The purpose of these experiments was to evaluate the performance of several onion (Allium cepa L.) cultivars in overwinter trials. The Willamette Valley appears to have a suitable climate for production of overwintered onions if bolting, disease, and weed control problems can be overcome. Previous experiments at the North Willamette Station have indicated that late August or early September planting dates are superior to later planting dates for maximum yields. With a June or July harvest, this might allow another crop on the onion ground both before planting and after harvest.
Methods
Plots were seeded on September 3, 1980, and September 15, 1981, in randomized complete block design with three (1980) or four (1981) replications. The plant stands were thinned to no more than 27/m. Plot size was 1 row x 6 m with 0.5 m between rows. The plot area was fertilized with 780 kg/ha (1980-81) or 1,110 kg/ha (1981-82) of 10-20-10 before planting and 4.5 kg/ha of propachlor herbicide was applied immediately after seeding. Additional N was applied as follows: 38 kg N/ha as ammonium nitrate in January 1981 and 112 kg N/ha in April 1981. In 1982, additional N was applied at 56 kg/ha in January, March and April; 4.5 kg/ha of propachlor was applied in November, January, and March of each crop year. Plots were hand-hoed as necessary. All plots were harvested on July 16, 1981, and July 8, 1982. Plant population at harvest was 22-26/m for most cultivars. Several cultivars were selected for storage tests. A sample of bulbs was held at 20°C mean temperature and 70 percent mean relative humidity in mesh bags. Rot and sprouting were evaluated in late October of each year.
Results and Discussion
1980-1981
The 1980-81 winter was exceptionally mild, particularly in January. Most cultivars exhibited significant bolting. Since all cultivars were harvested on the same day, a few were over-mature and suffered some sunscald. However, very little regreening occurred. Some cultivars exhibited a small percentage of split bulb basal plates. This may have been caused by exposure to moisture after tops died down or to onion maggot damage.
In 1981, the highest yielding cultivars in gross weight were Sweet Winter 1909, Red Cross, Keep Well, Senshyu Yellow Globe, OWY 100, and Willamette Sweet (Table 1). Largest mean bulb size was obtained with Sweet Winter 1909, Senshyu Yellow, Red Cross, Keep Well, and OWY 100. When the bulbs which had bolted were subtracted from the total yield, the rankings changed significantly. Highest estimated usable yield was obtained with Red Cross, followed by Keep Well, Dragon Eye, Senshyu Yellow 7991, Sweet Winter 1909, Willamette Sweet, OWY 42, and OWY 100. Imai also yielded very well, but the stand was not thinned and Imai plots were not randomized.
Particularly high quality cultivars in color, lack of bolting and splits, and small neck size included Keep Well, Imai, Senshyu Yellow, and Red Cross (Table 2). Sweet Winter 1909 and Willamette Sweet were also impressive but had a high percentage of bolters. Red Cross was particularly mild-flavored. Cultivars considered overmature at harvest were Amber Express, Red Cross, Express Yellow, and Dragon Eye.
At the end of three-month storage, Keep Well and OWY 100 exhibited the smallest degree of sprouting while 100 percent of the Red Cross bulbs had sprouted (Table 3). Storage rots, molds, and maggot damage were low for all cultivars except Keep Well.
1981-1982
The weather pattern in the 1981-82 winter was normal but no winterkill was observed. The only cultivars exhibiting any bolting were Cima (45%) and Walla Walla Sweet Super Early Strain (1%). The percentage of tops down at harvest ranged from 8 percent for Walla Walla Sweet Early Arbini strain to 95 percent for Top Keeper and Red Cross. However, no cultivar was considered overmature at harvest and there was very little sunscald or regreening.
Highest yielding cultivars were Walla Walla Sweet (Super Early strain), Red Cross, and Top Keeper. Largest bulb size (mean weight of all bulbs) was obtained with the same three varieties. When ranked by yield of No. 1 bulbs (more than 7.5 cm diameter) only, the same three varieties had the highest yield (Table 4). Highest quality cultivars were Walla Walla Sweet Super Early, Top Keeper, Keep Well, Red Cross, OWl 100, and Willamette Sweet (Table 2).
Yields were down somewhat from 1980-81 for cultivars tested both years. The reduction was caused mostly by smaller plant populations but bulb size did decline for a few cultivars.
One hundred bulbs of seven cultivars were placed in storage immediately after harvest. Bulbs were examined at approximately monthly intervals and graded for firmness, rot, and sprouting (Table 5). Willamette Sweet, Top Keeper, and Keep Well had the lowest degree of storage rots and sprouting.
Table 1. Yield and Mean Bulb Weight of Overwinter Onions, 1980-81 Estimated Mean bulb Total yield usable yieldZ Variety wt. (g) Rank (MT/ha) Rank (MT/ha) Rank Sweet Winter 1909 178 1 91.4 1 46X 5 Senshyu Yellow 7985 170 2 96.9 4 38X 10 Senshyu Yellow 7991 164 3 69.3 7 5 4 Red Cross 157 4 80.1 2 72 1 Keep Well 131 5* 77.6 3 66 2 OWY 100 131 5* 74.1 5 44 8 Dragon Eye 123 7 55.6 9 56 3 Willamette Sweet 120 8 69.7 6 45 6* OWY 50 118 9 66.5 8 30X 13 AC 7952 116 10* 44.5 13 36 11* AC 7949 116 10* 39.3Y 14 20X 16* AC 7948 113 12 51.8 10 26X 15 Express Yellow 102 13 39.2 15 39 9 AC 7950 99 14 46.6 11 20X 16* Gladalan Brown 89 15 31.2Y 18 16X 18 Early Golden Globe 88 16 23.4Y 19 12X 19 Amber Express 86 17 36.3 16 36 11* Braeside 79 18 34.4 17 28 14 Pukukohe 76 19 12.8Y 26 3X 22 OWY 42 75 20 44.7 12 45 6* Kitami Ki 69 21 18.6Y 23 0W - Creamgold 67 22 21.8 20 0W - Sapporo Yellow 63 23 19.5Y 22 0W - Sapporo Ki 59 24 20.6Y 21 0W - Creamgold Early 58 25 14.3Y 24 7X 20* Early Locker Brown 48 26 13.5Y 25 7X 20* Imai 109V -- 89.4V --V 80V - LSD (0.05) 39 15.9 ZTotal yield less yield of bolters. YPoor stand, less than 16/meter. X50% or more bolters. W100% bolters. VNot included in replicated planting. Excess stand of ~ 36/m. *Indicates a tie. Table 2. Sources and Quality Characteristics of Overwintered Onions, 1980-81 and 1981-82 Cultivar Bulb Scale Percent Neck Split Diameter Overall or line Source Maturity shape color bolted size bulbs (cm) rating 1980-81 AC 7948 1Z 2Y f-tX 2W 50 MV 1U - 2T AC 7949 1 1 t 2 50 M 2 - 2 AC 7950 1 2 f-t 2 50-60 S 2 - 2 AC 7952 1 3 fg-g 2 20 S 2 - 2 Amber Express 2 1 f-t 1 0 S 3 - 2 Braeside 1 2 g-s 1.5 20 M 1 - 1-2 Creamgold 1 2 dg 1 100 M 1 - 1 Creamgold Early 1 2 g 1 50 M 1 - 1 Dragon Eye 2 1 f-g 2 0 S 2 - 3 Early Golden Globe 1 3 dg 2 50 M 1 - 2 Early Locker Brown 1 2 dg 1 50 M 1 - 1 Express Yellow 1 1 f-t 1.5 5-10 S 1 - 2 Gladalan Brown 1 2 dg 2 50 S 1.5 - 2 Imai 2 2 t 2.5 10 M 1.5 - 3 Keep Well 2 2 t-v 2.5 15 S 1.5 - 3 Kitami Ki 3 2 f-g 1.5 100 L 1 - 1 0WY 42 4 1 f 1 0 S 2.5 - 2 OWY 50 4 3 t-v 1.5 55 M 2 - 3 OWY 100 4 2 fg-t 2 40 M 2 - 3 Pukukohe 3 3 g 2 80 L 1 - 1 Red Cross 2 2 f red,poorS 10 S 1.5 - 3 Sapporo Ki 3 3 s 3 100 L 1 - 1 Sapporo Yellow Globe 3 1 s 3 100 L 1 - 1 Senshyu Yellow 7985 1 3 t 2.5 50 S 2 - 3-4 Senshyu Yellow 7991 1 2 g-t 2 25 M 1.5 - 3-4 Sweet Winter 1909 4 2 ft 2 50 S 1.5 - 4 Willamette Sweet 4 2 fg 1.5 35 S 1.5 - 4 1981-82 Avanti 5 2 fg 1.5 0 S 3 5-7.5 2 Cima 5 3 fg 1.5 45 S 3 5 1 Imai 2 2 f 2 0 S 3 5-7.5 2 Keep Well 2 2 fg 2 0 M 3 7.5 4 OWY 100 4 2 fg 2 0 M 3 7.5 3 Red Cross 2 1 f red,fair 0 M 3 7.5-10 4 Senshyu Yellow 2 2 fg 2 0 M 3 5-7.5 3 Sweet Winter 1909 4 2 fg 1.5 0 M 3 5-10 3 Top Keeper 2 1 fg 3 0 S 3 7.5 4 Walla W. Early Arbini 3 3 g 1 0 L 3 5-7.5 1 Walla W. Super Early 3 2 g 1.5 1 M 3 7.5-10 3-4 Willamette Sweet 4 2 fg 1.5 0 M 3 5-10 3-4 Z1 = International Plant Breeders, Inc., 2 = Takii Seeds, 3 = Onion grower 4 = Dessert Seed Co., 5 = Keystone Seed Co. Yl = early, nearly all tops down at harvest, 2 = mid-season, 3 = late, over 50% tops standing at harvest. Xf = flat; fg = flat globe; g = globe; dg = deep or elongated globe; t = top; s = spindle; tv = top, variable. W1 = poor, light; 3 = dark yellow brown, uniform VS = small, M = medium, L = large. Ul = over 5%, 2 = 1-5%; 3 = less than 1%. T1 = poor, 5 = excellent. Sbleached, sunscald. Table 3. Storage Ratings of Overwinter Onions, 1980-81 Cultivars Percent Sprouted Percent Rotted (10/27/81) Dragon Eye 60 4 (very firm) Keep Well 8 60 (maggot infested) OWY 50 21 4 OWY 100 11 0 Red Cross 100 15 Sweet Winter 1909 45 25 (soft) Willamette Sweet 30 4 Table 4. Yield and Mean Bulb Weight of Overwinter Onions, 1981-82 Yield of all Mean bulb wt. Yield of No. 1Z Cultivar bulbs(MT/ha) Rank all bulbs(g) Rank bulbs(MT/ha) Rank Avanti 38.7 6 131 6 23.2 5 Cima 15.8 12 60 12 0.5 12 Imai 25.2 10 96 10 8.8 11 Keep Well 41.4 5 145 4 23.0 6 OWY 100 38.7 6 125 7 18.9 8 Red Cross 55.4 2 162 2 43.2 2 Senshyu Yellow 31.5 9 108 9 11.7 9 Sweet Winter 1909 36.9 8 140 5 25.0 4 Top Keeper 50.9 3 156 3 38.9 3 Walla W. Early Arbini 24.3 11 84 11 9.0 10 Walla W. Super Early 63.7 1 207 1 54.7 1 Willamette Sweet 42.3 4 115 8 20.3 7 LSD(O.05) 16.2 60 13.6 ZNo. 1 bulbs have minimum diameter of 7.5 cm. Table 5. Storage Ratings of Overwinter Onions, 1981-82 Date Cultivar 8/11 9/20 10/21 Comments (8/11) % soft or rotten Keep Well 0 18 20 Firm OWY 100 17 19 27 ~ getting soft Red Cross 20 29 34 Most firm, some sprouting Sweet Winter 1909 50 68 75 Very soft, some rot Top Keeper 11 14 14 Slightly soft Walla W. Super Early 19 22 48 Soft, some sprouting Willamette Sweet 4 6 7 Slightly soft