Assessment of fungicide product applications and program approaches for control of downy mildew on pickling cucumber in North Carolina

AbstractField studies were conducted in North Carolina to determine the critical period for Palmer amaranth control (CPPAC) in pickling cucumber. In removal treatments (REM), emerged Palmer amaranth were allowed to compete with cucumber for 14, 21, 28, or 35 d after sowing (DAS) in 2014 and 14, 21, 35, or 42 DAS in 2015, and cucumber was kept weed-free for the remainder of the season. In the establishment treatments (EST), cucumber was maintained free of Palmer amaranth by hand removal until 14, 21, 28, or 35 DAS in 2014 and until 14, 21, 35, or 42 DAS in 2015; after this, Palmer amaranth was allowed to establish and compete with the cucumber for the remainder of the season. The beginning and end of the CPPAC, based on 5% loss of marketable yield, was determined by fitting log-logistic and Gompertz equations to the relative yield data representing REM and EST, respectively. Season-long competition by Palmer amaranth reduced pickling cucumber yield by 45% to 98% and 88% to 98% during 2014 and 2015, respectively. When cucumber was planted on April 25, 2015, the CPPAC ranged from 570 to 1,002 heat units (HU), which corresponded to 32 to 49 DAS. However, when cucumber planting was delayed 2 to 4 wk (May 7 and May 21, 2014 and May 4, 2015), the CPPAC lasted from 100 to 918 HU (7 to 44 DAS). This research suggested that planting pickling cucumber as early as possible during the season may help to reduce competition by Palmer amaranth and delay the beginning of the CPPAC.

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Fungicides for Control of Downy Mildew on Pickling Cucumber in Michigan

Plant Health Progress ◽

10.1094/php-04-19-0025-rs ◽

2019 ◽

Vol 20 (3) ◽

pp. 165-169 ◽

Cited By ~ 3

Author(s):

Katelyn E. Goldenhar ◽

Mary K. Hausbeck

Keyword(s):

Downy Mildew ◽

Untreated Control ◽

Field Studies ◽

Pseudoperonospora Cubensis ◽

Relative Area ◽

Disease Progress Curve ◽

Cucurbit Downy Mildew ◽

Disease Progress ◽

Pickling Cucumber ◽

Progress Curve

Michigan growers rely on fungicides to limit cucurbit downy mildew (CDM), incited by Pseudoperonospora cubensis; resistance of the pathogen to fungicides is a concern. We evaluated fungicides against CDM in Michigan field studies from 2015 to 2017. According to the relative area under the disease progress curve (rAUDPC), in 2015, mandipropamid, propamocarb, fluxapyroxad/pyraclostrobin, copper octanoate, and dimethomorph resulted in disease levels similar to the control. These treatments, along with cymoxanil, were similar to the control in 2016. Fungicides that were ineffective during 2015 and 2016 did not limit CDM in 2017. Famoxadone/cymoxanil and fluopicolide did not limit CDM in 2017. Each year, the following treatments were similar for disease based on rAUDPC data: oxathiapiprolin applied alone or premixed with chlorothalonil or mandipropamid, ametoctradin/dimethomorph, fluazinam, mancozeb/zoxamide, cyazofamid, and ethaboxam. An exception occurred in 2017, when ethaboxam was less effective than fluazinam, oxathiapiprolin/chlorothalonil, and oxathiapiprolin/mandipropamid. Mancozeb and chlorothalonil treatments were similar in 2015 and 2017, according to rAUDPC data. In 2017, yields were increased for oxathiapiprolin/chlorothalonil, oxathiapiprolin/mandipropamid, mancozeb, ametoctradin/dimethomorph, mancozeb/zoxamide, ethaboxam, cyazofamid, chlorothalonil, and fluazinam compared with the untreated control.

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Resurgence of Cucurbit Downy Mildew in the United States: A Watershed Event for Research and Extension

Plant Disease ◽

10.1094/pdis-09-14-0990-fe ◽

2015 ◽

Vol 99 (4) ◽

pp. 428-441 ◽

Cited By ~ 46

Author(s):

Gerald J. Holmes ◽

Peter S. Ojiambo ◽

Mary K. Hausbeck ◽

Lina Quesada-Ocampo ◽

Anthony P. Keinath

Keyword(s):

United States ◽

North Carolina ◽

Downy Mildew ◽

The United States ◽

Crop Loss ◽

Eastern United States ◽

Cucumis Sativus L ◽

Cucurbit Downy Mildew ◽

Control Programs ◽

Rapid Spread

In 2004, an outbreak of cucurbit downy mildew (CDM) caused by the oomycete Pseudoperonospora cubensis (Berk. & M. A. Curtis) Rostovzev resulted in an epidemic that stunned the cucumber (Cucumis sativus L.) industry in the eastern United States. The disease affects all major cucurbit crops, including cucumber, muskmelon, squashes, and watermelon. Although the 2004 epidemic began in North Carolina, the cucumber crop from Florida to the northern growing regions in the United States was devastated, resulting in complete crop loss in several areas. Many cucumber fields were abandoned prior to harvest. The rapid spread of the disease coupled with the failure of fungicide control programs surprised growers, crop consultants, and extension specialists. The epidemic raised several fundamental questions about the potential causes for the resurgence of the disease. Some of these questions revolved around whether the epidemic would recur in subsequent years and the possible roles that changes in the host, pathogen, and environment may have played in the epidemic.

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Field Response of Cucurbit Hosts to Pseudoperonospora cubensis in Michigan

Plant Disease ◽

10.1094/pdis-05-14-0500-re ◽

2015 ◽

Vol 99 (5) ◽

pp. 676-682 ◽

Cited By ~ 9

Author(s):

M. C. Cespedes-Sanchez ◽

R. P. Naegele ◽

C. S. Kousik ◽

M. K. Hausbeck

Keyword(s):

Downy Mildew ◽

Cucumis Melo ◽

Disease Onset ◽

Research Field ◽

Pseudoperonospora Cubensis ◽

Plant Introductions ◽

Disease Progress ◽

Pickling Cucumber ◽

Progress Curve ◽

Significant Disease

Downy mildew, caused by Pseudoperonospora cubensis, is a severe foliar disease of many cucurbit crops worldwide. Forty-one cucurbit cultigens (commercial cultivars and plant introductions) from five genera (Cucumis, Citrullus, Cucurbita, Lagenaria, and Luffa) were assessed for susceptibility to P. cubensis in a research field exposed to natural inoculum in Michigan. Eight cultigens from a differential set for pathotype determination were included within the 41 cultigens to detect changes in dominant P. cubensis pathotypes present. No pathotype differences were found between 2010 and 2011. Cucumis melo cultigen MR-1 was less susceptible to Michigan P. cubensis populations than other C. melo cultigens. No symptoms or signs of infection were detected on cultigens of Cucurbita moschata and C. pepo. Disease onset was later in 2011 than 2010; greater than 90% disease severity in pickling cucumber ‘Vlaspik’ was observed in both years. This study confirmed that Cucumis is the most susceptible cucurbit genus, while Citrullus and Cucurbita cultigens were the least susceptible genera to populations of P. cubensis in Michigan. Area under the disease progress curve values indicated that disease progress was limited on all Citrullus cultigens compared with Cucumis cultigens, and pathogen sporulation was not detected under field conditions. Future studies should evaluate the ability of a reduced fungicide program to control downy mildew on less susceptible Cucumis melo ‘Edisto 47’, ‘Primo’, ‘Athena’, ‘Strike’, ‘Ananas’, ‘Banana’, and ‘Tam-Dew’. Many of the melon cultivars evaluated were selected on the basis of reported resistance to downy mildew, yet they showed significant disease symptoms. It is important to evaluate candidate cultigens for resistance to local P. cubensis populations.

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Breeding for Root-knot Nematode Resistance in Cucumber

HortScience ◽

10.21273/hortsci.31.4.623b ◽

1996 ◽

Vol 31 (4) ◽

pp. 623b-623

Author(s):

S. Alan Walters ◽

Todd C. Wehner

Keyword(s):

North Carolina ◽

Yield Loss ◽

Nematode Resistance ◽

Root Knot Nematode ◽

Fruit Number ◽

Pickling Cucumber ◽

Quality Rating ◽

Marketable Fruit ◽

Stage 1 ◽

Trial Performance

Root-knot caused by Meloidogyne spp. is the primary disease of cucumber (Cucumis sativus L.) in North Carolina, causing an annual yield loss of approximately 12 %. All cucumber cultivars we have tested are resistant to M. hapla, but none are resistant to any of the four important nematodes found on cucumber in North Carolina: M. incognita, M. arenaria races 1 and 2, and M. javanica. However, we are preparing to release three cucumber inbreds with resistance to four out of five of those nematodes. `Marion' (NC-44), `Shelby' (NC-45), and `Lucia' (NC-46) are high yielding, monoecious pickling cucumber inbreds that have resistance to M. arenaria races 1 and 2, M. javanica, and M. hapla. Length: diameter ratio was 3.4, 3.0, 3.9 for `Marion', `Shelby', `Lucia' (`Calypso' was 2.9 in the same trial), respectively. Thus, different length requirements for the pickling industry can be met with the three cultivars. Based on the 1995 North Carolina stage 1 pickle trial, performance (as % of `Calypso') for `Marion', `Shelby', and `Lucia' respectively was 79%, 94%, and 115% for total fruit number/ha; 71%, 96%, and 113% for marketable fruit number/ha; and 102%, 84%, and 97% for fruit quality rating. Therefore, nematode resistant cultivars are available that match the performance of the gynoecious hybrid check cultivar for the region.

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First Report of Pseudoperonospora cubensis Causing Downy Mildew on Momordica balsamina and M. charantia in North Carolina

Plant Disease ◽

10.1094/pdis-03-14-0305-pdn ◽

2014 ◽

Vol 98 (9) ◽

pp. 1279-1279 ◽

Cited By ~ 10

Author(s):

E. Wallace ◽

M. Adams ◽

K. Ivors ◽

P. S. Ojiambo ◽

L. M. Quesada-Ocampo

Keyword(s):

United States ◽

North Carolina ◽

Downy Mildew ◽

Leaf Surface ◽

The United States ◽

Pseudoperonospora Cubensis ◽

Post Inoculation ◽

Bitter Melon ◽

First Report ◽

C Cycle

Momordica balsamina (balsam apple) and M. charantia L. (bitter melon/bitter gourd/balsam pear) commonly grow in the wild in Africa and Asia; bitter melon is also cultivated for food and medicinal purposes in Asia (1). In the United States, these cucurbits grow as weeds or ornamentals. Both species are found in southern states and bitter melon is also found in Pennsylvania and Connecticut (3). Cucurbit downy mildew (CDM), caused by the oomycete Pseudoperonospora cubensis, was observed on bitter melon and balsam apple between August and October of 2013 in six North Carolina sentinel plots belonging to the CDM ipmPIPE program (2). Plots were located at research stations in Johnston, Sampson, Lenoir, Henderson, Rowan, and Haywood counties, and contained six different commercial cucurbit species including cucumbers, melons, and squashes in addition to the Momordica spp. Leaves with symptoms typical of CDM were collected from the Momordica spp. and symptoms varied from irregular chlorotic lesions to circular lesions with chlorotic halos on the adaxial leaf surface. Sporulation on the abaxial side of the leaves was observed and a compound microscope revealed sporangiophores (180 to 200 μm height) bearing lemon-shaped, dark sporangia (20 to 35 × 10 to 20 μm diameter) with papilla on one end. Genomic DNA was extracted from lesions and regions of the NADH dehydrogynase subunit 1 (Nad1), NADH dehydrogynase subunit 5 (Nad5), and internal transcribed spacer (ITS) ribosomal RNA genes were amplified and sequenced (4). BLAST analysis revealed 100% identity to P. cubensis Nad1 (HQ636552.1, HQ636551.1), Nad5 (HQ636556.1), and ITS (HQ636491.1) sequences in GenBank. Sequences from a downy mildew isolate from each Momordica spp. were deposited in GenBank as accession nos. KJ496339 through 44. To further confirm host susceptibility, vein junctions on the abaxial leaf surface of five detached leaves of lab-grown balsam apple and bitter melon were either inoculated with a sporangia suspension (10 μl, 104 sporangia/ml) of a P. cubensis isolate from Cucumis sativus (‘Vlaspik' cucumber), or with water as a control. Inoculated leaves were placed in humidity chambers to promote infection and incubated using a 12-h light (21°C) and dark (18°C) cycle. Seven days post inoculation, CDM symptoms and sporulation were observed on inoculated balsam apple and bitter melon leaves. P. cubensis has been reported as a pathogen of both hosts in Iowa (5). To our knowledge, this is the first report of P. cubensis infecting these Momordica spp. in NC in the field. Identifying these Momordica spp. as hosts for P. cubensis is important since these cucurbits may serve as a source of CDM inoculum and potentially an overwintering mechanism for P. cubensis. Further research is needed to establish the role of non-commercial cucurbits in the yearly CDM epidemic, which will aid the efforts of the CDM ipmPIPE to predict disease outbreaks. References: (1) L. K. Bharathi and K. J. John. Momordica Genus in Asia-An Overview. Springer, New Delhi, India, 2013. (2) P. S. Ojiambo et al. Plant Health Prog. doi:10.1094/PHP-2011-0411-01-RV, 2011. (3) PLANTS Database. Natural Resources Conservation Service, USDA. Retrieved from http://plants.usda.gov/ , 7 February 2014. (4) L. M. Quesada-Ocampo et al. Plant Dis. 96:1459, 2012. (5) USDA. Index of Plant Disease in the United States. Agricultural Handbook 165, 1960.

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Downy Mildew Resistance of the Cucumber Germplasm Collection in North Carolina Field Tests

HortScience ◽

10.21273/hortsci.32.3.450b ◽

1997 ◽

Vol 32 (3) ◽

pp. 450B-450

Author(s):

Todd C. Wehner ◽

Nischit V. Shetty

Keyword(s):

North Carolina ◽

Downy Mildew ◽

Germplasm Collection ◽

Field Tests ◽

Plant Introduction ◽

Leaf Damage ◽

Downy Mildew Resistance ◽

Mildew Resistance ◽

Breeding Lines ◽

Production Areas

Downy mildew [Pseudoperonospora cubensis (Berk. & Curt.) Rostov] is an important disease in most cucumber (Cucumis sativus L.) production areas of the world. Resistant cultivars are available, but higher levels are needed if yield losses are to be avoided. The objective of this experiment was to test all available plant introduction accessions, cultivars, and breeding lines (collectively referred to as cultigens) of cucumber for downy mildew resistance under field conditions in North Carolina. Cultigens were tested in 2 years and two replications under natural field epidemics of the disease. Mean ratings for downy mildew leaf damage ranged from 1.3 to 9.0 on a 0 to 9 scale. The most resistant nine cultigens originated from the U.S., and were primarily adapted cultivars or breeding lines. The most-resistant cultigens, for which multiple-year data were available, were Gy 4, `Clinton', PI 234517, `Poinsett 76', Gy 5, `Addis', M 21, M 27, and `Galaxy'. The most-susceptible cultigens for which multiple year data were available, were PI 288995, PI 176952, PI 178886, and PI 211985. We classified 17 cultigens as highly resistant (1.3 to 3.0), 87 as moderately resistant (3.3 to 5.0), 311 as moderately susceptible (5.3 to 7.0), and 248 as highly susceptible (7.3 to 9.0) for the 663 cultigens with multiple-year data. No plant introduction accessions were found to be more resistant than the most-resistant elite cultivars and breeding lines tested.

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First Report of Carboxylic Acid Amide Fungicide Resistance in Plasmopara viticola (Grapevine Downy Mildew) in North America

Plant Health Progress ◽

10.1094/php-01-18-0005-br ◽

2018 ◽

Vol 19 (2) ◽

pp. 139-139 ◽

Cited By ~ 1

Author(s):

Xuewen Feng ◽

Anton Baudoin

Keyword(s):

North Carolina ◽

Carboxylic Acid ◽

North America ◽

Downy Mildew ◽

Acid Amide ◽

Plasmopara Viticola ◽

Carboxylic Acid Amide ◽

Grapevine Downy Mildew ◽

Grape Downy Mildew ◽

Caa Fungicides

This report documents the first known occurrence in North America of resistance in grape downy mildew (Plasmopara viticola) to the carboxylic acid amide (CAA) fungicides mandipropamid and dimethomorph. These fungicides (FRAC group 40) have been an important component of downy mildew management programs for the past decade. Resistant isolates were obtained at three locations in Virginia and one in North Carolina, at considerable distances from each other. Resistance was documented by bioassay and the presence of the G1105S mutation, which has been associated with CAA resistance of P. viticola in other areas. Further survey is needed to determine the geographic extent of this resistance.

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Downy Mildew Resistance of the Cucumber Germplasm Collection in North Carolina Field Tests

Crop Science ◽

10.2135/cropsci1997.0011183x003700040050x ◽

1997 ◽

Vol 37 (4) ◽

pp. 1331-1340 ◽

Cited By ~ 20

Author(s):

Todd C. Wehner ◽

Nischit V. Shetty

Keyword(s):

North Carolina ◽

Downy Mildew ◽

Germplasm Collection ◽

Field Tests ◽

Downy Mildew Resistance ◽

Mildew Resistance

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Cucurbit Downy Mildew ipmPIPE: A Next Generation Web-based Interactive Tool for Disease Management and Extension Outreach

Plant Health Progress ◽

10.1094/php-2011-0411-01-rv ◽

2011 ◽

Vol 12 (1) ◽

pp. 26 ◽

Cited By ~ 18

Author(s):

P. S. Ojiambo ◽

G. J. Holmes ◽

W. Britton ◽

M. Babadoost ◽

S. C. Bost ◽

...

Keyword(s):

North Carolina ◽

Downy Mildew ◽

Monitoring Network ◽

The United States ◽

United States Department ◽

Environmental Implications ◽

North Carolina State University ◽

Cucurbit Downy Mildew ◽

National Monitoring ◽

The Usa

Cucurbit downy mildew (CDM), caused by Pseudoperonospora cubensis, is one of the most important diseases affecting cucurbits worldwide. In the USA, host resistance in cucumber had adequately controlled the disease with very minimal application of fungicides from the late 1960s to 2004. In 2004, there was a resurgence of the disease that devastated the cucumber crop in several states in the eastern USA. Since then, host plant resistance alone has not been sufficient to adequately control the disease and now control relies heavily on application of fungicides. To effectively apply fungicides in a timely manner, cucurbit growers, extension personnel, and crop consultants and advisors can now utilize information on disease occurrence and predicted spread disseminated through the United States Department of Agriculture's CDM ipmPIPE decision support system developed by scientists at North Carolina State University. Based on a survey conducted in Georgia, North Carolina, and Michigan, the CDM ipmPIPE resulted in an average reduction of 2 to 3 fungicide applications in 2009 compared to calendar-based fungicide sprays. With approximately 122,000 acres of cucurbits in these three states, this translates to more than $6 million in savings to the producers in these three states. Economic savings and positive environmental implications of reduced fungicide applications demonstrate the value of a coordinated national monitoring network for management of a plant disease that is disseminated aerially over long distances. Accepted for publication 31 January 2011. Published 11 April 2011.

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