Washington Tree Fruit Research Commission

Research Reports

Fungicide evaluation for the control of bull’s eye rot of apple (2016)

FINAL PROJECT REPORT
WTFRC Project #
YEAR 0/0
Organization Project #
Title:Fungicide evaluation for the control of bull’s eye rot of apple
PI:Mark Mazzola
Organization:USDA-ARS Tree Fruit Research Laboratory
 PDF version of report

Co-PIs

Chang Lin Xiao

USDA-ARS

559-596-2722

chang-lin.xiao@ars.usda.gov

9611 S Riverbend Ave.

Parlier, CA 93648

 

Christian Aguilar

WSU-TFREC

509-664-2280 ext. 243

1104 N Western Ave

Wenatchee, WA 98801

 

Objectives

(1) Evaluate the efficacy of select pre-harvest fungicides and post-harvest fungicide drenches for the control of bull’s-eye rot of apple incited by Neofabraea perennans and Cryptosporiopsis kienholzii.

(2) Determine the effectiveness of fungicide applications in the control of early versus late season apple fruit infection by N. perennans and C. kienholzii occurring in the field.

Significant findings

During both annual trials of this experiment, the only pre-harvest fungicide treatment providing statistically significant pre-harvest control of bull’s eye rot caused by Neofabraea perennans or Cryptosporiopsis kieholzii was thiophanate-methyl (Topsin-M).

During both annual trials of this experiment, the only postharvest fungicide treatments providing statistically significant control of bull’s eye rot caused by N. perennans or C. kienholzii were thiabendazole (Mertect) and pyrimethanil (Penbotec).

Inoculations conducted later in the growing season (at two weeks before harvest) resulted in higher incidences of bull’s eye rot compared to early and mid-season inoculation periods (eighteen and five weeks before harvest, respectively). Regardless of inoculation timing, the pre-harvest fungicide thiophanate-methyl, and postharvest fungicides thiabendazole and pyrimethanil were most effective for control of N. perennans and C. kienholzii infections.

RESULTS

Efficacy of pre-harvest fungicide applications

      Only two fungal inoculation time-points were explored during the first year of this study, (five and two weeks prior to harvest). Infection was significantly greater when inoculations were conducted at two weeks prior to harvest compared to inoculations at five weeks before harvest (P < 0.0001). Overall the proportion of apples with bull’s eye rot decay due to N. perennans infection was not significantly different from infections attributed to C. kienholzii (P=0.0960). Average bull’s eye rot recovery for fruit treated with zinc (Ziram), and pyraclostrobin plus boscalid (Pristine) was not significantly different from average disease incidence recorded in the no fungicide control treatment. Only fruit treated with thiophanate-methyl (Topsin-M) exhibited a statistically significant lower disease incidence (P<0.0001; Table 1). 

      An additional inoculation time-point meant to simulate early season fruit infection was conducted during the second year of this experiment, (eighteen weeks before harvest). A significantly greater proportion of fruit were infected when inoculations were conducted at two weeks before harvest compared to five and eighteen weeks before harvest (P<0.0001). A statistically greater incidence of infection attributed to N. perennans was observed compared to inoculations with C. kienholzii (P=0.0193). Similar to the previous year, the only pre-harvest fungicide that effectively reduced N. perennans and C. kienholzii infections was thiophanate-methyl (P<0.0001; Table 1).

Efficacy of postharvest fungicide drenches

             Inoculations conducted during the first year of this study yielded a greater incidence of bull’s eye rot when N. perennans and C. kienholzii were applied at two weeks prior to harvest rather than five weeks (P<0.0001). In general, greater incidence of disease was attained when fruit inoculations were conducted using a spore suspension of N. perennans instead of C. kienholzii (P=0.0002). Bull’s eye rot recovery for fruit treated with fludioxonil (Scholar) was not statistically different from recovery rates observed for the no fungicide control. Applications of thiabendazole (Mertect) and pyrimethanil (Penbotec) to N. perennans and C. kienholzii inoculated fruit prior to storage resulted in significantly less bull’s eye rot (P<0.0001), with thiabendazole treated fruit exhibiting less disease on average compared to fruit treated with pyrimethanil (Table 2). 

            During the second year of this study, bull’s eye rot incidence was significantly higher when pathogen inoculum was applied to fruit two weeks prior to harvest rather than five and eighteen weeks before harvest (P<0.0001). Inoculations using a spore suspension of N. perennans conidia yielded significantly more bull’s eye decayed fruit compared to C. kienholzii inoculations (P<0.0001). Bull’s eye rot incidence for fruit treated with fludioxonil prior to storage was proportionally as high as fruit left untreated. Application of difenoconazole plus fludioxonil (Academy) to pathogen inoculated fruit only slightly reduced bull’s eye rot incidence compared to the no fungicide control. Only fruit treated with thiabendazole or pyrimethanil demonstrated a significant reduction in bull’s eye rot due to N. perennans and C. kienholzii inoculations (P<0.0001; Table 2).

 

DISCUSSION

In light of the temporary suspension of shipment of Washington grown apples to the Chinese market and subsequent strict phytosanitary regulations established in response to postharvest decay pathogens (Warner, 2014), bull’s eye rot has become an economically important disease for pome fruit growers and packers of the Pacific Northwest region. Once considered a minor disease in Washington State, bull’s eye rot outbreaks have become increasingly more common over the past decade. In effort to curtail the occurrence of bull’s eye rot in this area, various fungicides registered for use on pome fruit were selected and their efficacy against bull’s eye rot was tested. Results from this study indicate that among the pre-harvest and postharvest fungicides evaluated, only thiophanate-methyl (Topsin-M), pyrimethanil (Penbotec) and thiabendazole (Mertect) were effective in providing adequate control of bull’s eye rot in stored apple relative to a no treatment control. While results from this study obviously provide growers and packers with invaluable information pertaining to bull’s eye management, it also highlights the complexities encountered by members of the apple industry in dealing with postharvest decay issues.

As benzimidazole fungicides, thiophanate-methyl and thiabendazole are classified as having moderate to high risk of resistance developing in pathogen populations (Fungicide Resistance Action Committee). This fact has already been demonstrated by the appearance of thiabendazole-resistant strains of Penicillium expansum (Li and Xiao, 2008) and Botrytis cinerea (Zhao et al., 2010) throughout cold storage facilities in Washington State. The short life cycle and high sporulation capacity of P. expansum make it a likely candidate for developing resistance to high risk fungicides. Neofabraea species, however, are comparatively slow growing, and in requiring water splash for spore dissemination, are less capable of spreading at a high rate thus posing less of a risk for developing fungicide resistance. Nevertheless, thiophanate-methyl-resistant strains of N. perennans and N. alba have already appeared in pathogen populations originating from Northern Germany, partially in response to excessive use of this fungicide (Weber and Palm, 2010). The fact that two of the most effective fungicides available to pome fruit growers for bull’s eye rot control share a common mode of action, should be of concern for the Washington apple industry. In order to minimize the potential for resistance, chemistries with differing modes of action should be alternated regularly. As a fungicide belonging to the anilinopyrimidine class, pyrimethanil seemingly presents a useful alternate fungicide as part of a bull’s eye rot management program. Unfortunately, pyrimethanil resistance has also appeared in P. expansum populations originating in Washington State (Xiao et al., 2011), further confounding bull’s eye rot management. While the primary aim of this project was to provide growers with information concerning fungicides that can be used to successfully manage bull’s eye rot, the results from this work further highlight the resounding need for additional fungicides registered for use in pome fruit production systems.

REFERENCES

Fungicide Resistance Action Committee. FRAC code list 1: Fungicides sorted by FRAC code. http://www.frac.info/.

Li, H.X. and Xiao, C.L. 2008. Characterization of fludioxonil-resistant and pyrimethanil-resistant phenotypes of Penicillium expansum from apple. Phytopath. 98(4): 427-35.

Warner, G. “Washington apple producers hope to resume exports to China.” Good Fruit Grower 15 August 2014 Web. 11 March 2015.

Weber, R.W.S. and Palm, G. 2010. Resistance of storage rot fungi Neofabraea perennans, N. alba, Glomerella acutata and Neonectria galligena against thiophanate-methyl in Northern German apple production. Journal of Plant Disease and Protection 117(4): 185-191.

Zhao, H., Kim, Y. K., Huang, L., and Xiao, C. L.  2010.  Resistance to thiabendazole and baseline sensitivity to fludioxonil and pyrimethanil in Botrytis cinerea populations from apple and pear in Washington State.  Postharvest Biology and Technology 56:12-18.

Table 1. Average recovery of bull’s eye rot from cv. Fuji apples inoculated with spores of either Neofabraea perennans or Crytosporiopsis kienholzii at various pre-harvest periods and treated with select pre-harvest applied fungicides.

Year

Pathogen

Inoculation period (weeks before harvest)

Pre-harvest fungicide

Average bull’s eye rot recovered (%)

2014

Neofabraea perennans

5 wbh

No fungicide control

63.75%

Zinc (Ziram)

62.50%

Pyraclostrobin + boscalid (Pristine)

58.75%

Thiophanate-methyl (Topsin-M)

15.00%

2 wbh

No fungicide control

78.75%

Zinc (Ziram)

81.25%

Pyraclostrobin + boscalid (Pristine)

81.25%

Thiophanate-methyl (Topsin-M)

27.50%

Cryptosporiopsis kienholzii

5 wbh

No fungicide control

49.25%

Zinc (Ziram)

37.50%

Pyraclostrobin + boscalid (Pristine)

60.00%

Thiophanate-methyl (Topsin-M)

7.50%

2 wbh

No fungicide control

88.75%

Zinc (Ziram)

65.00%

Pyraclostrobin + boscalid (Pristine)

90.00%

Thiophanate-methyl (Topsin-M)

17.50%

Table 1 (continued). Average recovery of bull’s eye rot from cv. Fuji apples inoculated with spores of either Neofabraea perennans or Crytosporiopsis kienholzii at various pre-harvest periods and treated with select pre-harvest applied fungicides.

Year

Pathogen

Inoculation period (weeks before harvest)

Pre-harvest fungicide

Average bull’s eye rot recovered (%)

2015

Neofabraea perennans

18 wbh

No fungicide control

17.50%

Zinc (Ziram)

22.50%

Pyraclostrobin + boscalid (Pristine)

23.75%

Thiophanate-methyl (Topsin-M)

8.75%

5 wbh

No fungicide control

31.25%

Zinc (Ziram)

22.50%

Pyraclostrobin + boscalid (Pristine)

32.50%

Thiophanate-methyl (Topsin-M)

14.00%

2 wbh

No fungicide control

69.75%

Zinc (Ziram)

38.75%

Pyraclostrobin + boscalid (Pristine)

57.50%

Thiophanate-methyl (Topsin-M)

16.25%

Cryptosporiopsis kienholzii

18 wbh

No fungicide control

36.25%

Zinc (Ziram)

10.00%

Pyraclostrobin + boscalid (Pristine)

21.25%

Thiophanate-methyl (Topsin-M)

12.50%

5 wbh

No fungicide control

12.50%

Zinc (Ziram)

17.50%

Pyraclostrobin + boscalid (Pristine)

17.50%

Thiophanate-methyl (Topsin-M)

11.00%

2 wbh

No fungicide control

52.50%

Zinc (Ziram)

37.50%

Pyraclostrobin + boscalid (Pristine)

43.75%

Thiophanate-methyl (Topsin-M)

10.00%


Table 2. Average recovery of bull’s eye rot from cv. Fuji apples inoculated with spores of either N. perennans or C. kienholzii in the field at various pre-harvest periods and treated with select postharvest applied fungicides.

Year

Pathogen

Inoculation period (weeks before harvest)

Postharvest fungicide

Average bull’s eye rot recovered (%)

2014

Neofabraea perennans

5 wbh

No fungicide control

61.25%

Fludioxonil (Scholar)

52.50%

Pyrimethanil (Penbotec)

17.50%

Thiabendazole (Mertect)

8.75%

2 wbh

No fungicide control

60.00%

Fludioxonil (Scholar)

73.75%

Pyrimethanil (Penbotec)

61.25%

Thiabendazole (Mertect)

20.00%

Cryptosporiopsis kienholzii

5 wbh

No fungicide control

51.25%

Fludioxonil (Scholar)

62.50%

Pyrimethanil (Penbotec)

2.50%

Thiabendazole (Mertect)

1.25%

2 wbh

No fungicide control

89.00%

Fludioxonil (Scholar)

86.25%

Pyrimethanil (Penbotec)

1.25%

Thiabendazole (Mertect)

2.50%

Table 2 (continued). Average recovery of bull’s eye rot from cv. Fuji apples inoculated with spores of either N. perennans or C. kienholzii in the field at various pre-harvest periods and treated with select postharvest applied fungicides.

Year

Pathogen

Inoculation period (weeks before harvest)

Postharvest fungicide

Average bull’s eye rot recovered (%)

2015

Neofabraea perennans

18 wbh

No fungicide control

17.50%

Fludioxonil (Scholar)

27.50%

Pyrimethanil (Penbotec)

6.25%

Thiabendazole (Mertect)

10.00%

Difenoconazole + Fludioxonil (Academy)

20.00%

5 wbh

No fungicide control

48.75%

Fludioxonil (Scholar)

36.25%

Pyrimethanil (Penbotec)

17.50%

Thiabendazole (Mertect)

12.50%

Difenoconazole + Fludioxonil (Academy)

25.00%

2 wbh

No fungicide control

68.75%

Fludioxonil (Scholar)

41.25%

Pyrimethanil (Penbotec)

14.00%

Thiabendazole (Mertect)

28.00%

Difenoconazole + Fludioxonil (Academy)

52.50%

Cryptosporiopsis kienholzii

18 wbh

No fungicide control

26.25%

Fludioxonil (Scholar)

26.25%

Pyrimethanil (Penbotec)

1.25%

Thiabendazole (Mertect)

5.00%

Difenoconazole + Fludioxonil (Academy)

18.25%

5 wbh

No fungicide control

21.25%

Fludioxonil (Scholar)

15.00%

Pyrimethanil (Penbotec)

1.00%

Thiabendazole (Mertect)

0.00%

Difenoconazole + Fludioxonil (Academy)

10.00%

2 wbh

No fungicide control

60.00%

Fludioxonil (Scholar)

52.50%

Pyrimethanil (Penbotec)

1.00%

Thiabendazole (Mertect)

6.00%

Difenoconazole + Fludioxonil (Academy)

37.50%

EXECUTIVE SUMMARY

The primary objectives of this research were to evaluate the efficacy of various pre-harvest and postharvest applied fungicides for control of bull’s eye rot caused by Neofabraea perennans and Cryptosporiopsis kienholzii. To accomplish this goal, fungicide evaluations were conducted in the orchard at multiple pathogen inoculation intervals and the trials were replicated across two years. Data from both years consistently indicated that among the fungicides tested, thiophanate-methyl is the only pre-harvest fungicide capable of adequate bull’s eye rot control while pyrimethanil and thiabendazole were the only two postharvest chemistries providing acceptable control of these two pathogens.

These data come at a pivotal time as bull’s eye rot and other postharvest diseases native to the Pacific Northwest now present quarantine concerns for international trade. During the year prior to China’s temporary trade closure of Washington grown apples, the value of Washington apples shipped to China was estimated at $6.5 million. Interception of Sphaeropsis rot, speck rot and bull’s eye rot on apples exported from Washington resulted in a two year shut down that potentially cost the Washington apple industry $13 million. The need to identify fungicides that can effectively manage bull’s eye rot is high, and while this research accomplishes this need, it also emphasizes the need for additional research in this area.

The three fungicides identified as effective against bull’s eye rot only provide temporary relief for this complex situation. Issues regarding fungicide resistance are a major concern that can only exacerbate the future of bull’s eye rot management. Newly registered fungicides for use in pome fruit production have become available during the course of this study. These new fungicides provide a great opportunity for additional work to be completed in this research area.

Currently, in vitro spore germination and mycelial growth assays using fungicide amended media are being conducted in the Mazzola laboratory for control of bull’s eye rot and other fungi causing economically important postharvest disease. The outcome of this work appears promising, and should contribute much needed information to strengthen bull’s eye management.

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