Application of Ultraviolet Light and MilStop to Restrict Powdery Mildew Infestation in Vegetable Greenhouses

Progress report for ONE22-413

Project Type: Partnership
Funds awarded in 2022: $28,131.00
Projected End Date: 03/31/2024
Grant Recipient: Rodale Institute
Region: Northeast
State: Pennsylvania
Project Leader:
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Project Information

Summary:

Rodale Institute's researchers and growers at Pocono Organics are handling this study to illustrate the effect of UV-light and MilStop (80% potassium bicarbonate fungicide labeled for the use in organic production) on powdery mildew in organic greenhouses. A crop yield loss of up to 60% caused by powdery mildew can be observed in greenhouses with severe infestation. The proposed integrated method for controlling microbial diseases can be introduced as an alternative for chemical applications in conventional and organic agroecosystems. This research project has been conducting in a Pocono Organic's certified Organic vegetable greenhouse located in Long Pond, PA [USDA plant hardiness zone 5b] since September 2022. To conduct this project a UV-light chamber was built and placed in a dark room (shed) in a greenhouse. The UV-light chamber was equipped by UV-C and UV-B lamps. The light intensity was measured with the use a UV-C meter at different distances from the source of light to estimate the amount of energy received by the exposed plants.  A preliminary test was also conducted in a small scale to educate the researchers involved in this project to work with the UV-light. In late-December 2022, 1,500 lettuce seeds were planted in seedling trays to run the first replication of this trial. Bed preparation was also conducted in a certified regenerative organic greenhouse to transplant the seedlings in mid-January. The process of data collection will be started in late January 2023 and the whole project will be replicated three times before summer 2023. To conduct the outreach objective, Rodale Institute researchers will talk about application of UV-light to control agricultural pest and diseases at the Tri-State Greenhouse IPM workshop on January 26 at the University of Vermont. The result of research will be also presented in the Rodale Institute's annual specialty crop workshop in late March 2023. Since establishing a powdery mildew culture is required to conduct this project, a plant pathologist was invited to join the team of researchers and will help PI/Co-PIs to rear powdery mildew under a laboratory condition.

Project Objectives:

This research project seeks to develop an integrated pest management technique to control powdery mildew in organic lettuce production.

 The specific objectives are:

  1. Determine percent reduction in powdery mildew severity on greenhouse lettuce when exposed to UV-lights and MilStop fungicide compared to non-treated control.
  2. Assess the fractional green canopy cover (%FGCC), yield and nutrient quality of greenhouse-grown lettuce treated with UV-light and MilStop.
  3. Establish a demonstration greenhouse with the aim of educating vegetable growers and researchers in the field of crop production and pest management.

The potential results obtained from this research will help growers to adapt new approaches to control microbial diseases in their vegetable greenhouses. The proof of this proposed IPM method may become a feasible and strong methodology to replace application of chemical pesticides with the aim of improve sustainability in the Northeast agroecosystems.

Introduction:

Powdery mildew is a destructive fungal disease in greenhouses that affects several species of vegetable crops. This disease appears as small white to gray powdery spots on the vegetable seedlings’ foliage and can easily spread to the entire greenhouse after transplanting. There are several fungal species that can cause powdery mildew (Omer et al., 2005). The damage intensity in greenhouses depends on fungus species, crop species, and management methods. In 2015, a total cost of $239 million was estimated for powdery mildew management in California. A crop yield loss of up to 60% caused by powdery mildew can be observed in greenhouses with severe infestation. Lettuce (Lactuca sativa L.) is an important leafy vegetable owing to its fast growing and commercial value. It is often used in salads, soups, and wraps. Powdery mildew significantly influences the yield and quality of lettuces and is often considered as a secondary disease. The epidemics of lettuce powdery mildew have been observed in 2013 and 2014 in northeaster US greenhouses. The disease is favored by low light, warm conditions (60°F to 80°F) and cool nights. Overcrowding conditions of plants is also favorable for disease development.

Bicarbonate salts are well known for their antimicrobial characteristics. Potassium bicarbonate is used to suppress infestations of a wide range of microbial diseases. Research results from a greenhouse study at the University of Florida illustrated that potassium bicarbonate formulated as MilStop was significantly more effective than other types of tested bio-fungicides on powdery mildew suppression. Although application of high concentrated potassium bicarbonate solution reduces the fruit and vegetable quality (Fallir et al., 1997), an adjusted concentration of this biocompatible fungicide can restrict disease developments in plants.

Utilization of UV-light can reduce the quality of plant tissues for herbivore pests and interfere with insects’ navigation and behaviors. Using non-ionizing Ultraviolet light to control fungal diseases has been considered as an alternative method for conventional pest management approaches. UV-light was used for disinfection of microbial contaminants by preventing their growth. UV radiation is classified into three categories: UV-C (λ = 100-279 nm), UV-B (λ = 280-314 nm), and UV-A (λ = 315-399 nm). UV-C has the greatest germicidal impact while UV-B induces expression of gene involved in microbial and insect-pest resistance in some plants. High energetic UV-C can penetrate cell membrane and causes chemical damage and mutations in organisms. Since most of the UV-C radiations are absorbed by the stratospheric ozone molecules, there is no other natural source of UV-C on earth.

Exposure of plants to UV-light delays spores’ germination and causes an increased resistance to plant pathogens by promoting the concentration of antimicrobial substances, such as, terpenoids. It was observed that exposure to UV light can reduce the powdery mildew impacts up to 41% in strawberry greenhouses. Research has shown that UV-B radiation increased radish root mass and contents of chlorophyll, carotenoids, and total proteins (Nithia et al., 2005), whereas it reduced carrot fresh mass and total biomass in lettuce (Paul et al., 2012). Literature is scant on the effect of UV radiation on vitamins and synthesis of secondary metabolites in vegetables. Scientists observed that ascorbic acid (vitamin C) concentration was increased when linden leaves were exposed to UV-B for a short period of time, but it was decreased with a long-term UV-B exposure in soybean (Majer and Hideg, 2012b; Ambasht and Agrawal, 2003).

Exploring new pest management techniques with lower environmental impacts is crucially needed for profitable and sustainable organic farming. In this partnership research project, we will evaluate an integrated management approach to reduce powdery mildew severity by using two suppression techniques including 1) seedling exposure to UV-lights and 2) application of a biocompatible fungicide. In this study, we will expose infested lettuce seedlings to UV-lights to control powdery mildew before transplanting. This will be combined with the application of MilStop (80% potassium bicarbonate fungicide labeled for the use in organic production) to reduce powdery mildew infestation in vegetable greenhouses. Although this proposed approach is designed to combat powdery mildew as the main disease, it can also have an impact on other major pathogens in greenhouses. Although the effectiveness of these methods was previously assessed on different crops, to the best of our knowledge, the combined effect of these two methods on suppression of powdery mildew on lettuce growth, yield and nutrient quality has not been investigated yet.

In this study, Rodale Institute is partnering with Pocono Organics to evaluate the effect of this proposed integrated pest management approach on powdery mildew infestation over three growing seasons of lettuce. The outcomes of this project will help growers to adapt a new integrated pest management approach to control microbial diseases in their vegetable greenhouses while reduce the need for using synthetic pesticides. This can increase productivity and profitability of greenhouse vegetable production, create a safer workplace for farmers and labors, and guarantee the production of healthful food to support human health.

Cooperators

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  • Chris Belluzzi - Technical Advisor
  • Ashley Walsh - Producer
  • Dr. Dinesh Panday (Educator and Researcher)
  • Dr. Jean Bertrand Contina (Educator and Researcher)

Research

Materials and methods:

Objective 1. Determine percent reduction in powdery mildew severity on greenhouse lettuce when exposed to UV lights and MilStop fungicide compared to non-treated control

Lettuce seeds (variety Salanova) will be seeded in seedling trays containing potting soil (supplied from ORGANIC MECHANICS®). Three-weeks old seedlings will be sampled, and percent powdery mildew infestation will be recorded (considered as T0). Infested seedlings will be selected for the study.

UV-light treatment includes 1) exposing seedlings to UV-C light (λ = 100-279 nm) for 5 seconds at the intensity of 150 J/M2, 2) exposing seedlings to UV-B light (λ = 280-314 nm) for 10 minutes, 3) exposing seedlings to UV-C (for five seconds) and UV-B (for 10 minutes) together, 4) and untreated control (no exposure to UV light).

UV-lamps (Eco Pure series) will be supplied from the American Ultraviolet Company. The duration of exposure and light intensity for each UV light is selected based on previous research reporting to kill up to 90% of the powdery mildew spores (Gadoury, 2019). For the treatment with UV-C and UV-B, plants will be exposed to both UV-lights at the same time; after five seconds of exposure, the UV-C light will be shut, and we will continue with UV-B light for a total of 10 minutes. Seedling that are treated with UV-light will be kept in a dark room for a night. Transplanting will occur a day after UV-light treatment following the routine practices used by the growers at Pocono Organics.

All seedlings will be transplanted within a factorial arrangement (4*2), based on randomized complete block design (RCBD), with four replications in a greenhouse. The second experimental factor will be MilStop application with two levels (treated plots Vs. untreated control plots). In this study, 28 g of MilStop will be mixed with 2.5 gallons of water and the solution will be sprayed on plants twice with a two-week interval during the growing season of lettuce. Therefore, there will be a total of 32 plots (eight treatments replicated four times). Each plot will be 30 sq. ft which will be irrigated with drip tapes. The entire trial will be repeated three times in different greenhouses between September 2022 and March 2023.

During the growing season of lettuce, the number of plants infested by powdery mildew will be counted in each experimental unit. For the sake of accuracy, a systematic leaf sampling will be performed and the level of infestation in percent (%) on lettuce leaves will be estimated under a dissecting microscope at 40X magnification. Samples will be taken four times during the growing seasons (Table 1). Analysis of variance (ANOVA) followed by a post hoc test (Duncan’s multiple ranges (DMRT)) will be conducted to illustrate significant differences of powdery mildew infestation among treatments.

Table 1. Sampling dates for powdery mildew assessment and plant canopy prior and post MilStop applications.

Plant age

21 days

 (3-wk old)

35 days (5-wk old)

37days

 

49 days

(7-wk old)

49 days

 

56-63 days (8-9-wk old) Harvest

 MilStop Application

 NONE

1st application

 

2nd application

 

 

Sampling/Canopy Assessment Date

T1

 

T2

 

T3

T4

 Evaluate Effect

 UV

 

 UV+ one MilStop application

 

UV+ 2 MilStop applications

Extended effect UV + 2MilStop until harvest

 

Objective 2. Assess the fractional green canopy cover (%FGCC), yield and nutrient quality of greenhouse grown lettuce treated with and without UV-light and MilStop.

In this research, we will evaluate the %FGCC and compare that among treatments. Photos of the foliage will be taken four time/growing season (Table 1) and analyzed by the Canopeo app, using a Smart Phone camera (iPhone 7) (resolution of 750 pixels/inch (PPI) 326) to assess differences in foliage density. Green pixels will be counted with the program to assess the ratio of green leaves to bare soil, which is converted to a percentage of canopy cover. We will measure the yield of lettuce and compare it among treatments. Lettuce plants from the whole plot/treatment will be hand-harvested after 30-40 days from transplanting date. After recording the yield, lettuce leaves per treatment will be bagged in plastic bags and transported on ice packs in coolers to Rodale Institute for washing, cutting, and freezing at -20C. Samples will be freeze dried and sent out for mineral nutrient analysis at the Agriculture Analytical Laboratory at Pennsylvania State University.

The data will be statistically analyzed using two-way ANOVA followed by Duncan’s multiple ranges (DMRT) in SPSS Ver.25 to demonstrate significant effect of tested treatments on the crop %FGCC, yield and nutrients including vitamin C, mineral nutrients, and total sugars.

Objective 3. Establish a demonstration greenhouse with the aim of educating vegetable growers and researchers in the field of crop production and pest management.

A section in a demonstration greenhouse with a size of 4,500 sq. ft will be dedicated to replicate the research trial to demonstrate and educate growers and interested clientele on using integrated pest management techniques. This greenhouse will be managed through application of different ecologically sound approaches to produce a wide range of crop species. Application of UV-light and MilStop will be adopted in that greenhouse to manage powdery mildew infestation. We will also use this greenhouse to collect preliminary data on the effect of the developed method on different crops for yield and other pests and diseases. Rodale Institute holds several workshops on regenerative organic production of specialty crops. Pocono Organics farm and this demonstration greenhouse will serve as the host for at least one of the workshops during the lifetime of this project.

Research results and discussion:

In the first phase of this research, a UV-light chamber was built and equipped by UV-C and UV-B lamps. With the use of a UV-C meter, the light intensity (JM^2) was detected at different distances from the source of light. Based on the collected data from 14 different distances, a regression model was developed, and it will be used to estimate the energy received by the plants exposed to UV-C light (Fig. 1).

With the use of a UV-C meter, the light intensity (JM^2) was detected at different distances from the source of light. Based on the collected data from 14 different distances, a regression model was developed, and it will be used to estimate the energy received by the plants exposed to UV-C light.
Fig. 1. UV-C light intensity detected at different distances from the source of light.

We also established a dark room in the seedling greenhouse to place the UV-light chamber in it and expose seedling before transferring them to the main growing area (Fig. 2). 

We established a dark room in the seedling greenhouse to place the UV-light chamber in it and expose seedling before transferring them to the main growing area.
Fig 2. Dark room (chamber) for UV-light

In October 2022, a preliminary test was conducted on lettuce plants that were planted in growing pots. This trial was carried out in a small scale to observe the operation of developed system before running the main trial. For this purpose, lettuce seeds were seeded in a transplant tray and kept for three weeks in the seedling greenhouse. Lettuce leaves were inoculated with powdery mildew spores 48 hours before treating the leaves with the UV-C light. We detected powdery mildew on infested lettuce leaves and used the fungal material to infest the seedlings. Twelve infested lettuce seedlings were selected, six of them treated with UV-C light with an intensity of 130 J/M^2 for five seconds and six nontreated seedlings were served as the control. Seedlings were transplanted in growing pots including potting mix 24 hours post UV-light exposure. Three weeks after transplanting, we measured the fresh yield of lettuce. The preliminary results demonstrated that the plants treated with the UV-C light produced 45% more yield in comparison with non-treated plants (Fig. 3).

The preliminary results demonstrated that the plants treated with the UV-C light produced 45% more yield in comparison with non-treated plants.
Fig. 3. Fresh weight (mean ± SE) of lettuce; UV-C treated vs. non-treated plants.

In late December 2022, the second phase of this research was started with planting 1,500 lettuce seeds (variety Salanova) in seedling trays. A factorial arrangement based on randomized complete block (RCBD) was designed to implement two groups of treatment in a greenhouse: 

A. UV-Light Treatments: 

1) exposing seedlings to UV-C light (λ = 100-279 nm) for 5 seconds at the intensity of 130 J/M2 

2) exposing seedlings to UV-B light (λ = 280-314 nm) for 10 minutes,

3) exposing seedlings to UV-C (for five seconds) and UV-B (for 10 minutes) together, and

4) untreated control (no exposure to UV light)

B. Application of MilStop

Treated plots Vs. untreated control plots (28 g of MilStop will be mixed with 2.5 gallons of water and the solution will be sprayed on plants twice with a two-week interval during the growing season of lettuce)

In early January 2023, four rows of planting bed were prepared in a greenhouse and infested seedlings will be planted in those four rows (blocks). The schematic map of the trial and the layout of treatments are presented in figure 4.

The schematic map of the trial and the layout of treatments are presented in figure 4
Fig 4. Design of the trial

Soil samples will be taken on January 15, 2023, before transplanting lettuce seedlings through a systematic sampling method. 

As recommended by SARE proposal reviewers, we included a microbiologist/plant pathologist in this project. Jean Bertrand Contina, Ph.D., a director of research at Rodale Institute and experienced plant pathologist will oversee the project and help us to establish a culture of powdery mildew under a laboratory set. We keep the powdery mildew culture during the lifetime of this research, and it will be used to infest lettuce seedlings before application of UV-light.  Dinesh Panday, Ph.D., soil scientist and a Postdoctoral Research Associate at Rodale Institute also joined the team of researchers to carry out the research and outreach objectives.

 

Research conclusions:

Researchers at Rodale Institute just started this research project. The lettuce seeds were planted in late-December 2022 and seedling will be transplanted in a greenhouse in mid-January. The process of data collection will be started in late January, and the result and conclusion sections will be prepared after finishing the data analysis.  

Participation Summary

Education & Outreach Activities and Participation Summary

25 Consultations
2 On-farm demonstrations
1 Tours
1 Other educational activities: Researchers involved in this project presented information on application of UV-light to control agricultural pests and diseases in Rodale Institute Farmer Training (RIFT) program.

Participation Summary:

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

The team (scientists and the partnering grower) will have an intensive outreach plan to disseminate the results to greenhouse growers on the tested techniques. The outreach plan will include a video on the steps of performing the UV-light and MilStop applications. The video will be posted on Rodale Institute's website and YouTube to reach many viewers. A Survey Monkey survey will be attached to the video to assess increase in knowledge and potential adoption of the proposed techniques. Number of viewers will be also recorded. In addition, the results will be shared with growers at the Mid-Atlantic Vegetable and Fruit Convention in February 2024 and will be presented to greenhouse growers at the Tri-State Greenhouse Integrated Pest Management Workshop, held by University of Vermont on January 26, 2023.We will host a Field Day to share our results with growers and equip growers with information to improve vegetable greenhouse disease management. We will use other venues to disseminate our results such as a webinar, a fact sheet, a 2-hour class to new growers and veterans enrolled in a Rodale’s Veteran Farmer Training program and a peer-reviewed publication.

In September 2022 we talked about the potential of application of UV-light to control agricultural pest and diseases in organic agroecosystems in a Rodale Institute's farmer training class with ~15 attendees. We have established a demonstration site for training growers in a Pocono Organic's greenhouse and more than 10 growers have visited that place so far. 

Learning Outcomes

15 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:

We have shared information on organically sound approaches to control pest and diseases in vegetable greenhouses. We carried out the outreach objectives in Rodale Institute Framer Training (RIFT) with more than 15 attendees. We have also established a demonstration site in a 4,500 sq.ft greenhouse area. 

The topics that we educated people on:

  1. Integrated approaches to control pest and diseases in organic agroecosystems  
  2. Application of UV-light to control microbial infestation in agricultural production systems
  3.   Application of MilStop (an OMRI listed fungicide) to control fungal disease on vegetables   
  4. Organic agricultures and its effect on environment and human health 
  5. National Organic Program and OMRI's website 

Project Outcomes

1 Farmers changed or adopted a practice
1 New working collaboration
Project outcomes:

Managing pest and diseases is one of the main challenges that organic growers face in their food production systems. Pocono Organic farmers manage ~45,000 sq.ft of certified regenerative organic greenhouse space. Since we started this project, they adopted application of MilStop and UV-light to control microbial diseases in a wide range of products. MilStop application has been using to control fungal diseases on different type of vegetables in Pocono Organic's greenhouses and fields. 

Microgreens is well known as one of the most popular Pocono Organics products that can be used in Pocono Organics café or sold directly to whole and retail customers. Pocono Organic's farm manager reported the microbial diseases as the main restriction factor to scale up the microgreen production. Promising results collected from the preliminary test, encourage them to apply UV-C light to improve the yield of microgreen produced from broccoli seeds. Based on recommendations provided by Rodale Institute Scientists, they integrated the application of UV-light with Trichoderma harzianum application. The preliminary data collected from the test, illustrated that UV-light and T. harzianum have a significant effect on the yield of broccoli microgreen. Up to 200% increase in fresh yield was observed in the trays treated by T. harzianum and UV-light in comparison with the control units.    

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.