Control of Cucumber Downy Mildew through Nighttime Application of Ultraviolet Light Before and After Infection

Progress report for LNE19-388R

Project Type: Research Only
Funds awarded in 2019: $198,745.00
Projected End Date: 04/30/2022
Grant Recipients: Rensselaer Polytechnic Institute; Mount Sinai
Region: Northeast
State: New York
Project Leader:
Dr. Mark Rea
Lighting Research Center, Rensselaer Polytechnic Institute
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Project Information

Project Objective:

The project goal is to control cucumber downy mildew in the field using nighttime applications of UV-C. The team will conduct a laboratory study to determine optimum pre- and post-infection doses of UV-C. A trailer suitable for cucumber fields housing UV-C lamps in Northeast will be designed and built to demonstrate the efficacy of pre- and post-infection UV-C applications in the field. We will educate Northeast farmers on the practical application of UV-C treatments.


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Question 1: For reducing disease severity from cucumber DM, what dosing regime is the best combination of (a) dose (amount x duration), (b) time of application (pre- or post-inoculation), and (c) interval between dosing (1 per week vs. 2 per week) for nighttime applications of UV-C? (laboratory).

Question 2: Does the efficacy of the best dosing regime increase with UV-reflective material? (laboratory).

Question 3: Is the best dosing regime as effective as conventional fungicide spraying? (field)

Question 4: Is the life-cycle benefit/cost of the UV-C system and dosing regime equal to or less than conventional fungicide spraying equipment and methods?

Materials and methods:

Year 1:

Due to challenges in laboratory experiments of maintaining the cucumber downy mildew inoculum, we decided it was more effective to evaluate multiple conditions in the field. Currently we are working with Jim Ward (of Ward's Berry Farm) and Sue Schuefele to design the experiment. This consists of 10 rows, 300 feet long, that will be divided up randomly into blocks and will test varying doses (from 120 - 580 Joules per meter squared, once per week), as well as with and without a UV reflective mulch. Jim explained the row structure and we discussed the possible mulches that could be used and it appeared that Mylar could be used. We are aiming to complete the experimental field design by February, so that plans for planting, building the dragon and field assessments are in place so we can move forward on those items. 

Year 2:

Attempts to maintain and propagate downy mildew (DM) inoculum in the lab proved to be very challenging in year 1, which made exploring various combinations of UV dose, frequency, and mulch type in the lab difficult. In an effort to explore as many combinations as possible, a field study was designed to capture as many of these factors as possible. A different field layout from that described in the Year 1 narrative above was developed that consisted of twenty one 70 foot long rows. Doses of 120, 240, and 480 J·m-2 were applied both once and twice per week to plants on standard black mulch and reflective mulch. Plots were also included that received no fungicide and conventional fungicide. A document attached contains a field map of the conditions.

Trial Layout - Wards Berry Farm

LRC staff worked with Jim Ward to design a tractor mounted UV applicator that was suited for use on the trial plot. The unit was designed to utilize 6 four-lamp UV fixtures mounted in a semi-circular shape and to be mounted directly to a tractor’s 3 point hitch (category 2). The electrical power to operate the lamps was provided by an on-board gasoline generator. Detailed construction drawings and assembly instructions were developed by the LRC and supplied to Jim and his staff. The construction documents and photos of the completed unit are linked below. The unit was constructed successfully on the farm during the late spring/early summer from materials supplied by the LRC.

Wards Berry Farm - Complete Drawings (3_24_20)

Instructions for assembling UV-C unit

Photos from 2020

Disease ratings were taken weekly by Sue Schuefele from July 27th through September 3rd, when all plants except those in the fungicide treated plots were severely affected by DM. Ratings were made by visually assessing the percentage of leaf area covered in DM lesions (yellowing, necrosis, sporulation) on 10 leaves per plot, then on the percentage of DM within the whole plot. In order to facilitate visual estimations, a walk-through of the whole experimental area was performed first, in order to get a sense for the overall extent of downy mildew severity and any other crop diseases or issues including bacterial wilt or fertility issues. The individual leaf inspections were then conducted using a 10X handlens and inspecting both the upper and lower leaf surfaces, in order to ensure that the researcher was looking carefully at leaf symptoms and not attributing leaf yellowing to DM without evidence of sporulation. Those ten random leaf samples further helped the researcher calibrate their eye and get a more detailed picture of disease severity. Finally, the researcher stepped back and evaluated the whole plot for percent leaf area affected by downy mildew.

The LRC plans to work with Sue Schuefele, Jim Ward, and the members of the advisory committee to develop a field trial design for the 2021 growing season based on the results of the this year’s field trial. Care will be given to ensure the trial design will have appropriate replication to perform statistical analysis on the results.

Research results and discussion:

Year 1:

The below file summarizes the status of experiments, analysis and plans as of December. As described above, we are currently in the process of finalizing plans for spring and summer.

SARE-Cucumber Downy mildew meeting_Q4_12_4_2019

Year 2:

The whole plot data is then used to calculate area under the disease progress curve (AUDPC). AUDPC was calculated from 27 Jul to 3 Sept according to the formula : Σni=1[(Ri+1 + Ri)/2] [ti+1 – ti], where R = disease severity rating (% of leaf surface affected) at the ith observation, ti = time (days) since the previous rating at the ith observation, and n = total number of observations). Values were calculated based on the average percent disease severity across the plot.

Data plots are included in the following document: 2020 Data Figures Only

Due to the lack of replication, no data statistical analysis was completed. The data show that, while some treatments may have had lower disease severity at the earlier timepoints, none of the UV treatments performed as well as the fungicide treated plots on either the black or silver mulch and all were >90% infected, similar to the untreated control, by September 3rd.

Research conclusions:

No updates to report at this time.

Participation Summary
1 Farmer participating in research

Education & Outreach Activities and Participation Summary

Educational activities:

1 Published press articles, newsletters

Participation Summary:

1 Farmers
1 Number of agricultural educator or service providers reached through education and outreach activities
Outreach description:

Year 1:

We have not yet reached this stage of the project, but do have some materials in development from prior projects that we will be able to utilize and build upon. This includes the website that we maintain, which will contain copies of the build plans and educational materials used for in-person presentations: 

Year 2:

In addition to maintaining the materials included on the website, LRC researchers also authored an article featuring the research involving use of UV to combat plant disease. The article specifically mentions this research project and contains a quote from Jim Ward, the cooperating farmer, and was published in January, 2021 in Country Folks Grower magazine. A copy of this article is attached here: Country Folks Grower UV Article - 2021

Learning Outcomes

Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

We are currently in the process of planning field trials. Outreach activities will begin only after we have obtained field trial results. In the meantime, we are actively participating in workshops to educate farmers on use of UV light for squash powdery mildew and strawberry powdery mildew, but these workshops are not under this sponsorship. We have discussed the value of using UV light for cucumber downy mildew mainly with our farmer collaborators to include Jim Ward, Amy Hepworth, Larry Eckhardt, as well as our extension agent collaborator Sue Schuefele and advisory board members Dr. Meg McGrath and Dr. David Gadoury. 

Project Outcomes

2 New working collaborations
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.