Management of Powdery Mildew in Greenhouse and High Tunnel Tomatoes by Using Ultraviolet C Light

Progress report for ONE20-377

Project Type: Partnership
Funds awarded in 2020: $29,171.00
Projected End Date: 11/30/2023
Grant Recipient: West Virginia University
Region: Northeast
State: West Virginia
Project Leader:
Dr. Mahfuz Rahman
West Virginia University
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Project Information


Production of vegetables such as tomatoes, cucumbers and peppers in protected environments, like greenhouses and high tunnels, has gained popularity in West Virginia due to proven advantages in extending the growing season and potential of intensive use of scarce flat land. However, due to less wind movement and limited escape of plant-transpired water, these structures are prone to high humidity. This leads to the development of destructive diseases, such as powdery mildew and leaf mold, which are less common in open field production system. Due to the limited fungicidal options for managing diseases in protected culture, plant pathologists have developed alternative management options consisted of non-chemical techniques such as lowering humidity and use of ultraviolet radiation that can make disease management sustainable and reduce cost. This project will primarily focus on control of powdery mildew by exposing tomato plants to required amount of UV-C radiation and examine its efficacy on leaf mold in grower cooperators’ greenhouse and high tunnel. Efficacy of UV-C exposure will be determined with 6 rows of tomatoes, where three rows will receive optimized dose of UV-C and another three rows will be left unexposed to demonstrate the efficacy of UV irradiation to field day attendees (preferably high tunnel and greenhouse growers). The grower cooperators have shown strong interest in conducting trials on site.  Additional outreach activities will include local and regional growers’ meetings and newsletter articles.

Project Objectives:

This project seeks to develop a sustainable powdery mildew management method on greenhouse and high tunnel tomato production system by using UV-C light. These UV units can be used repeatedly as and when needed to make it most cost effective, free from environmental pollution and health hazards to workers. This system will make disease management sustainable as the probability of resistance development is very low compared with fungicidal control of powdery mildew. Our objectives are to introduce a new system to the growers and provide them the tips where to get technical cooperation in case they want to get their own UV-C unit assembled and run. This project will capitalize on similar previous work done on multiple crops including tomato, strawberry, cucumber, rose, apple, peach and post-harvest treatment on many different fruits. Specific objectives are:

  1. Assess the usefulness of UV-C light in managing powdery mildew disease in greenhouse and high tunnel;


  1. Optimize the doses, exposure time to attain highest efficacy without any phytotoxicity/avoid damage to plants from light;


  1. Disseminate the technology to organic growers and small farmers through individual communication, grower meetings and conferences, annual field day events, newsletters and cooperative county extension programming.




Powdery mildew is one of the most common diseases of vegetables grown in greenhouses and high tunnels all over the world. Production of vegetables such as tomatoes, cucumbers and peppers in protected environments has gained popularity in West Virginia due to proven advantages in extending the growing season and opportunity of intensive use of scarce flat land in the mountain valley. However, due to less wind movement and limited escape of plant-transpired water, these structures are prone to high humidity. This had led to the development of destructive diseases, such as leaf mold and powdery mildew. In commercially grown tomatoes in the USA, yield losses due to powdery mildew may exceed 50%, depending on the age of the crops when the disease occurs, environmental conditions and effectiveness of fungicides (Grahame and Eric, 2016). Chemical control is often discouraged in protected environments due to the risk of health hazard. Due to the limited fungicidal options for managing diseases in protected environment, plant pathologists have explored alternative management options consisted of multiple non-chemical techniques such as lowering humidity and use of ultraviolet radiation lamps that can make management sustainable. These options can also reduce cost and health hazards, while attaining sustainable disease management. UV is a short wavelength part of electromagnetic radiation, which can be divided further into UV-A, UV-B, UV-C and vacuum UV radiation, with the potential to interrupt the life cycle of fungal pathogens. However, results from multiple studies indicate that UV tolerance of different crops widely vary to avoid phytotoxicity in terms of type of UV and dose (exposure time). For example, UV-B treatments applied on strawberry once or twice weekly during the night for 10 minutes were as effective as the best available fungicides applied on similar schedules for controlling powdery mildew. However, same UV-B dose although controlled powdery mildew on tomato but caused significant phytotoxicity on tomato plants. Thus, UV-C was successfully tested for tomato powdery mildew control. Survey conducted at the high tunnel vegetable production session during WVU small farm conference in 2018 and 2019 revealed that small insects such as spider mites, broad mites, white flies, aphids and a few diseases (leaf mold, powdery mildew) were the major pest issues on high tunnel tomatoes that would need sustainable management options.


Thus, under this project we will utilize a combination of reducing humidity inside the high tunnel and exposing tomato plants to required amount of UV-C to control powdery mildew. Currently there is no data on the efficacy of UV-C on managing leaf mold is available. Although our primary target is powdery mildew, we will collect both PM and leaf mold data in grower cooperators’ greenhouse in the first year and high tunnel in the second year. We have documented severe powdery mildew in grower cooperator’s greenhouse (Appendix 1) and obtained only limited success in controlling it by lowering relative humidity. So, our interest and goal through this project is to demonstrate the efficacy of UV-C exposure to the greenhouse and high tunnel growers.


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Materials and methods:

2021 Progress Report


2020 Progress Report

The success of this project will largely defend on the successful assembly of a low cost UV-C unit capable of autonomous movement in between tomato rows in the high tunnel and greenhouse floor. Due to the pandemic situation, issuance of grant green sheet by WVU-office of sponsored program was delayed until 11/5/2020. We procured all the supplies needed for the assembly of UV-C unit, and made significant progress on its assembly. Tomato plants were grown in the growth chamber and assessing 2-week-old plants in three different groups for phytotoxicity by exposing to UV-C light for different time lengths viz. 10, 15 and 20 seconds followed by 4 hours dark for consecutive two nights. Programming of exposure time was done with a TG-16 mechanical programmable timer plugged into the light source. Preliminary results indicated that exposure time beyond 10 seconds could cause phytotoxicity on tomato plants. However, optimization of exposure time with older plants is now underway.

Methods and Materials as proposed

Implementation of this project will be done in three different phases. In the first phase, we will assemble a UV-C unit suitable to treat tomato plants grown inside the greenhouse and high tunnel. Second phase will be to treat plants in protected culture to optimize the exposure time that provides best suppression of the disease and phase three will be dissemination of the results to other greenhouse and high tunnel tomato growers through a series of outreach activities that will include demonstration of results to potential clientele those who experienced powdery mildew problem in protected cultures, extension educational meetings and publication of newsletter and popular press articles.

Phase I. Principal investigator of the project signed a contract with TRIC Robotics company (Contact: Adam Stager; to obtain a robot from the company on a lease basis for the duration of this project. This Delaware based company currently working in field project in two locations in Delaware and at Kearneysville, WV. This company has active collaboration with Dr. Fumiomi Takeda at Appalachian fruit research station, Kearneysville, WV. Dr. Fumi Takeda agreed to provide free consultation for assembling the UV-C unit. We will use Dr. Takeda’s prototype sketch with minor modification so that abaxial sides of tomato leaves also receive UV-C radiation.  This unit will be a self-propelled UV-C (254 nm) irradiation apparatus with automatic time switches capable of delivering various doses at different times of the night in greenhouse and high tunnel tomato production system culture. Frame will be built by procuring metal and lumber from local store while robot for self-propelling purpose will be leased from TRIC robotics and light bulbs (TUV PL-L 55W) that have a peak emission of 254 nm and irradiation intensity of 0.237 Wm−2 will be bought from Phillips North America Corp., Andover, MA, USA.  Suthaparan et al. (2016) from their study found that radiation ≤ 280 nm strongly reduced conidial germination, hyphal expansion, penetration attempt and infection of Oidium neolycopersici, causal agent of tomato powdery mildew. Lights will be positioned 30 cm from plants at a 30° angle to center light penetration into the upper and lower canopies of the plants.

Phase II. First trial will be set at Mock greenhouse near Berkeley Springs, WV. Mr. Paul Mock has greenhouses that are specifically built for heirloom tomato production. Most of the varieties have very little disease resistance including powdery mildew. These rows are 150’ long. We will select 3 rows that will be subjected to UV-C radiation at night and 3 rows will be left unexposed that will work as non-treated check. Planting distance, trellising and other cultural operations will be done according to grower cooperator’s commercial production system. No chemical or biological products will be applied for disease control. Project personnel will be present on site at the time of first treatment to ensure that the unit moves as programmed and required intervention. Once the exposure time based on actual speed of the unit and movement is optimized, subsequent treatments will be done by grower cooperator. We will provide required training to the grower cooperator to control the unit in case any programming issue arises. The frame will be enclosed with black cloth to prevent any light penetration into the enclosure. To ensure consistent intensity levels, the UV-C light will be turned on at least 10 min prior to irradiation. Irradiance will be measured with a calibrated spectrometer (StellarNet Inc. EPP2000, Tampa, FL) to ensure light intensity doesn’t exceed the level programmed. As previous studies indicated that tomato leaf is more sensitive to UV-C, two exposure levels (15 S and 10 S) will be tested, each on 3 replicate rows with appropriate non-treated check. Treated plants will be evaluated within 72 hours of treatment for potential phytotoxicity. Powdery mildew data will be recorded 5 days after light exposure from both adaxial and abaxial sides of the middle 5 leaves of 10 randomly selected plants of each treated row based on the %leaf area covered with white fungal growth and averaged. A total of 10 consecutive exposure of plants to UV-C followed by collecting data from treated and untreated plants will be done with 10 days interval starting from pre-bloom. The area under the disease progress curve (AUDPC) will be calculated as described by Campbell and Madden (1990) using the following formula:

AUDPC = Σ    [(xi + xi-1)/2][ti - ti-1],

where n is the total number of evaluation times, xi is the proportion of the tomato leaves covered with fungal growth or disease severity (%) at ith observation; t, and (ti – ti–1) is the duration between each assessment. The linear mixed model, MIXED procedure of SAS software (version 9.3, SAS Institute Inc., Cary, NC) will be used to perform the analysis of variance for AUDPC data on powdery mildew severity. Treatment will be considered as fixed effect whereas replicates and exposure time will be considered as random effect. Data will be analyzed for treatment*exposure time for significant interaction effect. Percent data will be checked for homogeneity of variance and normality, transformed as necessary for analysis, and then back-transformed for presentation of results. Treatment means will be compared using Fisher’s protected LSD test at α=0.05. We will also let grower collaborator keep track of yield from the plants that will be used for collecting powdery mildew data. Fruit yield data will be collected by weight and analyzed for significant difference using one-way ANOVA and mean separated by Fisher’s protected LSD test at α=0.05 with SAS software. Data summary will be presented during field day in addition with showing disease severity and fruit quality.

Phase III. In the second year of the project, we will move the UV-C units to the high tunnel of Shafer heritage farm at Bruceton Mills, WV. We reserve the right to explore the possibility of controlling leaf mold in this location. We have documented severe leaf mold occurrence in this location and grower cooperator Joyce Shafer specifically requested to find option for controlling leaf mold in addition with powdery mildew.


Research results and discussion:
Participation Summary
2 Farmers participating in research

Education & Outreach Activities and Participation Summary

5 Consultations
1 On-farm demonstrations
5 Webinars / talks / presentations
1 Workshop field days
1 Other educational activities: WVU extension Ag and Natural Resources research highlights

Participation Summary:

11 Farmers participated
3 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

We plan our major outreach through field days that should accelerate adoption of technology. WV greenhouse and high tunnel growers association strongly supports this project and we will keep the members informed of the results we obtain from the project through our listserve  <>. The major incentive for this work is that the farmers are eager to see this sustainable option work to their expectation. Grower cooperators agreed to disseminate this technology to fellow growers by talking during the field days. Although the target audience for this outreach is small scale organic growers, this practice may be applicable to conventional commercial growers. We anticipate that UV-C will be welcome by most growers as sustainable means of powdery mildew control and crop yield and quality improvement. The main outcome from these on-farm trials will be a long-term science-based sustainable solution for powdery mildew diseases to small farm operators. We will develop web-based publications (bulletins, fact sheets, etc.) on non-chemical means for management of powdery mildew pathogens and share those with farmers through WVU Small farm center and IPM sites. Results will also be presented at WVU certified organic farm field day, during Mid-Atlantic Fruit and Vegetable Convention vegetable session, American Phytopathological Society (APS)-Potomac Division and national meetings.  We plan to provide additional demonstrations on assembling a less expensive relatively small UV-C unit and its operation in a video segment for a future reference to growers with demonstration of UV-C treatments. In addition, we will offer training sessions in concert with other programs such as the WV Small Farm Conference and NE SARE-PDP training opportunities.


Learning Outcomes

2 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:
  1. Germicidal activity of UV-C
  2. Importance of maintaining exposure time to avoid phytotoxicity to tomato plants
  3. Justification behind exposing plants to UV-C at night rather than day time
  4. Justification of reducing relative humidity and use of UV-C simultaneously to achieve better disease control

Project Outcomes

2 Farmers changed or adopted a practice
2 New working collaborations
Project outcomes:

UV-CReport-2022 Low cost UV-C unit was assembled with two rows of UV-C bulbs (10 total) at both sides of the cart (Fig. 1). Due to COVID related restrictions, optimization of  UV-C exposure time that  can effectively suppress powdery mildew (PM) was done in the lab condition. Powdery mildew affected tomato plants were collected from a greenhouse located at Taylor County, WV. These plants were kept in a humid chamber built on the lab bench  where new pot grown tomato plants were brought on a regular basis for PM infection. These plants were used for exposure time optimization(Fig. 2) . Limited greenhouse trials were also conducted for evaluating the efficacy of UV-C on larger plants. Results indicated that UV-C exposure time for suppressing PM varied with plant age. Similarly, UV-C tolerance without any phytotoxic effect also varied with plant age. Cooperating producers were invited to witness the effect and were provided training on the operation of the unit. As the optimization of exposure time for suppression of PM and avoiding phytotoxicity for tomatoes of different growth stages has been completed, cooperators are expected to use the unit in the greenhouse and high tunnels in 2022 and 2023, respectively. 

Assessment of Project Approach and Areas of Further Study:

Powdery mildew is caused by the obligate fungal parasite. This fungal pathogen can't be grown or saved on synthetic media. Naturally infected plants need to be maintained in humid chamber and new plants are needed to be brought in to maintain the inoculum year round for conducting experiment. Utilization of UV-C for tomato disease control is relatively a new technology. Utilization of this tool requires growers understanding and demonstration of results to them. This project is designed to make progress on those gradually. We achieved our initial objectives by assembling a cost-effective UV-C cart. We also optimized  the exposure time that can kill powdery mildew spores without causing any major phytotoxicity. Next step is to let grower cooperators use it in the greenhouse/high tunnel to determine the efficacy of this tool in managing powdery mildew on tomatoes.

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.