California Pepper Commission


California Pepper Commission Summer 2007 Powdery Mildew Project, Oxnard, California

California Pepper Commission Summer 2007 Powdery Mildew Project, Oxnard, California
Final Report
Prepared By: David Holden
Holden Research and Consulting
December 2007


In a randomized complete block design (RCBD) trial, nine different fungicide treatments were evaluated against an untreated check, to screen for efficacy against Powdery mildew (Leveillula taurica). Conditions in the field did not favor the development of this disease, but in the final analysis, though disease pressure was light, all products tested did show significant reduction in disease incidence and severity over the untreated check. All data rated as significant was done so utilizing the New Duncanís Multiple Test Range at a 95% confidence level.

Methods and Materials

Test Location: Oxnard, CA

Planting Date: May 2, 2007 Transplanted

Start Date: July 17, 2007

Harvest/Completion Date: October 4, 2007

Final Report Date: December 2007

Number of Treatments: Ten

Application Method: Solo Backpack airblast sprayer

Spray Volume: 100, 125, and 150 gal/acre

Treatment Timing: See Table 1 below.

Planting Density: Approximately 26,000 plants per acre

Data Collection: Incidence and severity of disease

Statistical Analysis: Duncanís Multiple Range Test (DMRT)

Plot Size: 10 feet (three beds) by 20 feet

Data Analysis Package: Gyllings Data Management Agricultural Research Management Software, Version 7.2

Discussion of Methods

This trial was laid out as a Random Complete Block Design (RCBD) of nine treatments and a water check control. Each treatment consisted of four replicates each measuring ten feet (three beds) by twenty feet in length. Data was collected from the center bed of the three beds utilizing the two outer beds as buffers. Treatments were applied in the morning. All treatments went on in the equivalent of 50, 100, and 150 gallons of water per acre. The following table shows the treatments and dates for each treatment called for in the original protocol.

Table 1: Treatments and schedule (A=July 17, B=July 30, C=August 16, and D=September 6, 2007)

Trt No.Treatment NameProduct RateProduct Rate UnitGrow StageAppl Code
1Untreated Check    
6Inspire (Syngenta)7FLOZ/APREHARABCD
7Inspire (Syngenta)7FLOZ/APREHARABCD
8Quadris (Syngenta)15.4FLOZ/APREHARABCD
10Milstop—Potassium Bicarbonate (Bioworks)2.5LB/APREHARVABCD

No deviations occurred from the above treatment schedule. All applications were applied as directed foliar treatments using a Solo Backpack Airblast Sprayer with a two line Gearmore Nozzle.

No phytotoxic effects to the peppers were ever observed from any of the treatments over the course of this trial.

Results and Discussion

The test area was managed for nutrients and pests in the same manner as the surrounding fields with the exception that no fungicides were applied to the test area, except for the test materials. The test area was monitored for pest development on a regular basis once treatments had begun. Evaluations for Powdery mildew were made by collecting ten leaves per replicate (forty leaves per treatment) and rating them for the presence of mycelia on the undersides of the leaves. Incidence percentage was based on the total number of leaves found with Powdery mildew divided by the total number of leaves evaluated per treatment. In turn the severity ratings were based on the average percent coverage of the undersides of the leaves found with mycelia. In other words a 10 percent severity rating would mean that the average amount of mycelia found per leaf on the underside of the infected leaves was 10 percent. Both average daily temperature and leaf wetness ratings were taken by this investigator utilizing an infield Watchdog data collector during the course of the trial and supplied to Dr. Michael Coffey for evaluation and correlation of disease development to a temperature/leaf wetness modeling system for disease development. Data from this monitoring will be interpreted and reported on by Dr. Coffey, but in season discussions with Dr. Coffey showed that the model predicted limited disease development pressure. This indeed was the case as will be seen in the following charts. One other evaluation was planned for this trial, but due to the limited disease development, it was not possible to perform. Loss of peppers from sunburn based on disease induced leaf drop was scheduled, but no leaf drop occurred in this trial.

Chart 1 shows the average incidence of Powdery mildew found per rating date by treatment, sorted from lowest overall average rating to the highest average incidence found. As can be seen in this chart, based on the average post treat incidence ratings (the last column), all tested materials provided significant control of Powdery mildew when compared to the untreated check. Though there was numerical separation of the materials, for degree of pest incidence, this was not found to be significant. Probably the most significant (not based on statistical analysis) information to be found was that at no time during the trial was any Powdery mildew found in the Cabrio, Inspire, Inspire/Revus, and Quadris treatments. As mentioned above disease development was limited with the final pre-harvest evaluation only showing about a 35 percent incidence of Powdery mildew for the untreated check.

Chart 2 shows the average severity for Powdery mildew development based on the evaluation methods mentioned above. This data was similar to the incidence data evaluations for the disease with the average in season severity of disease found to be significantly less for all treatments over the untreated check.

All data rated as significant was done so utilizing the New Duncanís Multiple Test Range at a 95% confidence level.


Though disease development pressure was light for this test site, the test did show that under these conditions all registered and future potential fungicides showed similar control of Powdery mildew. Under more severe conditions a better separation of these fungicides as to efficacy may be seen.

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