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Evaluation of Systemic Spray Programs to Reduce Onion Center Rot

Horticulture & Turfgrass

Aubrey Shirley
County Extension Agent
University of Georgia
Reidsville

Abstract

The growth of the Vidalia onion industry in Georgia has allowed it to be become a large economic driver in Southeast Georgia, with an estimated farmgate value of $120 million. Onion growers in this region face many disease challenges, both bacterial and fungal. One of the most economically important bacterial diseases is Center Rot (Pantoea spp.) This is the leading cause of loss in Vidalia onions each year. These losses can range from 5 to 10%, and even total losses in severe years in some fields. Given the large economic impact of the Vidalia onion industry in Georgia and the influence of center rot losses, determining effective treatments for this disease is critical for producers. Three years of data were collected by local agriculture agents to evaluate efficacy of four systematic treatment approaches to center rot: low input, growers standard, high input, and organic.   The objective of the study was to determine which approach to center rot control was most effective for growers. Agents planted Vidalia onion varieties ‘Pirate’ or ‘Century’ in 20-ft plots consisting of 4 replications of each treatment with a 3-ft bare-ground buffer between each plot. Natural infection was relied upon for center rot contamination. Each of these treatments were applied with a backpack sprayer calibrated to deliver 33 gal/A at 40 psi through TX-18 hollow cone nozzles. Treatment applications were made based on the input levels during the growing season. Center rot bulb symptoms were assessed 14 days after harvest following incubation at 28° C and 50% relative humidity. Marketable yield, input costs, and total revenue were calculated for each treatment. Based on three year field assessments we observed that integrated management practices had an impact on marketable yield. The ‘high input’ treatment revenue was $1237.00 more per acre than the ‘growers standard’ even with similar infections.  Organic treatment was also $367.00 more per acre than ‘grower standard’ and on average had a 9.04% increase in center rot incidence. Overall, the ‘high input’ treatment led to greater revenue returns.

Authors: Aubrey Shirley, Savannah Tanner, Ross Greene, Jason Edenfield, Derrick Bowen, Steven Powell, Chris Tyson, Lauren Stanley
  1. Aubrey Shirley Tattnall County ANR Agent, UGA Extension, Georgia, 30453
  2. Savannah Tanner Emanuel County ANR Agent, University of Georgia, Georgia, 30401
  3. Ross Greene Evans County ANR Agent, University of Georgia, Georgia, 30417
  4. Jason Edenfield Toombs County ANR Agent, University of Georgia, Georgia, 30436
  5. Derrick Bowen Tattnall County ANR Agent, University of Georgia, Georgia, 30453
  6. Steven Powell Treutlen County ANR Agent, University of Georgia, Georgia, 30602
  7. Chris Tyson Area Onion Agent, University of Georgia, Georgia, 30436
  8. Lauren Stanley Montgomery ANR/4-H Agent, University of Georgia, Georgia, 30445