The majority of Vidalia onions are produced as a transplanted crop. Seeding in high density plantings in September is followed 8 to 10 weeks later by transplanting to final spacing. This practice is labor intensive and expensive. Direct seeding would save on labor, cost, and time. Traditionally, transplanting has been done because of better winter survival, more uniform stands, and better irrigation management during seedling emergence. Beginning 5 years ago, we began evaluating direct seeding onions. Initially, seedstems (bolting) and lack of uniform stand establishment were the main problems. Sowing in September resulted in almost 100% seedstems and using a belt planter with raw seed resulted in poor singulation for uniform stand establishment. Mid-October ultimately proved to be the best time for sowing Vidalia onion seed. Earlier sowing resulted in more seedstems and later planting did not give the plants sufficient time to grow resulting in later stand loss during cold winter temperatures. Using polymer coated seed and a precision vacuum planter resulted in uniform, even stand establishment. Fertilizer requirements are almost half with direct seeded onions compared to transplanted onions with a reduction in the need for fungicides and herbicides. We have established direct seeded onions both with drip irrigation and overhead irrigation. There was concern that center-pivot irrigation would not be able to sufficiently irrigate fields during seedling establishment with the frequent hot fall days we experience. Since this work was initiated several growers have successfully produced direct seeded onions under center-pivot systems. Direct seeding Vidalia onions requires attention to detail because there is only one opportunity to get it right. Timing is also critical particularly with planting date and herbicide application.
George E. Boyhan, Juan Carlos Diaz-Perez, Reid L. Torrance, Ronald H. Blackley Jr. and C. Randell Hill
Wiley Carroll Johnson III and Jerry W. Davis
adequate spray coverage of targeted weeds ( Boyd and Brennan, 2006 ; Boyd et al., 2006 ; Curran et al., 2004 ; Evans and Bellinder, 2009 ; Johnson and Davis, 2014 ; Shrestha et al., 2012 ; Young, 2004 ). Vidalia ® sweet onion are a dry-bulb onion
W. Carroll Johnson III, David B. Langston Jr., Daniel D. MacLean, F. Hunt Sanders Jr., Reid L. Torrance and Jerry W. Davis
Vidalia ® sweet onion is a dry bulb onion grown in Georgia as a cool-season crop. From 2000 to 2009, Vidalia ® sweet onion plantings ranged from 12,320 to 17,430 acres, with statewide 2009 crop value estimated at $126,108,000 ( Boatright and
George E. Boyhan, Raymond Hicks and C. Randell Hill
There has been interest in producing Vidalia onions organically among both conventional and organic growers. In the 2000–01 season we began to look at producing onions organically. Starting with conventionally produced transplants that were transplanted at standard commercial spacings on beds prepared with 10.2–15.2 cm of incorporated compost and 2,802 kg·ha–1 rate of fresh poultry litter. This was sidedressed with an additional 2,500 less/acre (2,802 kg·ha–1) poultry litter. Yields were about half of conventional onion production. In 2002–03, production of organic transplants with 10.2 cm of incorporated compost with 2.24 t·ha–1 rate of poultry litter, which was followed by an additional sidedressing of 2.24 t·ha–1 rate of poultry litter resulted in similar findings. The weight of harvested transplants was about half that of conventionally produced transplants. In the 2002–03 and 2003–04 seasons various natural mulches were evaluated for weed control. They included wheat straw, oat straw, Bermuda hay, pine straw, and compost. None of these performed better than hand weeding and the wheat straw, oat straw, and Bermuda hay actually reduced yields apparently due to allelopathic effects. Finally in the 2003–04 season rates of poultry litter from 0–22.4 t·ha–1 were evaluated for transplant production with rates of 13.4, 17.9, and 22.4 t·ha–1
yielding plants comparable to conventional transplants. Work continues in the area of organic Vidalia onion production. One of the greatest challenge for future work will be finding a cost-effective and practical method of controlling weeds in transplant production.
W. Carroll Johnson III and Jerry W. Davis
sprayers calibrated for low output; 6 gal/acre ( Brainard et al., 2013 ) and 8 gal/acre ( Ferguson, 2004 ). Vidalia ® sweet onion is a dry-bulb onion grown in Georgia as a cool season crop. In 2011, Vidalia ® sweet onion production accounted for the
Reid Torrance, David Langston and Don Sumner
Metam sodium has been evaluated on onions in Georgia since the mid-1980s for control of various soil pathogens in the production of transplants. Observations also indicated excellent weed control activity. Further work showed significant growth response of transplants, 90% or better weed control, and efficacy of Phoma terrestris, Fusarium, and Pythium. Results were better in comparison studies than found with methyl bromide, chloropicrin, and other fumigation combinations. This led to use of the product in field production of dry bulb onions. Seven years of studies revealed an average yield increase of 190 bushels per acre over the control, even where Phoma terrestris levels were minimal. Today, almost all transplant production includes the use of metam sodium and field use is beginning to be used by growers. With limited crop rotation being practiced in the Vidalia onion belt, metam sodium will continue to play a major role in controlling the ever-increasing levels of Phoma terrestris and maintaining profitability in onion production in Georgia.
George Boyhan, Bill Randle, Anna Resurreccion, Robert Shewfelt, Reid Torrance, Chris Hopkins, Randy Hill and Thad Paulk
Beginning in 2001 the Georgia Department of Agriculture mandated testing of new and existing Vidalia onion varieties under the supervision of the University of Georgia. This was prompted by the introduction of early maturing Japanese overwintering varieties, which were perceived to be more pungent than traditional varieties grown in the Vidalia district. The testing primarily focused on flavor and pungency (pyruvate analysis) to determine suitability as a Vidalia onion variety. Our testing compared varieties to an industry standard, initially variety Granex 33, which was later switched to `Savannah Sweet'. In almost all flavor and pungency tests differences were detected among the varieties, however, since the chosen standard variety usually fell within the middle of the tested range, there was no consistent rejection of a variety. If a different statistical approach had been used it would have been possible to reject several varieties over the course of testing. Using multiple comparison with the best (MCB), a modification of Dunnett's test where the best performing variety for a particular parameter becomes the standard, several varieties would have been excluded, but not all of the early Japanese overwintering types. Finally, in 2005 a consumer acceptance study was conducted with 30 consumers evaluating each of 49 varieties resulted in an LSD (5%) with no differences between the top 38 entries, which included several of the Japanese overwinter types. It is becoming clear that concerns over flavor with these early varieties are unfounded.
George E. Boyhan, Reid L. Torrance, Jeff Cook, Cliff Riner and C. Randell Hill
Georgia's most important vegetable crop is the short-day sweet onion marketed as the Vidalia onion, which had a farm gate value over $125 million in 2005 ( Boatright and McKissick, 2006 ). This high value crop is produced from transplants produced
George E. Boyhan, Reid L. Torrance, Jeff Cook, Cliff Riner and C. Randell Hill
Onion is an important crop in Georgia, with a farm gate value over $125 million in 2005 ( Boatright and McKissick, 2006 ). This important commodity is produced in southeastern Georgia in the Vidalia-growing region, which is protected by Federal
George E. Boyhan, David B. Langston, Albert C. Purvis and C. Randell Hill
Five different statistical methods were used to estimate optimum plot size and three different methods were used to estimate optimum number of replications with short-day onions (Allium cepa L.) for yield, seedstem formation (bolting), purple blotch and/or Stemphylium (PB/S), botrytis leaf blight (BLB), and bulb doubling with a basic plot size unit of 1.5 × 1.8 m (length × width). Methods included Bartlett's test for homogeneity of variance, computed lsd values, maximum curvature of coefficient of variation plotted against plot size, Hatheway's method for a true mean difference, and Cochran and Cox's method for detecting a percent mean difference. Bartlett's chi-square was better at determining optimum plot size with transformed count and percent data compared with yield data in these experiments. Optimum plot size for yield of five basic units (7.5 m length) and four replications is indicated using computed lsd values where the lsd is <5% of the average for that plot size, which was the case in both years of this study. Based on all the methods used for yield, a plot size of four to five basic units and three to five replications is appropriate. For seedstems using computed lsd values, an optimum plot size of four basic units (6 m length) and two replications is indicated. For PB/S two basic units (3 m length) plot size with four replications is indicated by computed lsd values. For BLB a plot size of four basic units (6 m length) and three replications is optimum based on computed lsd values. Optimum plot size and number of replications for estimating bulb doubling was four basic units (6 m length) and two replications with `Southern Belle', a cultivar with a high incidence of doubling using computed lsd values. With `Sweet Vidalia', a cultivar with low incidence of bulb doubling, a plot size of four basic units (6 m length) and five replications is recommended by computed lsd values. Visualizing maximum curvature between coefficient of variation and plot size suggests plot sizes of seven to eight basic units (10.5 to 12 m length) for yield, 10 basic units (15 m length) for seedstems, five basic units (7.5 m length) for PB/S and BLB, five basic units (7.5 m length) for `Southern Belle' doubling, and 10 basic units (15 m length) for `Sweet Vidalia' doubling. A number of plot size-replication combinations were optimum for the parameters tested with Hatheway's and Cochran and Cox's methods. Cochran and Cox's method generally indicated a smaller plot size and number of replications compared to Hatheway's method regardless of the parameter under consideration. Overall, both Hatheway's method and computed lsd values appear to give reasonable results regardless of data (i.e., yield, seedstems, diseases etc.) Finally, it should be noted that the size of the initial basic unit will have a strong influence on the appropriate plot size.