®
Michael D. Rethwisch
Processing onions were treated with AuxiGro in spring 2001. Applications were applied at four and 7.5 weeks prior to harvest. A single application of 4 oz.
product/acre at either four or 7.5 weeks prior to harvest increased yield by approximately 0.7 tons/acre. Two applications resulted in a 1.3 tons/acre yield increase. Differences noted were not statistically different, but the two application treatment provided an increased net return of approximately $95/acre.
Various plant growth regulators have been used in onion production in attempts to increase onion yields, especially where bulb onions are produced, with variable results in the latter half of the 1990s. One product that received a great deal of press during the 1990s for bulb onion production was Triggrr formulation of Triggrr ®
® (Westbridge Corp., Vista, CA) The foliar
(active ingredient is kinetin, a type of cytokinin) reportedly increased bulb onion sizes in several grower trials in Washington (Anon. 1998) and Oregon (Anon. 1996) on varieties such as T-400 (now Frontier) and T-
406, and other various red, yellow and white onions.
Four trials conducted by Oregon State personal in 1998 involving two formulations of Triggrr (Soil Triggrr ®
Triggrr ® ) provided inconsistent results however. Only Foliar Triggrr ® and Foliar
resulted in a statistical significant increase from the untreated check in one of the four trials. These experiments may have had different result had the application of
Foliar Triggrr ® been applied to foliage (as labeled) rather than as a sidedress application, however. Propel TM (active ingredient = 2-hydroxypropanoic acid; Entek Corporation, Elkridge, MD) was also tested in three of the experiments but also provided variable results (Jensen, 1998).
Trials conducted by University of Georgia personnel compared Triggrr and a combination of PGA VII and SuperShot-40 with untreated onions and found no statistical differences at harvest time in two years of trials. Both treatments significantly increased the number of sound onions at 4.5 months of controlled atmosphere storage, however, over the untreated check (Boyhan et al., 2001).
In the late 1990s a new product called AuxiGro ® was introduced. AuxiGro ® is a fairly new product and chemistry for the agricultural industry, with first registration in 1999 by Auxein Corporation (now Emerald BioAgriculture). The active ingredients in AuxiGro ® WP are equal amounts of gamma aminobutyric acid, also referred to as GABA, and Lglutamic acid (each 29.2%). GABA is known to occur in animals, and functions as a neurotransmitter. Some insecticides target the GABA pathway but the mode of action for these insecticides is to block the neurotransmitter
GABA at the neuromuscular junction (16th Crop Protection Reference, 2000). These insecticides either contain the active ingredient abamectin (products such as Agri-Mek ® , Clinch TM and Zephyr ® ) or emamectin benzoate (Proclaim ® ).
Studies involving a combined AuxiGro ® applied in combination with a product like Agri-Mek ® have not been completed to the author's knowledge, but potential for antagonism may exist as the two chemistries appear to be opposing.
This is a part of the 2002 Vegetable Report, University of Arizona College of Agriculture and Life Sciences, index at: http://ag.arizona.edu/pubs/crops/az1292/

In comparison with animals, the role of GABA in plants is not as well documented or understood at this time. Kinnersley
(1997) noted that “mineral analysis of treated plants has shown an increase in the content of macronutrients needed for plant growth with the most consistent increase shown in tissue potassium. In treated rye grass and duckweed, levels of potassium increased more than 200%. The correlation between GABA-mediated increases in plant growth and increases in tissue potassium content led to a working hypothesis that GABA bioactivity is plants is similar to its mechanism of action in animals, where it is known to affect transport of calcium and potassium”. Tindall (2001) notes that plants release GABA through the mitochondria when undergoing a period of stress, with GABA then opening nutrient channels within cell walls, allowing a redistribution of nutrients to areas being affected by outside influences. When AuxiGro ®
(containing GABA) applications are made to onions at bulbing, the GABA redirects nutrients to the growing bulb and carbohydrates can be concentrated in the expanding vegetation.
AuxiGro ® is the only product currently containing GABA chemistry for plant growth registered for usage on onions.
Applications of AuxiGro ® to onions early in the growth cycle apparently result in no apparent response, but those made later in the season have provided consistent and sometimes impressive results. Usage of AuxiGro ® at various rates and timings on bulb onions (sizes 1.25-1.5 inch diameter at application) increased mean tonnage by a minimum average of
29 percent (9 tons/acre) to as much as 42.6% (13.2 tons/acre) in Utah State trials during 1998-1999 (Tindall, 2001).
By early 2001, AuxiGro ® was registered on a diversity of US crops, including fresh market and storage type onions (but not processing/dehydrators), various vegetables, field crops, fruit trees and grapes, and grass seed, although California registrations in 2001 were limited to almonds, grapes (for disease control and to increase soluble solids), onions (fresh market and storage), and processing tomatoes.
This trial was conducted to determine if applications of AuxiGro ® WP to processing onions destined for dehydration grown under low desert conditions (which would also include some expected inherent environmental stress), would provide similar yield responses to those previously noted on bulb onions in other states.
Three treatment regimens of AuxiGro ® WP were designed for this experiment, with one similar to the AuxiGro ® for bulb and storage onions (4 oz AuxiGro ® in each of two applications of AuxiGro ®
label
with second application a minimum of 21 days after the first application and approximately 4 weeks prior to harvest). The treatments compared to untreated dehydrator onions in this experiment were:
A) a single early application of 4 oz/acre of AuxiGro ® approximately 7.5 weeks prior to harvest (April 16)
B) a single late application approximately of 4 oz/acre of AuxiGro ®
(May 14)
at approximately 3 weeks prior to harvest
C) two applications (April 16 + May 14) each consisting of 4 oz/acre of AuxiGro ® (similar to existing label for
bulb onions.
Plots were 1.056 acres in size (12 beds wide on 40 inch centers x field length of 1,150 ft.). Treatments were replicated three times in a randomized complete block design to processing onions (variety = Gilroy Foods 46) destined for dehydration.
AuxiGro ® was applied the first treatment date (April 16) using a SprayCoupe sprayer calibrated to deliver 20 gallons/acre of water with the silicone based surfactant BreakThru (Western Farm Service) added at the rate of 5 oz./100 gallons.
Applications made the second treatment date (May 10) were made by helicopter (H & H Aerial, Blythe, CA) as moist field conditions to ensure proper crop growth did not permit application utilizing ground equipment. May 14 treatments were applied as part of a 20 gallon/acre application which also included BreakThru at the 5 oz/100 gallons rate.
Plots were harvested on June 7-8, 2001 and utilized standard harvesting operations for dehydrator onions (mechanical topping, digging and combining beds, and field pick-up/elevation into trailers for transportation). Onions harvested from the entire plot were placed into a separate trailer set (two trailers - front and back unit) and then weighed at a local scale

(River Valley Farms), with the exception of early + late application plot (eastern replicate). This plot, as it was the last one in the field to be harvested, was placed into three different trailer sets that already had partial loads. Tares and net weights could therefore not be calculated and resulted in yield data being available from only two replicates for this treatment. Net weights and yields per acre were calculated for all other plots. Means of yields form the differing treatments were statistically analyzed using a Fishers least significant difference (StatGraphics P~L~U~S for Windows,
Manuguistics Inc. 1997).
AuxiGro ® treatments resulted in higher mean yields than the untreated check from all treatmentt timings. Yields were very similar if applied 4 or 7.5 weeks prior to harvest (Table 1) with single treatments increasing yields 0.68-0.76
tons/acre (early and late treatment respectively) when compared with the untreated check. Two applications of
AuxiGro ® resulted in the highest yields (1.3 tons/acre more than the check) and are very similar to an accumulative effect of two single applications (0.68 tons early +0.76 tons late =1.44 tons/acre).
Differences in mean yields were not statistically different. Statistically significant differences in yields did exist between replicates, however, but only three replications (and data from only two plots for the early + late treatment) were utilized in the experiment, thereby increasing the difficulty in ascertaining if significant differences in mean yields existed.
All AuxiGro ® treatments resulted in increased mean yields of dehydrator onions in this experiment, with two applications of AuxiGro ® providing the highest yields. Mean yields increased from 3.9-7.5% of the untreated check yields of 17.4
tons/acre, but were much less than those reported on bulb onions. As dehydrator onions are worth approximately
$100/ton, it appears that usage of AuxiGro ® WP will be economical as two 4 oz./acre applications are expected to cost about $35 (Tindall 2001), indicating a positive economic return approximately $95/acre. More testing should be completed to determine if other dehydrator varieties will also respond similarly. Additional applications (more than two) to dehydrator onions may also further increase yields.
Anon. 1996. Grotz' formula for boosting onion packouts. Onion World. 12(5): 6, 11-12, 14-15
Anon. 1998. A growth regulator that really works. Onion World. 14(3): 35-36
Boyhan, G.E., W. M. Randle, A. C. Purvis, P. M. Lewis, R. L. Torrance, D. E. Curry, and D. O. Linton. 2001.
Evaluation of growth stimulants on short-day onions. HortTechnology. 11(1):38-42
Jensen, L. 1998. The effect of two growth regulators on dry-bulb onion production. Oregon State University
Malheur Experiment Station 1998 Annual Report.
http://www.cropinfo.net./AnnualReports/1998/growth.onion.html
Kinnersley, A. M. 1997. The role of gamma aminobutyric acid (GABA) in plant growth and productivity.
(Abstract) National Center for Environmental Research, Office of Research and
Development, United States Environmental Protection Agency, Science to Achieve
Results (STAR) Program. http://es.epa.gov/ncer_abstracts/sbir/other/pp/kinnersl.html
Tindall, T. A. 2001. Utah studies show AuxiGro beneficial. Onion World. 17(5):16-17.
Crop Protection Reference 16th Edition. 2000. Chemical and Pharmaceutical Press, Inc. 2395 pp.

This study was made possible through the cooperation of River Valley Farms, especially Antonio Arguayo. The assistance of Richard Wellman (Certified Crop Care Inc.), was essential to the project. Thanks are also extended to the many personnnel of Gilroy Foods who cooperated and made yield data possible, especially Bob Deneweiler, Mark Dotta and Raul Hernandez.
19
18.5
18
17.5
17
16.5
4 OZ/ACRE ON APRIL
16
4 OZ/ACRE ON MAY
14
4 OZ/ACRE ON APRIL
16 AND MAY 14
TREATMENT AND DATE
UNTREATED CHECK
1
AuxiGro @ 4 oz/acre Early = April 16 (52 days before harvest) 18.08 a + 0.68 tons/acre (+3.9%)
AuxiGro @ 4 oz/acre Late = May 10 (28 days before harvest) 18.16 a
AuxiGro @ 4 oz/acre Early = April 16 (52 days before harvest) 18.71 a
(both at 4 oz) + Late = May 10 (28 days before harvest)
+ 0.76 tons/acre (+4.4%)
+ 1.31 tons/acre (+7.5%)
Untreated check 17.40 a
1 Means in columns followed by the same letter are not significantly different at the p< 0.05 level (Fishers LSD) .