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Summary

Center rot of onion (causal agent: Pantoea ananatis) has emerged as a chronic problem in onion growing regions in the U.S. including Georgia, and it has been responsible for significant economic losses in yield and quality. Presence of multiple sources of inocula (seed, weeds, and insects) and a lack of resistant varieties makes this disease extremely difficult to manage. A collaborative effort between extension specialists and county extension agents was initiated using funding from the Specialty Crop Block Grant to evaluate the impact of weed, thrips and foliar P. ananatis control on the management of center rot. Based on field evaluations, we concluded that effective weed control with herbicide treatments comprised of Dual magnum, Prowl H2O and Goal can reduce center rot severity under field conditions. Further, in a separate field trial we evaluated chemical control for P. ananatis and thrips for the management of center rot. We observed that an effective bactericide program, along with a strong thrips management program, is necessary for effective center rot management. An integrated trial was conducted where “the best performing herbicide, bactericide and thrips programs” were integrated into an IPM program and compared with the grower’s standard. Based on the preliminary economic analysis, the proposed IPM program can result in marketable yield increase of 60 lb increase per acre compared to the grower’s standard practice, which can account for $140 increase per acre. If this IPM program is adopted throughout 10,000 acres (acreage of Vidalia onion in GA), then the projected increase in value of this technology will be $1.4 million.

Situation

Vidalia sweet onion is a specialty vegetable crop, which accounts for 40% of the national spring onion production and has an annual farm-gate value of $150 million (2017). Center rot is the most damaging bacterial disease affecting onions in Georgia, with severe losses occurring both in the field and in storage. Since its first report in Georgia (1997), center rot has been a constant threat to onion producers in GA and other onion producing states. Based on the crop-loss estimates in 2016, center rot epidemic resulted in $3.5 million dollars in losses in GA. The disease is primarily caused by a Gram-negative bacterium, P. ananatis, which is endemic to Georgia as >20 weed species have been reported as possible inoculum reservoirs. Center rot symptoms include necrotic and bleached streaks on young leaves, and in severe cases, it may lead to wilting of plants. The bacterium may also progress to the bulb and predispose bulbs to rot in storage. Under favorable conditions, this disease has potential to cause yield losses up to 100%. The bacterium has the potential to move from foliage to the bulb causing rotting and liquefaction in bulb scales. P. ananatis has the ability to be seed-borne. Presence of multiple sources of inocula (seed, weeds, and insects) and a lack of resistant varieties makes this disease extremely difficult to manage.

Response

A collaborative effort was initiated using funding from the Specialty Crop Block Grant to evaluate the impact of weed, thrips and foliar P. ananatis control on the management of center rot. Based on a field trial in 2020, we concluded that an effective weed control can reduce foliar disease severity of center rot under field conditions. Herbicide treatments that comprised of Goal (oxyfluorfen), Prowl H2O (pendimethalin), and Dual Magnum (S-metochlor) provided significantly better cutleaf-evening primrose control as well as resulted in considerably lower foliar center rot severity compared to other herbicide programs. Another field trial was conducted to optimize a program that comprised of bactericides and insecticide for the management of center rot. We concluded that an effective bactericide program along with a strong thrips management program is necessary for effective center rot management. These field trials were a part of multi-year assessments for finding an optimized integrated program for center rot management. In 2020, an integrated trial was conducted where “the best performing herbicide, bactericide and thrips program” were integrated into an IPM program and compared with the grower’s standard practice. The best performing herbicide program that comprised of Dual magnum, Prowl H2O and Goal along with the best performing bactericide program with Kocide 3000 (applied at bulb-initiation and bulb-swelling stages) and a season-long thrips management program (Radiant, Movento and Torac) were used. Based on foliar disease assessments, disease severity was significantly reduced for the IPM program compared to Grower’s standard program and non-treated check. Bulb incidence of center rot was also significantly lower for the IPM program compared to the grower’s standard program. Marketable yield was also significantly higher for the IPM program compared to the grower’s standard program.

Impact

The results from the field trials (weed control, and thrips and Pantoea sp. control) suggest that an integrated disease management package can be devised for our onion growers that would limit pre- and post-harvest losses. The proposed IPM program resulted from this grant can result in marketable yield increase of 60 lb increase per acre compared to the grower’s standard practice, which can account for $140 increase per acre. If this IPM program is adopted throughout 10,000 acres (acreage of Vidalia onion in GA), then the projected increase in value of this technology will be $1.4 million.

State Issue

Plant Production

Details

  • Year: 2020
  • Geographic Scope: National
  • County: Toombs
  • Location: Vidalia Onion and Vegetable Research Center, Reidsville
  • Program Areas:
    • Agriculture & Natural Resources

Author

  • Dutta, Bhabesh

Collaborator(s)

CAES Collaborator(s)

  • Tyson, Christopher Todd
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Extension Impact