas Instruments tipping rain bucket, respectively. Data will be recorded using a Campbell 21X datalogger operated with a 12 V external battery.

Total number of samples for chemical analysis (estimated):

Deposition: 8 treatment rows * 4 sheets per row = 32

Water, whole: 6 samples * 8 rows * 2 rain events = 96

Water, filtered: 6 samples * 8 rows * 2 rain events = 96

Quality Control: blind spikes and field blanks about 10% of total number of samples = 26

TOTAL = 250

V. Data Analysis

Runoff mass of diazinon in water will be expressed as total mass, and as a percent of the total amount applied (theoretical) or deposited (measured) on site. If applicable, water concentrations may be used in the analysis, too. Normalized mass values (either per unit area or application mass) will be used in the analysis of variance to determine if treatment differences exist.

VI. Chemical Analytical Methods and Quality Control

Chemical analysis will be performed by the California Department of Food and Agriculture Laboratory. The analysis method is the same as used in the previous study (Ross 1995) with the modification of using a 0.7-m glass fiber filter instead of a 0.45-m cellulose filter. Continuing quality control will be conducted in accordance with EHAP Standard Operating Procedures.

Soil texture and organic carbon will be determined in our Fresno facility. Soil texture will be determined using the hydrometer method (Bouyoucos 1962) and soil organic matter by dichromate reduction with silver sulfate (Rauschkolb 1980).

VII. Timetable

Field Location October to November, 1996

Equipment Purchases October to December, 1996

Field Preparation November 1996

Equipment Installation December 1996

Sample Collection January to March, 1997

Chemical Analysis January to April, 1997

Draft Report July, 1997

VIII. References

Ando, C. 1996. Investigation of Possible Management Practices to Reduce Dormant Spray Runoff for Soil Plots. EHAP Study 148.

Bouyoucos, G.J. 1962. Hydrometer method improved for making particle size analyses of soils. Agronomy J. 54:464-465.

Clemmens, A.J., M.G. Bos, A. Replogle. 1984..Portable RBC flumes for furrows and earthen channels. Trans. ASAE 27(4):1016-1020.

Rauschkolb, R.S. 1980. Soil analysis method S:18.0, Organic matter dichromate reduction. In: California Fertilizer Soil Testing Procedures Manual.

Ross, L.J. 1992. Preliminary results of the San Joaquin River study; Winter 1991-92. Memorandum to Kean Goh, Environmental Hazards Assessment Program, California Department of Pesticide Regulation, May 22, 1992.

Ross, L.J. 1993. Preliminary results of the San Joaquin River study; Winter 1992-93. Memorandum to Kean Goh, Environmental Hazards Assessment Program, California Department of Pesticide Regulation, Sept. 23, 1993.

Ross, L.J. 1995. Protocol for Reducing Dormant Spray Runoff From Orchards. EHAP Study 141.