EVALUATION OF THE HOP CYST NEMATODE, HETERODERA HUMULI, AN EMERGING PATHOGEN OF UNITED STATES HOP (HUMULUS LUPULUS) PRODUCTION

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: ACTIVE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1028068
• Grant No.: 2022-68008-36508
• Cumulative Award Amt.: $299,998.00
• Proposal No.: 2021-09846
• Project Start Date: May 1, 2022
• Project End Date: Apr 30, 2026
• Grant Year: 2022
• Program Code: [A1701]- Critical Agricultural Research and Extension: CARE

Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824

Performing Department
ENTOMOLOGY

Non Technical Summary
The Hop Cyst Nematode (HCN), Heterodera humuli, is a threat to United States hop production, which is currently the top producer of hops worldwide. Prior studies have found that the hop cyst nematode causes severe plant stress, nutritional deficiencies, and mechanical injury leaving the plant susceptible to secondary infections. It is also associated with causing yield losses of 38% per string or plant death in some cases (Hafez et al., 1999; Hay & Pethybridge, 2003; Mende & McNamara, 1995). Our recent preliminary findings described within this proposal indicate that the hop cyst nematode is becoming or has become widespread throughout the nation's top-producing regions (Darling et al., 2020; Darling et al. 2021 unpublished) and is posing a risk to yield. Therefore, immediate action should be taken to address this issue. Currently, there are no known effective forms of management for hop growers with hop cyst nematode, so positive samples leave growers with limited options. The key for preventing this aggressive pest of hop production from hindering yield and corresponding economic loss is to determine distribution within key regions, develop effective avoidance/mitigation strategies, and ensure that this information is widely- and easily- accessible to American hop growers

Animal Health Component

80%

Research Effort Categories

Basic

20%

Applied

80%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
212	2230	1120	100%

Knowledge Area
212 - Pathogens and Nematodes Affecting Plants;

Subject Of Investigation
2230 - Hops;

Field Of Science
1120 - Nematology;

Keywords

hop cyst nematode

hops

and nematode management

Goals / Objectives
In this project, our main goals are (1) to help U.S. hop growers find effective strategies to prevent and limit yield losses caused by the HCN; and (2) to collaborate with growers and extension faculty to ensure that developed mitigation and prevention strategies from this proposed research reaches hop growers nationwide

Project Methods
Objective 1. To determine the distribution and severity of impact on U.S. Hop Production1.1 Conduct a survey of hopyards in the Pacific Northwest.1.2 Establish an action threshold for hop cyst nematodes in hopyards.1.3 Determine if any relevant biological differences exist between two U.S. hop cyst nematode populations.Design and Measures: 1.1 Samples will be collected in the fall of years 1 and 2 of this project, a time when population densities of PPN have been demonstrated to be the highest in other PNW crops (East et al. 2021; Zasada et al., 2015). During this time, 25 hop yards will be visited in Oregon, Washington, and Idaho. We will contact collaborators for farm visits tocoordinatecollectingsoil samples Within a field, we will collect soil and roots.1.2 A greenhouse trial will be established to determine the rate at which hops are significantly damaged and therefore would lead to significant yield losses.1.3 We will maintain HCN colonies from WA and MI under greenhouse conditions on hop plants (cv. Centennial).Objective 2. To develop integrated management strategies for hop cyst nematode infested hopyardsDevelop effective hot water dipping procedures to remove hop cyst nematode populations from infested root stock.Determine poor- and non-host cover crops and selected weed species and evaluate if oilseed radish cultivars for trap crop properties.Determine the host status and response of different hop varieties for HCNEvaluate a range of nematicides and soil amendments for their efficacy on controlling hop cyst nematodes.Design and Measures:2.1 We will purchase approximately sixty rhizomes from a clean plant stock source (National Clean Plant Network) and plant each rhizome in 1L polystyrene containers with an 80:20 soil mix (play sand: sterilized field soil) in the MSU Plant Science greenhouses. Five days after plant emergence, we will inoculate pots with 10,000 Heterodera humuli eggs per pot. We will leave eight pots uninoculated to serve as negative controls. Plants will be irrigated and fertilized throughout the trial with a 20:20:20 solution bi-weekly to encourage normal plant growth. Forty-five days later, we will clip and weigh any above ground growth and evaluate each rhizome for HCN infection. Next, we will begin the treatment regime. Five, 20 L containers of water will be heated to 52°C. The treatment plan we propose is detailed in Table 1. Two weeks post treatment, the plants will be visually inspected for phytotoxicity or other symptoms of disease. Bine height measurements will be collected every two weeks until trial conclusion. At trial conclusion, we will record final rhizome weight, above and below ground heights, and visual appearance of the plant and root systems. Then we will select one-inch sections of each rhizome to examine for presence of cysts. Final population densities from soil and root samples will be compared with original inoculum rates to determine if each treatment was effective at reducing hop cyst nematodes.We will repeat the described dips so that each treatment is replicated eight times. Plants will then be re-potted as described above. 2.2a. We will evaluate different cover crops effectiveness in reducing hop cyst nematode. The experiment will be performed in RCBD design with four replications and repeated once. Reproduction of HCN on different species will be the deciding factor which one is a good, poor, or non-host for HCN.2.2b. We will use 6-inch diameter greenhouse pots for this experiment. In each pot, we will plant hop on one side as a control and oilseed radish cultivar on the other side of the same pot.2.3 Field trials on a commercial hopyard in Traverse City, Michigan that is previously identified to be infested with concentrations exceeding 50 cysts/100cc will be used to test currently available nematicides and soil amendments for management of the hop cyst nematode. Two field trials will be established in Years 1 and 2 to test the effect of nematicide treatments and soil amendments. O2.4 The five most widely planted hop varieties will be screened against HCN. Experiments will be conducted by USDA-ARS in Corvallis, OR. Hops will be grown similar to methods described in Objective 2.1. A total of 16 plants/variety will be established with half being inoculated with HCN and the other half non-inoculated. Eight weeks after inoculation plants will be destructively harvested. The tops will be removed and weighted. HCN will be extracted from inoculated pots as described above. The experiment will be conducted at least twice.2.3 In field settings, it is common for plant-parasitic nematodes to be unevenly distributed throughout the field. To prevent any error in nematode collection or product efficacy, plots will be completely randomized within block replications. Each plot will also be individually sampled in a zig-zag pattern and compared to itself throughout the season for reduction or growth in HCN and impact to beneficial nematodes (bacterial, fungal, omnivorous, and predatory nematodes). In between soil sampling each plot, the soil sampler will be sterilized with water and ethanol to remove hitchhiking cysts. To prevent confounding variables, we will monitor and record any presence of disease from fungal pathogens. Samples will be extracted, stored, and recorded as described in 2.2.Objective 3. Extend and enhance the industry's knowledge on PPNs and management strategies.3.1. Conduct pre- and post-implementation surveys of growers nationwide.3.2. Arrange field days and extension outreach days for hop growers.Present results via extension talks and bulletins, peer-edited publications, posters, and any relevant industry meetings every year of the project duration.Design and Measures:3.1 Success of disseminating results and grower implementation of new practices will be measured via grower questionnaires before and after in-person talks and field days. In Year 3, we will also talk to growers about implementing our findings with the Great Lakes Hop Working Group and collaborators in the Pacific Northwest (i.e. Dr. David Gent, YCR) and record the number of growers who implement vs. do not implement our management recommendations.3.2 Hop growers of the Great Lakes Hop Working Group and collaborators in the Pacific Northwest will be invited to participate in field days in Year 2 and 3. Activities will include demos: teaching hop growers how to effectively soil sample around the plant, how to safely sterilize soil probe/equipment, and how to perform rhizome hot water dips.3.3 A variety of extension materials (talks, grower pamphlets, posters, extension publications, videos) will be produced by the team to provide information to both local and national growers. After Year 1 of the field trial, our team will give extension talks at the Great Lakes Hops Working Group meetings and the Great Lakes Fruit and Vegetable Expo meeting in December of each year. For Years 2 and Year 3, pamphlets, extension talks, and posters will be shared with collaborators nationwide. Extension publications will be published on the Michigan State University Extension (MSUE) website. A video featuring our greenhouse and field trials will be distributed among our collaborators. Extension agents like Rob Sirrine and Erin Lizotte from Michigan State University and other collaborating extension agents through the Great Lakes Hop Working and Pacific Northwest will help to reach the growers by distributing these materials nationwide. Furthermore, Yakima Chief Ranches, L.L.C. has committed to aid in reaching its growers in top producing states of Washington, Oregon, and Idaho. Representatives from our team will attend the Society of Nematologists meeting for Year 1, 2, and 3 to share findings among peers. Peer-review journal articles will be published in Year 2 and 3 to share results with the scientific community to culture future work on the hop cyst nematode.?

Progress 05/01/23 to 04/30/24

Outputs
Target Audience:Hops growers, agricultural professionals, fellow scientists, and students Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?We have provided several talks to growers and at scientific meetings How have the results been disseminated to communities of interest?With talks, handouts, and other extension efforts. What do you plan to do during the next reporting period to accomplish the goals? This year in May 2024, we will repeat second year grower field trial at Michigan Hop Alliance to evaluate the effectiveness of organic amendments and nematicides application for the management of hop cyst nematodes. In the greenhouse trial, we will evaluate the effect of different inoculation rates of hop cyst nematodes on hop plant growth. We will evaluate the tolerance level of different hop varieties of Michigan to hop cyst nematodes in a greenhouse trial. In another trial, we will evaluate the host status of different cover crops towards hop cyst nematodes.

Impacts
What was accomplished under these goals? We completed a two-year survey of hopyards of Midwest (Michigan, Ohio, and Minnesota) and counted all samples for presence of plant parasitic and beneficial nematodes. We conducted first year field trial at Michigan hop alliance to assess the efficacy of organic amendments and nematicides application for the management of hop cyst nematodes. We conducted an experiment on efficacy of different composts for suppression of hop cyst nematodes in a greenhouse.

Publications

Progress 05/01/22 to 04/30/23

Outputs
Target Audience:Hops growers, agriculture professionals, fellow scientists, and students Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Usman Muhammed is funded on this grant and will be able to train undergraduates to help with this work. Additionally, senior graduate student Elisabeth Darling has been provided with the opportunity to help train newer graduate student Usman Muhammad because of this grant. The grant also provides professional development by funding travel to conferences, share our work with experts, and gain input from industry and grower stakeholders. How have the results been disseminated to communities of interest?Our work so far was presented at the Great Lake Hop Working Group Annual Meeting: Elisabeth Darling, Usman Muhammad, and Marisol Quintanilla-Tornel. 2023. Plant-feeding nematodes of hops: distribution, management, and the future. Detroit, MI, April 13. Oral presentation. What do you plan to do during the next reporting period to accomplish the goals?This year in May 2023, we have plans to conduct the two field trials at two different hop growers. One conventional trial, where we will evaluate efficacy of different nematicides to reduce the population of hop cyst nematode. In another trial, we will assess the efficacy of different manures/compost against the hop cyst nematode. We will also give a presentation to Society of Nematology Meeting in July 2023, to gain input from other nematology experts and network with other scientific professionals on the importance of hop cyst nematode infestations and distribution. Usman Muhammad, E. Darling, A. Palmisano, L. Núñez-Rodríguez, I.A. Zasada, H. Chung, and M. Quintanilla-Tornel. 2023. Abundance and distribution of plant parasitic nematodes in hop yards in Michigan. Columbus, OH, July 9-14. Poster presentation.

Impacts
What was accomplished under these goals? We conducted a national soil survey that including hopyards of six states (two regions) in Fall 2022. The Pacific Northwest at Oregon State University team surveyed Washington, Oregon, Idaho; the Great Lakes region team at Michigan State University surveyed Michigan, Ohio, and Minnesota. Our teams are currently working together to process and analyze these samples, and results are expected before June 2023. We are giving talks, planning webinars and also preparing news articles in order to extend our research results. Also, we have published articles on our results Here is a talk given to Michigan hop growers Darling, E. and Quintanilla, M. 2022. Plant-eating worms? How soil dwelling nematodes could be limiting your hop yields. Traverse City, MI. January 13. Oral presentation

Publications

• Type: Journal Articles Status: Under Review Year Published: 2022 Citation: N��ez, L.*, Darling, E.*, Chung, H., Zasada, I. and Quintanilla, M. 2022. A Review of the Hop Cyst Nematode, Heterodera humuli. Frontiers in Plant Science. Impact factor: 4.407. In preparation
• Type: Journal Articles Status: Published Year Published: 2022 Citation: Darling, E., Pu, J., Cole, E., Christian, R., Warner, F. W., Zasada, I., Chung, H., & Quintanilla, M. 2020. First report of the Hop Cyst Nematode, Heterodera humuli, in two counties of the Yakima Valley region, WA, USA. Plant Disease, (ja). https://doi.org/10.1094/PDIS-08-20-1769-PDN. Journal impact factor: 3.809