Spore Exclusion - A New Approach to Downy Mildew Prevention in Cucurbits

Final Report for FNE09-664

Project Type: Farmer
Funds awarded in 2009: $8,541.00
Projected End Date: 12/31/2009
Region: Northeast
State: New York
Project Leader:
Louis Lego, Jr.
Elderberry Pond
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Project Information

Note to reader, attached is the complete report for FNE09-664 with photos

With this project we set out to prove that the new strain of downy mildew that has seriously impacted organic and sustainable cucumber production through out the eastern United States could be controlled using a method we called Spore Exclusion. In carrying out the project we tried several methods to exclude DM spores from reaching and infecting actively growing cucumber and melon crops. To track the movement of the disease from the mid Atlantic States we used the North American Plant Disease Cucurbit Downy Mildew Forecast managed by NC State University. One of the spore exclusion techniques we tested proved to be 100% effective, even under severe disease pressure. This technique used a poly tunnel that was placed under a slight positive pressure with air that was filtered to exclude the DM Spores. We believe the project has opened the door to a new sustainable disease prevention technique applicable to many crops. This technique requires no sprays and has almost no chance of losing effectiveness due to disease mutations or resistance to chemical treatments.


Farm Profile and Participants

Elderberry Pond is a 100 Acre Certified Organic Farm located in the Finger Lakes Region of Upstate New York. We produce a wide variety of fruits, vegetables and pasture raised meats. My wife Merby, and my son Christopher and I operate the business on a full time basis. We have operated the farm for about 27 years.
Our focus at Elderberry Pond for the past twenty seven years has been to introduce customers to the best tasting fruits, vegetables and pasture raised meats available. We have done this through our country food store, through a CSA, and farmer’s markets, and most recently through “The Restaurant at Elderberry Pond.” In all of our market venues we emphasize the important role that varieties, or breed play in the quality of our offerings. It is for this reason the continued production of sweet melons and cucumbers on our farm is of such importance.
Another aspect of the farm that is important to this proposal is our emphasis on on-farm research. We have carried out many farm based research activities on the farm over the past 20 years including several funded by SARE. A number of the projects, like this one, involved innovative technical approaches to agricultural problems. For example we built a small scale computer controlled flash pasteurizer that could be used by small apple growers when pasteurization became mandated by the State. This effort was funded by NYS Ag and Markets.

The participants in the project included myself as designer and builder of the enclosures, my son Chris who helped with the fabrication, and our technical advisor, Abby Seaman, from the New York State Integrated Pest Management Program at Cornell’s New York State Agriculture Experiment Station.

Project Objectives:

The goals of this project are as follows:

1. Design and build three enclosure types that can be tested to determine if they can prevent Downy Mildew Spores from infecting healthy cucumber plants during the peak of the infection season.

2. Follow the progression of Pseudoperonospora cubensis disease spores from cucurbit fields in the southern and mid Atlantic States using the forecast from the North American Plant Disease Center at North Carolina State University.

3. Plant several standard and disease resistant varieties of cucurbits in the enclosures and in uncovered control plots at a time to allow the plants to be at a vulnerable state when the spores are likely to be present in our area.

4. Monitor the plants and record any infections that occur in both the control plots and in the spore exclusion enclosures.

5. Determine which, if any, of the enclosures prevent infection.


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  • Abby Seaman


Materials and methods:

During this project we tested three types of downy mildew protection closures. These were:

1. High density row covers.

2. High density row covers treated with an organically approved contact fungicide.

3. Poly tunnel with filtered air flow.

Row covers for spore exclusion
Two of each of the two types of row cover closures were tested, one planted with netted melons and one with cucumbers. A planting of each crop was made during the summer when spores are predicted to be in the area. With each planting a non-enclosed “control” planting was done using the same varieties (see diagram below)
The row cover approaches (1 & 2) used commercially available row covers that were evaluated and carefully sealed around the perimeter. The covers were left on at all times during the seed germination and seedling growth. At bloom the cover from the netted melons was removed during the daylight hours and at times when spore movement is least likely. This will permit pollination. During these periods an organically approved fungicide will be sprayed on the plants. During periods of mist or damp cloudy periods the row covers will be kept in place. These are also the times when pollinating bees are least active.
For the treated row covers an organically approved fungicide, Milstop was used. Initially the row cover was soaked in a solution of Milstop. Later applications were applied to the row cover while in place. The amount of fungicide applied was approximately the amount labeled for the crop beneath the cover. The idea was to enhance the protective properties of the cover by killing spores that contact the cover.
For the cucumber plantings we used seedless (parthenocarpic) varieties which require no pollination. This allowed us to keep the covers on throughout the harvest. In all test beds drip irrigation was used.

The varieties of cucumber and netted melons evaluated were as follows.

Cucumbers: Diva, Tasty Jade, Tyria, Suyo Long

Melons: Early Champ, Sarah’s Choice and

Row cover selection:
A number of row covers were purchased and examined for fabric uniformity and quality. The DuPont Ag 06
had the best uniformity and tightness of weave, and was used for all the beds among the row covers AGRIBON AG15,DuPont Ag06 and Pro 17 Agrofabric.

The bed sides for the row cover tests were made from 16 inch concrete blocks that were set carefully in a few inches of soft soil. The beds were filled with a combination of good soil and compost. A small amount of a slow release Fertrel fertilizer was added to each bed. The row covers were held down to the blocks on the side by boards.

Poly Tunnel for Spore Exclusion
The low poly tunnel approach was a bit more complex. As the photo at the right shows, it was fabricated from four -13 foot hog panels that were connected with zip ties at the top. The structure was 26 feet long and approximately 4 feet high. Along the top we tied 1 inch foam pipe insulation to prevent the structure from tearing the plastic, which was to be placed over the wire structure. At the near end of the tunnel is the fan/filter enclosure which will be discussed in detail below. The photo at the right shows the two row cover test beds on the right of the poly tunnel. The control bed with no covers is just to the right and in front of these beds, but cannot be seen in this photo.

The photo at the right shows the fan and filter enclosure. The purpose of the fan was to pull in air in through the spore filters and to put a slight pressure on the tunnel. The positive pressure insured that any leaks in the enclosure would not draw non-filtered air into the enclosure. Even when the bottom of the enclosure was lifted to harvest cucumbers, air would flow out…not in!

The fan selected was a two speed 1/30th horsepower model GP designed for greenhouse applications. It had shutters which in this photo faced the inside of the enclosure. We installed a temperature controller, but in retrospect this would not have been necessary, since to maintain positive pressure on the enclosure it was necessary for the fan to run all the time. It also became apparent that a smaller fan would probably have been sufficient.

The filters used were standard furnace filters. They were two 20” by 20” “Filtrete Max" Allergen reduction filters (top and bottom) used on the inside layer and two standard dust filters used as pre filters on the outside. The maximum allergen filters are capable of blocking particles less than 0.5 microns. The 3M MPR( micro particle rating) rating of these filters is 1500 and the MERV ( minimal efficiency rating performance value) was 13. The filters use electrostatic media to block very small particles. The cost of the allergen filters was less than $20 each at Lowes Home Improvement.

Once constructed the tunnel was covered with standard
4 mill greenhouse film. As shown at the right, the film
was attached at the ends using wide Velcro strips and at the bottom, along the length of the tunnel, using flexible plastic lumber. There were several folds of the plastic film along the cement blocks to form a seal. Again, because of the positive pressure in the enclosure small leaks were not important in keeping out spores.

Determining the optimum time for planting the cucumbers and melons in the enclosures was tricky. I wanted the plants to be established, but if the infection came late, I wanted them to be still in the rapid growth stage.
We decided to plant all the cukes and melons on July 1st and 2nd. To monitor the disease progression in the Northeast we used the North American Plant Disease Forecast Center Cucurbit Downy Mildew forecast at the NC State website (www.ces.ncsu.edu/depts/pp/cucurbit). The forecast was checked every two days or so and the disease progression was followed from sources in Virginia and North Carolina through West Virginia, Pennsylvania, southern NY and eventually in late July into our area. The first warning of DM spore transport and possible infection was on July 22nd. As it happened there was no evidence of DM disease presence until nearly three weeks later on August 18th. The timing was nearly perfect, as the plants were blooming, with some small fruit and were growing very rapidly.

Research results and discussion:
Results, Conditions and Economics

The results of the project were clear and dramatic. In late August the spores from a southern wind were carried to ground at our location by a steady, light rainfall that lasted several days. The impact on the plants was first seen on both control plantings (melons and cucumbers) but was more severe on the cucumbers. The picture below shows the cucumber plants at an early stage of infection.

At the same time there were signs of infection on the un-treated row cover cucumbers, see right. At this time and for about ten days, the plants under the row covers treated with Milstop showed no sign of infection. Then by August 27th there were signs of infection on the plants covered by the treated row covers.

During this entire period of time there were no signs of any infection in the filtered air poly tunnel, even though it was located just two feet from the other infected plantings!

The results with the netted melons were very similar to the cucumber results, only about three weeks later. The control planting was infected first, followed by the untreated row cover and then about ten days later by the treated row cover.

On September 2nd Abby Seaman, our technical advisor, visited the project. At that time the row covers had were about to be removed from the control and row cover beds and the poly tunnel was still covered. There was still no sign of PM in the poly tunnel. The following week, the row covers were removed.

The following week all the beds except the poly tunnel were tilled and replanted in fall lettuce and greens. In spite of being surrounded for several weeks by infected cucumber plants, there was no sign of PM in the poly tunnel, and harvest of cucumbers continued on a daily basis. At that time the poly tunnel cover was removed. We had shown that a poly tunnel when filled to a slight positive pressure with air filtered by a standard furnace filter would exclude spores of Downy Mildew, and prevent plant infection.


The disease conditions during this summer of 2009 were about as bad as we had ever seen on our farm in 30 years. This was due to very wet weather throughout the growing season. In discussions with other farmers in the area the problems with Downy Mildew were about the same as in previous years, but perhaps started a bit later in the season.


The impact of growing certified organic cucumbers or melons in high tunnels with filtered air would certainly cost more than growing them in open fields as we have traditionally done. The problem is, of course, that that appears impossible to do with the new strains of Downy Mildew and with the limited organic spray options we have. I do believe it will be possible to design a high tunnel with minimal additional cost that could provide spore exclusion and that growing organic cucurbits in these tunnels will be profitable.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

During the summer we had farm tours for people interested in organic farming every Sunday afternoon. On all of these tours we explained the project and showed the progress we were making. We also conducted about five special tours for interested gardening groups and extension staff. In December we are presenting the project results to the organic working team at Cornell. In February we are presenting a workshop on the project at the PASA meeting at Penn State and have been ask to present a paper at the NOFA-NY conference in 2011. I am sure there will be many other outreach opportunities over the next couple of years. For example, we are presenting two papers this year on our SARE 2007 Apple Evaluation Project.

Project Outcomes

Assessment of Project Approach and Areas of Further Study:

What I would like to do is to pursue additional funding to design and construct a practical size, power-efficient spore exclusion tunnel on my farm, and to test the effectiveness of the idea on cucurbits and other crops on a larger scale. I realize that the funding source must be able to pay for some capital expenditures as well as labor, and so I am not sure where I can get the funding to continue. I am now convinced that this concept will be important to sustainable fruit and vegetable production.

Potential Contributions


I think the fact that we know simple mechanical spore exclusion works, is a major step forward. What we need to do now is to access what other crops this will work for (tomatoes, raspberries etc) and to design either small enclosures or large high tunnels that will work with minimal power inputs. The idea of using heat draft towers or solar fans for air movement through the filters needs to be investigated.

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.