California Pepper Commission


California Pepper Commission Summer 2008 Powdery Mildew Project, Ventura, California

California Pepper Commission Summer 2008 Powdery Mildew Project, Ventura, California
Final Report
Prepared By: David Holden
Holden Research and Consulting
January 2009


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 favor the development of this disease during the 2008 season in the Ventura growing area. Significant control of this disease was seen on average from eight of the nine tested products, with six products giving superior control of the disease over the other products and untreated check. All data rated as significant was done so utilizing the New Duncan's Multiple Test Range at a 95% confidence level.

Test Location: Ventura, CA

Planting Date: Early May 2008 Transplanted

Start Date: July 10, 2008

Harvest/Completion Date: Late September 2008

Final Report Date: January 2009

Number of Treatments: Ten

Application Method: Solo Backpack airblast sprayer

Spray Volume: 50 or 100 gal/acre

Treatment Timing: See Table 1 below.

Planting Density: Approximately 26,000 plants per acre

Data Collection: Incidence and severity of disease, along with estimated percent loss.

Statistical Analysis: Duncan's 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 or 100 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 18, B=July 29, C=August 14, and D=August 25, 2008)

Trt No.Treatment NameProduct Rate UnitProduct RateGrow StageAppl Code
1Untreated Check    
6Revus (Syngenta)7FLOZ/APREHARABCD
7Inspire (Syngenta)7FLOZ/APREHARABCD
8Quadris (Syngenta)15.4FLOZ/APREHARABCD
Bicarbonate (Bioworks)

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. In addition to disease evaluation, a sampling evaluation was conducted prior to harvest to determine if there were increased losses to marketable fruit due to leaf loss and increased sunburn of the fruit. All fruit from six plants per replicate was collected and evaluated for unmarketability due to damage from sunburn or sunburn induced rotting. This data is presented as percent loss due to sunburn/rot.

Chart 1 show 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), season long treatment with Rally, Quintec, Cabrio, Inspire, Quadris, and Flint gave significant control of Powdery mildew over Revus, Milstop, and the untreated check. DuPont LEM 17, Revus, and Milstop also performed significantly better than did the untreated check. The last evaluation column at 15 days after treatment D probably gives a clearer picture of the control showing the final rating levels for each of these treatments. As can be seen in the chart there was never any disease development seen in the Rally, Quintec, Cabrio, Inspire, or Quadris treatments while at the end of the trial virtually 100% of the untreated plants had crop destructing incidence of Powdery mildew.

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.

Chart 3 shows the percent estimated loss of fruit due to sunburn or rot from loss of shade providing leaves. Though there are numerical differences seen in these numbers, no significant differences were seen between any of the treatments and the untreated check. From a numerical perspective on average less loss was seen in the treatments that also showed no or little Powdery mildew development.

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


With heavy disease pressure development seen during the 2008 season in this test plot, the effectiveness of the tested products was well defined. It would appear that growers have numerous effective products either available or in the development stage for control of this disease for conventionally grown peppers. Due to certain label restrictions (number of applications, pre-harvest intervals, etc.) future studies would help to establish rotational product use regimes to provide information on how to use these chemistries effectively for the control of Powdery mildew.

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