Onion Varieties Graded out of Storage, 1996-1998

Clinton C. Shock, Erik B.G. Feibert, and Lamont D. Saunders
Malheur Experiment Station
Oregon State University
Ontario, OR, 1998

Summary

Commercial varieties and experimental lines of yellow, white, and red onions were compared for yield, grade, and storability. Field observations were made for relative maturity and bolting. Yield and grade were determined out of storage in January. Total yield ranged only from 134 to 526 cwt/acre in 1998. Onion yields were significantly lower in 1998 compared to 1996 and 1997 because of a wetter and cooler than normal spring, a severe hail storm on July 4, and hotter than normal weather in July and August. Significant differences (LSD (0.05)) occurred between varieties in market grades, bolting, maturity, and decomposition in storage.

Introduction

The objectives of this trial were to evaluate varieties of yellow, white, and red onions for bulb yield and quality.

Methods

The 1998 trials were conducted on a Greenleaf silt loam soil with 2.3 percent organic matter and a pH of 6.6. The field had previously been planted to wheat. In the fall, before plowing, 100 lb P₂O₅/acre and 20 lb N/acre were broadcast. The wheat stubble was shredded, and the field was deep-chiseled, disked, irrigated, moldboard-plowed, roller- harrowed, fumigated with Telone C-17 at 20 gal/acre, and bedded.

Beds were knocked down March 30. On March 31 Dacthal at 4 lb ai/acre was applied on an 11-in band along the top of the bed. The Dacthal was incorporated the next day with a bed harrow.

Seed of 58 varieties from 16 companies was planted April 2. Participating seed companies were: American Takii, Aristogene, Asgrow, Bejo, Champion, Crookham, D. Palmer, Dorsing, Harris Moran, Petoseed, Rio Colorado, Rispens Seed, Seedex, Shamrock, Sunseeds, and Vilmorin. Plots were four rows wide and 27 feet long. The experimental design was a randomized complete block with five replicates. The onion seed was planted at 12 seeds per foot of row in single rows on beds spaced 22 in apart using four Almaco cone seeders mounted on a John Deere Model 71 Flexi Planter equipped with disc openers. On April 9, onion rows received 3.7 ounces of 'Lorsban 15G' per 1000 feet of row (0.82 lb ai/acre), and the soil surface was rolled. The soil surface was again rolled with hand rollers on April 14 because of crusting from rainfall. On May 17, alleys 4 feet wide were cut between plots, leaving plots 23 feet long. From May 18 through 22 the seedlings were hand thinned to a plant population of four plants per foot of row (3-in spacing between individual onion plants, or 95,040 plants/acre).

On May 29, 32 lb N/acre as urea was broadcast and incorporated by rain on May 30. One hundred pounds of N/acre as urea were sidedressed on June 4 and July 13. The trial was managed to avoid yield reductions from weeds, pests, and diseases (Table 1). Weeds were controlled with cultivations and low-rate herbicide applications as needed until lay-by. After lay-by the field was hand weeded as necessary. Thrips were controlled with four aerial applications of Warrior and Lannate. Fungal diseases were controlled with four fungicide applications including an application on July 5 following the July 4 hail storm.

Table 1. Pesticides and quantities (ai/acre) applied after onion emergence. Onion variety trial, Malheur Experiment Station, Ontario, OR, 1998.

Date	Fungicides		Herbicides		Insecticides
May 23	Ridomil/Bravo 1.6 lb
June 2	Ridomil MZ Gold 0.58 lb		Goal 1.2 oz, Buctril 3.3 oz, Poast 3.6
June 18			Goal 1.2 oz, Buctril 3.3 oz, Poast 2.9 oz
June 25					Warrior 0.3 oz, Lannate LV 0.49 oz
July 5	Dithane DF 2.3 lb, Kocide 4.5 LF 6.6 oz
July 23					Warrior 0.3 oz, Lannate LV 0.49 oz
July 29					Warrior 0.3 oz, Lannate LV 0.49 oz
Aug. 24	Ridomil MZ Gold 1.5 lb				Warrior 0.3 oz, Lannate LV 0.49 oz

The trial was furrow irrigated as necessary to maintain soil water potential at 8-in depth above -20 kPa. Soil water potential was monitored by eight granular matrix sensors (GMS, Watermark Soil Moisture Sensors Model 200SS, Irrometer Co., Riverside, CA) installed below the onion row at 8-in depth. The last irrigation of the season was on September 5. Bulb maturity ratings for each plot were recorded on August 26, September 3, and September 17, as visual estimates of the percentage of dry leaf material in each plot, and percentage of bulbs with necks collapsed and leaves on the ground. Those percentages for each date were averaged for maturity ratings. Bolted onions were estimated as the number of bulbs in the 4-row plot on September 17.

The onion bulbs were lifted on September 17 to field-dry. Onions from the middle two rows of every plot were topped by hand on September 28 and placed into storage in wooden crates on September 29. In early October, the storage shed was heated long enough to achieve an internal onion bulb temperature at 1 cm depth of 90 ⁰F, to reduce storage rot. The storage shed was managed to maintain an air temperature of approximately 34 ⁰F.

Onions were graded out of storage January 5 -7, 1999. Bulbs were separated according to quality: bulbs without blemishes (No. 1s), split bulbs (No. 2s), neck rot (bulbs infected with the fungus Botrytis allii in the neck or side), plate rot (bulbs infected with the fungus Fusarium oxysporum), black mold (bulbs infected with the fungus Aspergillus niger), and bulbs with translucent rings. The No. 1 bulbs were graded according to diameter: small (< 2¼ in), medium (2¼ to 3 in), jumbo (3 to 4 in), and colossal (4 in and larger). Varietal differences were compared using ANOVA and least significant differences at the 5 percent probability level, LSD (0.05).

Results and Discussion

Crops suffered from suboptimal growing conditions in 1998. The growing season started out cooler and wetter than normal. The month of May had 4.55 in of precipitation compared to the 50-year mean of 1.02 in. May had 29 percent fewer and June had 18 percent fewer growing degree days (50 -86 ⁰F) than the previous 10-year mean. A severe hail storm on July 4 resulted in close to 100 percent onion leaf loss. Plants were reduced to 2-in high, injured stubs. The months of July and August were hotter than normal. Weather station data recorded 11 days with maximum air temperatures of 100 ⁰F or higher compared to the 50-year mean of 5 days. There were far more degree days in the above optimal range (86 -104 ⁰F) in 1998 compared to the previous 8-year mean; 70 percent more in July and 29 percent more in August. The hot weather in July and August was suboptimal for onions especially for the regrowth of hail-damaged onions where most of the soil surface was unprotected from solar heating. Average onion yields at the Malheur Experiment Station were substantially lower in 1998 compared to 1996 and 1997 (Figure 1).

Varieties are listed by company in alphabetical order and ranked by bulb yield for each company's varieties for 1996, 1997, and 1998 (Tables 2, 3, and 4). The LSD (0.05) values at the bottom of each table should be considered when comparisons are made between varieties for yield and grade. Differences equal to or greater than the LSD (0.05) value for a column should exist before any variety is considered different from any other variety in the category compared in that column.

Total yield out of storage averaged only 306 cwt/acre in 1998 with a wide range of yield and grade (Table 4). Total yield out of storage ranged from 134 to 526 cwt/acre and colossal size onion yield ranged from 0 to 42 cwt/acre, depending on variety. Significant varietal differences were recorded in all size classes.

Decomposition in storage averaged 3 percent of total yield (Table 4). Neck rot averaged 2 percent, plate rot averaged 0.6 percent, and black mold averaged 0.4 percent. Losses to plate rot could have been greater than the numbers recorded because onions with this defect usually lose most of their weight before being graded out of storage. Bulbs with translucent rings averaged 1.3 percent. The number of bulbs with translucent rings could have been higher since only suspected bulbs were cut during grading. Split bulbs averaged 11.6 percent. Varietal differences in bulb quality in terms of percent of total yield were only significant for plate rot, translucent rings, and split bulbs (No. 2s). Bolting averaged 0.5 bolted onions out of approximately 368 onions in each 4-row plot. The variety with most bolting had only 4 per plot, or just over one percent.