Onions (Allium cepa) in southeastern Georgia are almost exclusively transplanted, with the associated high costs and labor requirements. This study was undertaken to evaluate direct-seeded onions as an alternative production method. This study evaluates variety, sowing date, and fertility on direct seeding short-day onions in southeastern Georgia. Sowing dates, early or mid-October (5 and 15 Oct. 2001 and 7 and 21 Oct. 2002), did not affect total, jumbo (≥3 inches diameter), or medium (≥2 inches and <3 inches diameter) yields. Late October sowing (29 Oct. 2001) did not produce sufficient stand or yield to warrant harvesting. Variety also had no affect on yield of direct-seeded onions. Seedstems (flowering), an undesirable characteristic, was significantly greater with the early October sowing date across all varieties compared with the mid- or late- October sowing dates. Neither variety nor sowing date significantly affected plant stand or plant spacing. Fertilization treatments of 150 or 195 lb/acre nitrogen (N) with various application timings and fertilizer sources did not affect total or medium yields. Jumbo yield was affected in only 1 year with calcium nitrate as the primary N source at 195 lb/acre total N having the highest yield, but did not differ from some treatments at 150 lb/acre N. In addition, fertilization treatments did not affect seedstems, plant stand, or plant spacing. Based on this study, we are recommending that growers should direct seed onions in southeastern Georgia in mid-October, plus or minus 1 week depending on field accessibility. In addition, current fertilizer recommendations for transplanted dry bulb onions should be followed, which includes 150 lb/acre N. This eliminates all of the cost and resources required for transplant production.
George E. Boyhan, Juan Carlos Diaz-Perez, Chris Hopkins, Reid L. Torrance, and C. Randy Hill
George E. Boyhan, Albert C. Purvis, William C. Hurst, Reid L. Torrance, and J. Thad Paulk
This study was undertaken to evaluate the effect of harvest date on yield and storage of short-day onions in controlled-atmosphere (CA) storage conditions. In general, harvest yields increased with later harvest dates. Yields of jumbo (>7.6 cm) onions primarily showed a quadratic or cubic response to harvest date, first increasing and then showing diminished or reduced marginal yields. Medium (>5.1 to ≤7.6 cm) onions generally showed diminished yield with later harvests as jumbos increased. Neither days from transplanting to harvest nor calculated degree days were reliable at predicting harvest date for a particular cultivar. Cultivars (early, midseason, and late maturing) performed consistently within their harvest class compared to other cultivars for a specific year, but could not be used to accurately predict a specific number of days to harvest over all years. Only three of the eight statistical assessments of percent marketable onions after CA storage were significant with two showing a linear increase with later harvest date and one showing a cubic trend, first increasing, then decreasing, and finally increasing again based on harvest date.
George E. Boyhan, Reid L. Torrance, and C. Randy Hill
This is a compilation of several studies that were performed to address specific grower concerns or questions about onion fertilization, to assess onion fertility, to make adjustments in soil test recommendations, and to test specific fertilizers for clients covering the 1999–2000 to 2004–2005 seasons. The synthesis of these studies was to evaluate levels of nitrogen (N), phosphorus (P), and potassium (K) fertilizers and their effect on yield, graded yield, and leaf tissue nutrient status in short-day onions over 6 years. In addition, various fertilizers were evaluated for their effect on these parameters. There was a significant increasing quadratic effect on yield from increasing N fertilizer from 0 to 336 kg·ha−1 with an R2 of 0.926. Maximum calculated yield was at 263 kg·ha−1 N fertilizer; however, the yield at this rate did not differ, based on a Fisher's least significant difference (P ≤ 0.05), from our current recommendations of 140 to 168 kg·ha−1 N. Jumbo (7.6 cm or greater) yield performed in a similar fashion. Phosphorus fertilizer rates from 0 to 147 kg·ha−1 had no effect on total yield, but did affect jumbo yields, which decreased linearly with an R2 of 0.322. Evaluations of P fertilizer in the 2001–2002 and 2002–2003 seasons only, when the exact same P fertilizer rates were used, showed a decreasing quadratic effect for jumbo yields with the lowest jumbo yields at 83 kg·ha−1 P fertilizer and jumbo yields increasing with 115 and 147 kg·ha−1 P fertilizer rates. Potassium fertilizer rates from 0 to 177 kg·ha−1 had a quadratic affect on total yield, with the highest yield of 52,361 kg·ha−1 with 84 kg·ha−1 K fertilizer rate. As would be expected, N and P fertilizer rates affected leaf tissue N and P levels, respectively. In addition, N fertilizer rates affected leaf tissue calcium (Ca) and sulfur levels. Potassium fertilizer rates had a significant linear effect on leaf tissue K 3 of 6 years. In addition, K fertilizer rates had a significant effect on leaf tissue P levels. Several fertilizers, including Ca(NO3)2 and NH4NO3, along with complete fertilizers and liquid fertilizers, were used as part of a complete fertilizer program and showed no differences for total yield or jumbo yield 4 of 5 years of evaluation when applied to supply the same amount of N fertilizer. Based on the results of this study, soil test P and K recommendations for onions in Georgia have been cut 25% to 50% across the range of soil test levels.
George E. Boyhan, Albert C. Purvis, William M. Randle, Reid L. Torrance, M. Jefferson Cook IV, Greg Hardison, Ronald H. Blackley, Heath Paradice, C. Randy Hill, and J. Thad Paulk
Short-day onion (Allium cepa) variety trials were conducted in southeastern Georgia from 2000–03. Data collected and evaluated included total yield, graded yield, harvest date, number of seedstems, number of doubles, number of onion centers, bulb shape, disease incidence, bulb pungency, and storability in controlled atmosphere (CA) storage. Fifty-eight varieties were evaluated in the trials with 10 varieties appearing in all 4 years. Twenty-nine varieties appeared only once in the trials. Eight varieties had jumbo yields (≥3-inch diameter) that were not significantly different from the greatest jumbo yielding variety in 2 of the 4 years of testing and included `Century', `EX 19013', `Georgia Boy', `Mr. Buck', `Sapelo Sweet', `Savannah Sweet', `Sweet Vidalia', and `WI-609'. Early season varieties were strongly daylength dependent with foliar lodging occuring early and uniformly. Late season varieties were more prone to bacterial infection particularly if postharvest heat curing was employed. Although significant differences between varieties for seedstems (flower formation) and bulb doubling occurred almost every year, environmental conditions were an important part of their development. Five varieties had seedstems in 2 of the 3 years seedstems were prevalent that did not differ from the greatest number of seedstems for that year and included `Cyclops', `Georgia Boy', `Mr. Buck', `Pegasus', and `SSC 6372 F1'. `Sapelo Sweet' and `Sweet Advantage' had more than 5% bulb doubling in 3 years of the trials. Pungency as measured by pyruvate analysis ranged from 1.1 to 5.4 μmol·g–1 fresh weight (FW) over the 4 years of trials. There were nine varieties that were, for 2 years or more, among the greatest in percent marketable onions after 4.5 months of CA storage: `Georgia Boy', `Granex 1035', `Granex 33', `Ohoopee Sweet', `Sapelo Sweet', `Savannah Sweet', `Sweet Melissa', `Sweet Melody', and `SRO 1000'.
George E. Boyhan and C. Randy Hill
This study evaluated poultry litter, commercial organic fertilizer, and compost for organic production of onion (Allium cepa) transplants within the Vidalia onion growing region of southeastern Georgia. Two field experiments were conducted. The first experiment tested six rates of poultry litter (0–10 tons/acre). The second experiment tested a factorial combination of two rates of nitrogen (N) (0 and 130 lb/acre) and three rates of compost (0, 5, and 10 tons/acre). Seedling weight, length, and diameter were measured ≈10 weeks after sowing. Poultry litter had a significant increasing linear effect on plant weight and diameter. There was also a significant increasing quadratic effect on plant length. Commercial organic fertilizer (3N–0.9P–2.5K) at 130 lb/acre N had a significant effect on plant length, but compost at 0, 5, or 10 tons/acre did not affect plant length. There were organic fertilizer by compost interactions for plant weight and diameter. There was a significant effect on plant diameter with organic fertilizer (130 lb/acre N) and 10 tons/acre compost, but there was no fertilizer effect on plant diameter at 0 or 5 tons/acre compost. The interaction effect on plant weight indicated there was a significant effect from fertilizer with 5 and 10 tons/acre compost, but not with 0 tons/acre. Based on this study, nutrition should not be a problem in producing organic onion transplants in southeastern Georgia. Four to 6 tons/acre fresh poultry litter should be adequate for producing good quality transplants. An alternative approach of using organic fertilizer at a rate of 130 lb/acre N with 5 to 10 tons/acre compost can also be used to produce good quality transplants.
Manish K. Bansal, George E. Boyhan, and Daniel D. MacLean
Vidalia onions (Allium cepa) are a branded product of southeastern Georgia marketed under a federal marketing order. They are short-day, yellow onions with a Granex shape that are susceptible to a number of diseases postharvest, limiting the amount of time they can be marketed. Postharvest treatments and storage methods can help extend their marketability. Thus, the objective of this study was to evaluate these postharvest treatments and storage conditions on quality of three Vidalia onion varieties: ‘WI-129’, ‘Sapelo Sweet’, and ‘Caramelo’. All varieties were undercut, then either harvested immediately (zero cure), field cured (2 days), or forced-air heat cured (3 days at ≈37 °C) when judged mature. ‘WI-129’, ‘Sapelo Sweet’, and ‘Caramelo’ represent early, midseason, and late varieties, respectively. Bulbs were then sorted and stored in refrigerated storage [0–1 °C, 70% relative humidity (RH)], sulfur dioxide (SO2) (1000 mg·L−1 in 2010 and 5000 mg·L−1 in 2011, one time fumigation) followed by refrigeration, ozone (O3 (0.1–10 mg·L−1; continuous exposure, 0–1 °C, 70% RH), or controlled-atmosphere storage [3% oxygen (O2), 5% carbon dioxide (CO2), 0–1 °C, 70% RH]. After 2 and 4 months, bulbs were removed from storage, and evaluated after 1 and 14 days for quality and incidence of disorders. ‘Caramelo’ had the lowest percent marketable onions after curing in 2010, while ‘WI-128’ had the lowest percent marketable onions in 2011. There was a rain event immediately before harvesting ‘Caramelo’ that may have contributed to low marketability in 2010. Heat curing improved marketability for ‘Sapelo Sweet’ and ‘WI-129’ in 2010 compared with no curing. In 2011, heat curing resulted in more marketable onions for ‘Sapelo Sweet’ compared with no curing. Curing had no effect on ‘Caramelo’ in 2011 and field curing had the greatest percent marketable onions for ‘WI-129’ in 2011. In 2010, controlled-atmosphere storage had more marketable onions compared with SO2 for ‘Caramelo’ and was better than simple refrigeration or O3 with ‘WI-129’. In 2011 refrigeration, controlled-atmosphere storage, and O3 were all better than SO2 with ‘Caramelo’. ‘Sapelo Sweet’ and ‘WI-129’, on the other hand in 2011, had better storage with SO2 compared with other storage methods. Onions stored for 2 months had 32% and 17% more marketable onions after removal compared with 4 months of storage regardless of storage conditions for 2010 and 2011, respectively. Poststorage shelf life was reduced by about one-third, 14 days after removal from storage regardless of the storage conditions.
George E. Boyhan, Reid L. Torrance, Jeff Cook, Cliff Riner, and C. Randell Hill
Onions (Allium cepa) produced in southeastern Georgia's Vidalia-growing region are primarily grown from on-farm–produced bareroot transplants, which are usually sown the end of September. These transplants are pulled midwinter (November–January) and are reset to their final spacing. This study was to evaluate transplant size and spacing effects on yield and quality of onions. Large transplants (260–280 g per 20 plants) generally produced the highest yield. Medium transplant size in the range of 130 to 150 g per 20 plants produced satisfactory yield while maintaining low numbers of seedstems (flowering) and doubled bulbs, which are undesirable characteristics. Smaller transplant size (40–60 g per 20 plants) have reduced yields and lower numbers of seedstems and double bulbs. Increasing plant population from 31,680 to 110,880 plants/acre can increase yield. In addition, plant populations of 110,880 plants/acre can increase yields compared with 63,360 plants/acre (industry standard), but only when environmental conditions favor low seedstem numbers. Seedstems can be high because of specific varieties, high plant population, or more importantly, in years with environmental conditions that are conducive to their formation. ‘Sweet Vidalia’ was the only variety that had consistently reduced quality and high numbers of seedstems. ‘Sweet Vidalia’ has a propensity for high seedstem numbers, which may have influenced results with this variety. A complete fertilization program that included 133 or 183 lb/acre nitrogen did not affect onion yield, regardless of variety or population density.
Manish K. Bansal, George E. Boyhan, and Daniel D. MacLean
Vidalia onions (Allium cepa) are very susceptible to infection from pathogens and diseases compared with other types of onions. Botrytis neck rot (BNR) (Botrytis allii) is the most common and destructive storage disease, whereas sour skin (Pseudomonas cepacia) can cause significant bacterial losses, particularly, for late season cultivars. The objective of this study was to assess the effects of different fungicide and bactericide drenches on marketability of Vidalia onions using the cultivar Savannah Sweet grown, harvested, and graded for high-quality onions. Six different fungicide treatments were evaluated, including fludioxonil at two different rates, fluopyram and pyrimethanil in combination, and pyraclostrobin and boscalid in combination with a water-only and an untreated entry. In addition, four different bactericide treatments were evaluated, including copper hydroxide and copper sulfate pentahydrate with a water-only and untreated control. Treatments were applied by drenching the onion bags with 1 gal of solution at the desired concentration. Onions treated with fungicide were inoculated with the pathogen that causes BNR, whereas the bactericide treatments were inoculated with the pathogen that causes sour skin by placing a single inoculated bulb into each bag. Half of the bags were heat-cured for 48 hours and all of the onions were stored immediately under refrigerated conditions at 34 to 36 °F for 2 or 4 months. Bactericide treatments were not heat-cured the second year of the study. Onions were evaluated after 1 and 14 days of shelf life. For both years, all the fungicide applications were effective with more marketable onions compared with the controls. Fludioxonil, fluopyram/pyrimethanil, and boscalid/pyraclostrobin had the highest percentage of marketable onions compared with the water or untreated controls. Fluopyram/pyrimethanil and boscalid/pyraclostrobin fungicides had significantly higher percentage of marketable onions than the controls but were similar to the low rate of fludioxonil. Bactericide applications were not effective in reducing losses when compared with the controls.
George E. Boyhan, Reid L. Torrance, Jeff Cook, Cliff Riner, and C. Randell Hill
Onions (Allium cepa) produced in southeastern Georgia's Vidalia-growing region are primarily grown from on-farm produced bareroot transplants, which are usually sown at the end of September. These transplants are pulled midwinter (November to January) and reset to their final spacing. This study was to evaluate sowing date, transplanting date, and variety effect on yield and quality of onions. Beginning in the first week of November, onions can be transplanted until the end of December with reasonable yield and quality. For example, in the 2003–04 season, total yield of onions transplanted on 22 Dec. 2003 did not differ from any onions transplanted on earlier dates in November or December. In the 2004–05 season, onions transplanted on 20 Dec. 2004, had lower total yield than onions transplanted in November, but were not different from onions transplanted on 4 Jan. 2005. The propensity of some varieties to form double bulbs can be reduced with later sowing and transplanting dates. Sowing the first week of October rather than the fourth week of September and transplanting in December rather than November can reduce double bulbs in some varieties.
Onion production requires N fertilization, yet use efficiency of applied N is low. Improvements may be possible with a better understanding of plant growth and nutrient requirements over time. Onion growth and nutrient uptake was extremely slow during the winter months following planting, then increased substantially in the spring. Onion leaf N concentrations declined with age, while bulb N concentrations fluctuated with growing conditions but showed no longterm trend. Responses to N application were due primarily to timing and less to rate applied. Nitrogen uptake increased in some cases very quickly following N application, and in other situations was still evident after 6½ months. Yield increases, however, occurred only for preplant and winter fertilizer applications, not for spring application. Yield responses to both timing and rate varied by cultivar, with the later maturing cultivar doing best at the highest rate of preplant and the higher 2 rates of the winter applied N fertilizer.