2012 Sweet Spanish Onion Variety Trial

Mike Orzolek, Penn State Plant Science, mdo1@psu.edu

Plot size:  Four row/bed 5.0’ long with 6 x 6 inch spacing – 40 plants/rep.

Transplanting Date: April 13, 2012

Production system: raised bed with black plastic mulch and 2 rows of drip tape – high flow 0.45 gal./min./100 ft at 12” orifice spacing.

Herbicide Application: One post-emergence applications of Chateau at 1.0 oz./A.

Fungicide: None

Fertility:  Broadcast and incorporated 100 lbs./A of N-P-K and an additional 25 lbs./A B applied through the drip tape.  BioForge @ 1.0 pt/A was applied as foliar application to all onion transplants within 24 hours of placing plants in the field.  Five additional applications of Root Feed II @1.0 pt/a plus 5 gal./A of Total Feed 4 (N) were made every week for 5 weeks prior to onion bulbing.
 
Harvest Date: August 9, 2012

Drying:  Bulbs from individual plots were placed in 100 lb. potato Burlap bags and placed on benches in a 30’ x 96’ high tunnel covered with 2 layers of row over for 7 days.

Date Graded: August 26, 2012

Design:  Randomized Complete Block with 3 replications

 Results:
Growing conditions in 2012 were more ideal for sweet Spanish onions grown on raised beds with plastic mulch and two rows of drip tape than the last 4 growing seasons - warm and dry.  Varieties were transplanted in mid-April, about 4 weeks earlier than normal.   In 2012, onion transplant tops were cut and maintained at a 4 inch height in the greenhouse prior to transplanting in the field.  Twenty-five pounds of nitrogen was injected into the drip irrigation tape over a 7-8 week period after transplanting.  Onions were irrigated at least twice a week for 3 to 4 hours per application.  While weed control was good to excellent the first 10 weeks after transplanting, rain in late June resulted in moderate weed populations (both grasses and broadleaves including volunteer buckwheat) between the onion rows.  The single application of Chateau significantly reduced weeds and increased harvesting efficiency.  There was a minor onion thrips population that developed in mid-June.  However the foliar application of Spintor and the injection of Root Power at 2.0 pts./A plus Molybdenum at 0.5 pts./A (Stoller Chemical) into the drip tape on June 16, cleaned up the thrips problem within 2 days and kept the onions thrips free.

The highest marketable onion bulb yield was obtained from the following varieties; Medallion, SON 102, and NMSU 9-20 compared to Candy or Expression (current sweet Spanish onion standards in Pennsylvania Table 1).  The pungency ratings for the onion varieties in 2012 were remarkably low, all below 5.0 mM of pyruvic acid that describes a mild sweet onion flavor (Table 2). Medallion, SON 102, Sarape Café, Latigo and Expression produced the highest percentage of large/jumbo onion bulbs that were 3.0 inches in diameter or larger compared to Candy.  There were 8 red onion varieties in this trial, and both NMSU 9-38 and Red Sky produced very attractive red bulbs with good bulb size, quality and yield.  Both varieties are worth trialing commercially in 2013.  I also evaluated two short day varieties, Pinot Rouge and Chianti, and was surprised at their yields, size and quality.  Transplanting short day onions between March 15 and April 1 coupled with optimum growing conditions would make it possible to grow some short day onions in Pennsylvania, specifically Chianti and Pinot Rouge.

Table 1. The marketable yield of eighteen Spanish onion varieties evaluated at the Horticulture Research Farm, Rock Springs, PA – 2012.

 X – The total marketable yield is based on an onion population of 50,000 plants/A including jumbo and colossal bulb sizes.
Y – The average bulb weight in ounces included all bulbs greater than 2.5 inches in diameter
Z – The percent large bulbs included all onion bulbs greater than 3.0 inches in diameter.

Table 2. The percent harvest, soluble solids and pungency rating of eighteen Spanish onion varieties evaluated at the Horticulture Research Farm, Rock Springs, PA – 2012.

X – Bulbs were evaluated 36 days after post-harvest storage.  The number of sprouted and rotted bulbs per variety was recorded.  Approximately 40 bulbs of each variety were placed in a 40 lb cardboard onion box in 55 F storage.

Y – The percent soluble solids (sugars) as measured by Waters Agricultural Laboratories, Camilla, GA.

Z – Pungency was measured by determining the pyruvic acid content of the bulb by Waters Agricultural Laboratories, Camilla, GA.  Onions may be classified as to pungency according to the following scheme:

*    very mild sweet onion..... 1- 4 mmoles pyruvic acid/kg weight of bulbs

*    mild sweet onion............. 5- 7 mmoles

*    intermediate pungency..... 8-10 mmoles

*    pungent ........................11-15 mmoles

*    very pungent .................... >15 mmoles