Evaluating Irrigation Management and ManKocide for Internal Dry Scale and Bacterial Bulb Rots of Onion

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1 Evaluating Irrigation Management and ManKocide for Internal Dry Scale and Bacterial Bulb Rots of Onion Lindsey du Toit and Tim Waters, Washington State University Pacific Northwest Vegetable Association Annual Convention & Trade Show November 2017, Kennewick, WA

2 Onion internal dry scale

3 Milestone, 2015 SV 4643 NT, 2015

4 Fusarium proliferatum Bacterial bulb rot Bacterial bulb rot Yeast rot

5 Bacterial bulb rots common bacteria in soils splash-dispersed favored by heat, moisture, & injured tissue

6 Bacteria isolated from bulbs with internal dry scale in the Columbia Basin 1.Known bulb rot pathogens: a. Burkholderia gladioli b. Pantoea agglomerans c. Enterobacter cloacae 2.Other bacteria (saprophytic, opportunistic, endophytic?) a. Klebsiella b. Gluconobacter c. Serratia d. Acetobacter e. Bacillus

7 Onion growth during heat stress (50 o F) (64 o F) (79 o F) (93 o F) Brewster, J. L Onions and Other Vegetable Alliums, 2 nd Edition. CAB International, Wallingford, UK.

8 Pasco, WA Ontario, OR 2014 Pasco: One of warmest summers on record for Columbia Basin, longest period with max. temp. >90 o F (July 1 to 19), two long periods with max. temp. >100 o F (July 12 to 14, July 28 to 30). Warm fall. Ontario, OR: 45 days >90 o F. Warm nights. Warm fall.

9 2015 Daily maximum temperature in Pasco, WA 22 days >100 o F 113 o F in late June

10 Age of dry scales (leaves) = when heat stress occurred

11 Management of internal dry scale & associated bulb rots Management of irrigation: - during heat stress & at end of season - based on crop demand/use - frequency, amount of water - termination of irrigation at end of season Scout fields for onset of foliar symptoms Submit samples for diagnosis Fungicides & bactericides: - coppers for bacteria, disinfectants (overhead irrigation)? - late season fungicide applications for Aspergillus & Botrytis, but not F. proliferatum (opportunistic) Onion World May/June 2015, pp. 4-7 du Toit, L.J., Waters, T., and Reitz, S Internal dry scale and associated bulb rots of onion. PNW pp.

12 Field Trial Objectives Assess the influence of 3 factors on development of internal dry scale and bacterial bulb rots: Irrigation amount and frequency Copper (ManKocide DF) application Inoculation of plants with 2 bacterial bulb rot pathogens: Burkholderia gladioli and Pantoea agglomerans

13 Materials and Methods 2016 & 2017, WSU Pasco Extension Farm, split-plot RCBD factorial design (2x2x2), 6 reps Planted: Calibra at 142,600 seed/acre on 11 May 2016, and 164,000 seed/acre on 5 April 2017 Drip irrigation until onset of hot weather, then overhead: 30 June - 26 August July - 25 August overhead irrigation treatments: 1. Dry = recommended frequency & amount (4.5 over warm period) 2. Wet = more frequent & greater amount of irrigation (~6.1 )

14 Materials and Methods 2 bactericide treatments: 1. No bactericides appled 2. ManKocide DF (2.25 lb/acre) % surfactant at 40 gpa in morning: 26 August & 6 September 2016, 31 July and 14 August 2017 Overhead irrigation mid- to late afternoon the same days 2 inoculation treatments: 1. Non-inoculated 2. Bacteria inoculated onto plots in the evening = 10 6 cfu/ml of Burkholderia gladioli and Pantoea agglomerans

15 Materials and Methods Bulbs undercut: 14 September 2016, xx September 2017 Bulbs harvested: 5 feet of bed/split plot 4 October September 2017 Yield: # of bulbs and weight of bulbs/size category 50 bulbs rated at harvest, 50 rated after 4 months in storage: Internal dry scale (0 to 3, converted to severity index/plot) Double centers Bacterial, black mold (Aspergillus niger), others

16 2016 Results Bulb yield and size profile Factor (mean) Pre-pack Medium Jumbo Colossal Culls Total Ton/A Ton/A Ton/A Ton/A Ton/A Ton/A Dry 0.4a 7.7a 27.4a 0.8a 0.3a 37.4a Wet 0.3a 5.9b 28.2a 1.0a 0.6a 36.2a Bacteria In. 0.4a 6.6a 26.8a 1.2a 0.7a 36.1a No Bacteria 0.3a 7.0a 28.9a 0.7a 0.2a 37.5a Mankocide 0.2b 6.6a 28.3a 1.2a 0.4a 37.6a No Mankocide 0.4a 7.0a 27.3a 0.7a 0.4a 36.0a LSD p= Significant interaction between inoculation and irrigation treatments: wet plots inoculated with bacteria had more culls than drier, non-inoculated plots.

17 2016 Results: Bulbs at harvest Internal dry scale, bacterial rot, black mold, & double centers Dry scale (0-3 severity index) Bacterial rot (% of bulbs) Black mold (% of bulbs) # Double centers (% of bulbs) Factor Treatment Irrigation Wet 0.95 a 7.2 a 0.00 a 4.7 a Dry 0.99 a 4.2 a 0.70 b 2.8 a LSD Inoculation Inoculated 0.99 a 8.7 a 0.35 a 4.2 a Non-inoculated 0.94 a 2.6 b 0.36 a 3.3 a LSD Bactericide ManKocide 0.96 a 6.0 a 0.10 a 4.2 a No ManKocide 0.98 a 5.4 a 0.61 b 3.4 a LSD # Significant 2-way interaction of irrigation and bactericide treatments

18 2016 Results: After 4 months of storage Internal dry scale, bacterial rot, black mold, & double centers Dry scale (0-3 severity index)* Bacterial rot (% of bulbs)* Black mold (% of bulbs) Double centers (% of bulbs) Factor Treatment Irrigation Wet 0.83 a 8.9 a 0.6 a 5.7 a Dry 0.89 a 5.1 a 2.4 a 6.1 a LSD Inoculation Inoculated 0.87 a 10.7 a 1.7 a 5.9 a Non-inoculated 0.85 a 3.7 b 1.3 a 5.8 a LSD Bactericide ManKocide 0.85 a 7.6 a 1.2 a 5.5 a No ManKocide 0.87 a 6.5 a 1.8 a 6.2 a LSD * Significant 3-way interaction of irrigation, inoculation, & ManKocide treatments

19 Dry scale severity index 2016 Results: Internal dry scale after 4 months of storage

20 Bacterial bulb rot (% of bulbs rated) 2016 Results: % Bacterial bulb rot after 4 months of storage

21 2017 Results Bulb yield and size profile Factor (mean) Pre-pack Medium Jumbo Colossal Culls Total Ton/A Ton/A Ton/A Ton/A Ton/A Ton/A Dry 0.3a 4.7a 36.5a 3.0a 4.1b 44.5a Wet 0.4a 5.2a 33.7b 3.1a 6.1a 42.4a Bacteria Inoc..4a 5.5a 31.9b 2.9a 6.5a 40.7b No Bacteria.3a 4.4b 38.3a 3.2a 3.7b 46.2a ManKocide 0.3a 5.3a 35.0a 3.4a 5.3a 44.1a No ManKocide 0.3a 4.6a 35.2a 2.7a 4.9a 42.8a LSD p= Wet plots had fewer jumbo bulbs & more culled bulbs than plots with optimal irrigation. Inoculated plots had fewer jumbo bulbs and less total yield (more medium + culled bulbs). ManKocide applications did not affect bulb yield (size, culls, or total yield).

22 2017 Results: Bulbs at harvest Internal dry scale, bacterial rot, black mold, & double centers Dry scale (0-3 severity index) Bacterial rot (% of bulbs) Black mold (% of bulbs) Double centers (% of bulbs) Factor Treatment Irrigation Wet 0.68 a 13.9 a 2.3 a 26.5 a Dry 0.63 b 12.4 a 1.3 a 25.3 a LSD Inoculation Inoculated 0.67 a 21.0 a 2.2 a 22.8 b** Non-inoculated 0.63 a 5.3 b 1.4 a 29.0 a LSD Bactericide ManKocide 0.67 a 12.5 a 1.8 a 26.3 a No ManKocide 0.64 a 13.8 a 1.7 a 25.6 a LSD **Difficult to discern doubles on rotten onions

23 Summary Inoculation of plots with P. agglomerans and B. gladioli increased the incidence of bulbs with bacterial rots Excessive irrigation and colonization of onion plants by P. agglomerans and B. gladioli reduced bulb yield significantly in 2017 Plots irrigated excessively had a greater incidence of bulbs with internal dry scale at harvest in 2017 (not in 2016) Surprisingly, excessively irrigated plots did not have significantly more bacterial rot or fewer bulbs with double centers than dry plots in either year Timing of when irrigation treatments were initiated may be too late to influence development of double centers? ManKocide applications had no significant effect on bacterial bulb rots. Increased irrigation frequency and amount of irrigation during the hottest time of the season negatively impacted yield and bulb size in 2017 Storage results from the 2017 trial are pending.

24 Acknowledgements Pacific Northwest Vegetable Association Columbia Basin Onion Research Committee Gina Gray, IRZ Consulting Seed companies OSU: Stuart Reitz, Clint Shock WSU staff: Don Kinion, Jennifer Darner, Erika Ramirez Garcia, Eduardo Sallas, Andrea Vallejo Gutierrez Mike Derie, Brian Henrichs, Barbara Holmes, Erin Miller, Haruka Fukada Play With Your Food