2010 Onion Variety Trial

Mike Orzolek, Penn State Horticulture

Onions were grown four rows to a bed with 6 x 6 inch spacing with 48 plants per rep.  They were transplanted out on April 14, 2010 for all but 'Red Candy Apple', 'Sweet Red' and 'EX 16000'.  The 'Red Candy Apple' and 'Sweet Red' bare root transplants were planted on April 28, while the 'EX 16000' bare root transplants were planted on May 10, 2010.  All field grown onion transplants were of variable size and state of desiccation.  The production system is raised beds with black plastic mulch and two rows of drip tape (high flow 0.45 gallons per minute per 100 feet at 12-inch orifice spacing).

A pre-emergence application of Medal at 1.5 pints per acre was applied for weed control.  Fertility was 90 pounds per acre nitrogen, 100 pounds per acre phosphorus, and 100 pounds per acre potassium broadcast and incorporated prior to making raised beds.   Additionally, BioForge was applied at 1.0 pint per acre on April 16, 2010 and through the drip irrigation system, five gallons of Total feed (12-0-1) was applied on April 30 and May 18, 2010.

Onions were harvested July 20 through July 30, 2010 and graded on August 25 and 27, 2010.

I sent ten bulb samples of all onion varieties to Lancaster Agricultural Products, Lancaster, Pennsylvania, on October 21, 2010 for soluble sugar and pyruvic acid analysis.

Results:

Growing conditions early in 2010 were almost ideal for sweet Spanish onions grown on raised beds with plastic mulch and two rows of drip tape compared to the last four growing seasons -- cool and wet.  However, as the season progressed, conditions changed to dry and hot.  Varieties were transplanted in mid-April, about three weeks earlier than normal.  In 2010, onion transplant tops were cut and maintained at a four-inch plant height in the greenhouse prior to transplanting in the field.  Onions were irrigated at least twice a week for three to four hours per application.  Medal herbicide was applied pre-emergence to transplanting onions in the field.  As the onions grew larger, especially in late June, significant grass and a few broadleaf weeds were growing between and in the rows of onions.  The entire field of onions was hand weeded the week of July 1, 2010.

The highest marketable onion bulb yields (over 18.5 tons per acre -- 'Candy' standard) was obtained from the following varieties; 'T-433', 'Ovation', 'Western Giant' and 'New Mexico State University 09-20' ('Candy' is the current sweet Spanish onion standard in Pennsylvania Table 1).  The pungency ratings for the onion varieties in 2010 were lower than those in 2009; all between 1.8 and 4.1 mM of pyruvic acid which correlates to a mild sweet onion flavor (Table 2).  The average pyruvic acid value for all 18 varieties in 2010 was 3.0 and soluble sugars of 6.2 percent.  The highest soluble sugar level was recorded in 'Tequila' at 7.6 percent soluble sugars.  In 2010, 'Medallion' and 'NMSU 09-20' produced the highest percentage of large/jumbo onion bulbs that were 3.0 inches in diameter or larger.  The experimental variety 'EX 16000' from Seminis was planted three weeks later than the other varieties, but on plastic mulch produced 60 percent more bulbs compared to 'EX 16000' on bare ground.