Skip to main content Skip to navigation

Organic Acid Trial in Mature ‘Meeker’ Raspberry

Volume 6, Issue 6

Lead scientists: Lisa W. DeVetter (Assistant Professor of Small Fruit Horticulture at WSU-Mt. Vernon), Dave Bryla (Research Horticulturist at USDA-ARS, Corvallis), and Sean Watkinson (Scientific Assistant for the WSU Small Fruit Horticulture Program)

Acknowledgements: Chris Benedict (Whatcom County Extension) and Randy Honcoop (red raspberry grower cooperator in Lynden, WA)


The objective of this study was to evaluate the impact of organic acids on mature red raspberry grown in western Washington.


This trial was initiated in 2015 in a four-year old commercial field of ‘Meeker’ red raspberry grown in Whatcom County, Washington.  Treatments were applied in a conventionally managed field that was part of a larger trial comparing different fertilizer, cover cropping, and irrigation practices.  In this study, four treatments were compared and the experimental design was a completely randomized design with treatments replicated three times.  Plots in which the treatments were applied were single-row plots 17 feet in length with treatments applied on both sides of the row.  Treatments included: 1) organic acids (OA); 2) brassica seed meal (BSM); 3) organic acids plus brassica seed meals (OA+BSM); and 3) standard grower management practices (control; abbreviated STD).  The organic acid treatment was a commercial product (22% organic acids).  The brassica seed meal was Pescadaro Gold Mustard Meal (NPK 4.5-1.5-1.15) and was applied annually on the soil surface of the row at 1 ton/acre.

Organic acid treatment application began in April 2015 and the first application was applied in solution with water at 4 gallons/acre. Following this, the organic acid treatments were applied at 2 gallons/acre every other week until Sept. 1, 2015 (8 applications total).  In 2016, treatment applications were made in the same plots as 2015 and started in May.  The same rates and application schedule used in 2015 was followed in 2016 (applications made every other week; 8 applications total).  However, in order to promote movement of the product into the root zone, 60 gallons of water/plot were applied immediately after organic acid application.

Nutrient applications were not adjusted in any of the treatments and followed grower management practices.  Data collected include estimated yield through, average berry weight, leaf nutrient concentration, and soil chemistry.  A subset of those data are presented below for 2016.  Data were analyzed using RStudio (Version 0.98.1103 – © 2009-2014 RStudio, Inc.).  Assumptions of normality and unequal variance were corrected using transformations and data are reported in original units.  Statistical significance was declared at P < 0.05.

A progress report from the 2015 trail may be accessed at:


We observed no statistical differences across any of the treatments for the variables measured in this trail (Table 1).  However, leaf tissue nutrient concentrations for nitrogen were numerically higher in the OA+BSM treatment and this difference may be biologically relevant (P-value = 0.061).  Tissue nutrient concentrations for phosphorus and potassium were also numerically higher for the OA+BSM treatment, suggesting possible interactive effects between OA and the nitrogen-containing BSM.

It is important to consider that the lack of a response in the mature trial could be due to the fact that plants had a large amount of carbohydrate and nutrient reserves in the tissues from the previous growing seasons.  Plants may also have been recovering from the stress of the 2015 growing season, which was unusually hot and dry.  These carryover effects may mitigate possible treatment effects for the 2016 season.  However, we feel confident that the treatments were successfully applied and washed down into the raspberry plant rhizosphere, as 60 gallons of water were applied per plot immediately after each OA treatment application.

To date, our results show no clear benefit of OA application to mature red raspberry under the conditions of this study.  However, we would like to note that we did observe increase cane and fine root growth in previous trials with immature raspberry.  The aforementioned 2015 progress report provides information on those trials.  These effects may be advantageous in soils of poor quality or with high soilborne disease pressure.


Table 1. Estimated yield, berry weight, soil chemistry, and leaf tissue nutrients of ‘Meeker’ red raspberry treated with organic acid and brassica seed meal amendments, 2016.

Soil chemistry (Spring 2016) Leaf tissue nutrient
Treatmentz Estimated yield (lbs/A) Average berry weight (g) pH P1 K N% P % K %
BSM 11,810 2.7 6.37 50.80 226.97 2.50 0.19 1.43
OA 11,875 2.9 6.47 49.63 283.60 2.96 0.23 1.85
OA+BSM 12,798 2.8 6.47 74.37 244.03 3.25 0.28 2.16
STD 12,913 2.5 6.43 62.47 233.00 2.65 0.21 1.30
P-valuey 0.221 0.699 0.911 0.434 0.592 0.061 0.115 0.127

zTreatment codes: BSM = brassica seed meal, OA = organic acids, OA+BSM = organic acids + brassica seed meal, and STD = standard grower practice (control).

ySignificance at α=0.05; none of the treatments were significant.