- Vegetables: cucurbits, tomatoes
- Crop Production: food product quality/safety
- Education and Training: extension, farmer to farmer, on-farm/ranch research
- Energy: solar energy
- Pest Management: cultural control, disease vectors, integrated pest management, physical control, prevention, sanitation, weather monitoring
- Production Systems: organic agriculture
- Soil Management: soil analysis, nutrient mineralization, soil quality/health
- Sustainable Communities: sustainability measures
New strains of highly resistant downy mildew (DM) spores travel to the Northeast in high altitude
clouds and destroy many cucurbit crops. In 2009 we received a NE SARE Grant to prove a concept
we called “Spore Exclusion” It was based on the idea that a simple high efficiency furnace filter
could block the spores. We built a 30’by 5’ tunnel with a small fan and a filter on one end (figure
1). We planted cucumbers in the tunnel, and in beds around the tunnel. When the spores reached our
area, all of the non-enclosed cucumber and melon beds were destroyed FIG 2 and NONE of the
plants in the exclusion tunnel were harmed FIG 3. The reported results brought a high level of
interest from growers & researchers. The question that was asked is whether or not the concept
could be made to work in a full size high tunnel or hoop-house. In this proposed project we would
design and demonstrate modifications to a standard 26 X 96 foot tunnel that would exclude DM
(and potentially other) spores while maintaining acceptable tunnel temperatures and allowing for
easy access for care and harvesting. I believe the demonstration of this novel concept at this scale
would permit the production of these crops (and potentially others like tomatoes) without the use of
any fungicides regardless of the resistance of the variety! We would make available the tunnel
design modification details to the university researchers and to growers.
Project objectives from proposal:
This project will be accomplished in four phases, which are described in the following paragraphs and
1.Design Required Tunnel Modifications – Based on the prototype low tunnel demonstrated in 2009 and 2010, determine what modifications to a standard 26’ x 96’ (Rimol Northpoint) tunnel must be made to exclude
disease spores while allowing free entry and the proper environment for plant development and growth
(temperature, humidity and air replacement)
2. Procure the Basic Tunnel (not charged to the grant)
3. Procure parts required for spore exclusion modifications
4. Erect the spore exclusion tunnel
5. Construct raised beds, fill, and install irrigation & trellising. Plant the tunnel with cucurbits and other crops
impacted by external sources of disease spores. Also plant control plantings of the same crops in new beds in the
immediate vicinity of the tunnel and in our existing tunnel without spore exclusion
6. Install data recorders and begin data collection.
7. Prepare reports and material for outreach
Task 1. Design of Required Tunnel Modifications
Many tunnel design requirements were worked out on the 2009 prototype tunnel. For example, the filter specs necessary to block the spores and provide good air flow. We learned that the enclosure need not be perfectly sealed if a very slight positive pressure is maintained, so that air goes out of leaks rather than comes in. Perhaps the most amazing lesson coming out of the prototype was the tremendous cooling effect of Evapo-transpiration from leaf surface area within the tunnel. In this effort we must apply what we have learned to an enclosure of nearly 60 times more volume than the prototype, and to allow for a entry door design that will not allow entry of spores. In some ways a larger enclosure is an advantage.
For example more air volume means more temperature and humidity stability. The additional height of the high tunnel over the prototype provides creates temperature stratification, where-in the hot air can be removed from the top of the tunnel using a hot air collector and one way vent. It is important to remember that the tunnel can be operated in a normal mode (sides rolled up or down, doors open etc for much of the summer. It is only necessary to switch to the spore exclusion mode when a disease infection period is eminent. This would be when the Downy Mildew Forecast Model predicts an infection in the area or where there are others indications on outside plantings that an infection is underway or likely.
The design modifications to a standard tunnel will include:
1a. Estimate of air flow through the tunnel that is required to keep the temperature at or below 100 deg F. Factors that will influence this are planting density, particularly in the vertical dimension i.e. trellised cucumbers, tomatoes etc. The higher the total leaf surface in the enclosure the cooler the interior will remain, assuming there is enough irrigation water to prevent wilting. New IR Tunnel film type may also impact the heat inside the tunnel. Commercial greenhouse cooling companies provide tables to help in these calculations.
1b. Design and layout of the positive pressure ventilation system. Sizing, and placement of the pressurizing fan and filters. Air exit volume must be slightly less than input volume to maintain approximately .05 inches of mercury positive pressure in the tunnel.
1c. The entrance way to the tunnel must be through a double door pass-way so that no outside air is likely to enter during an infection period.
These modifications should not impact the cost of a new tunnel by more than 10 percent, an important factor in the feasibility of this concept.
Task 2. Procure the basic Tunnel
We started this proposal with the idea of modifying our existing tunnel for the spore exclusion mode, but realized that the conversion process would be too disruptive to our early spring plantings in that tunnel. We decided to procure a new tunnel for the test with the idea of using the new tunnel to grow disease sensitive crops and to continue to research spore exclusion with other crops. It also gives us the important advantage of having the old tunnel as a control planting for this project.
Task 3. Procure Parts for Spore Exclusion Modifications
The fan and filter mounts, exit air ducts and double door entry will be fabricated from standard hardware store items and assembled with the tunnel. A rough sketch of the proposed tunnel with modifications is shown in FIG 6.
Task 4. Erect Tunnel With Spore Exclusion Modified End Walls and Indoor Ridge Venting System
Task 5. Set up Indoor and Outdoor Raised Beds, Fill with Soil and Plant all Test and Control Beds
The tunnel will be planted in longitudinal beds about 90’ long. The center bed will contain several varieties of parthenocarpic cucumbers. In the side beds we will plant heirloom tomatoes and other disease susceptible crops to see how they fare in this environment. A real upside of this spore exclusion concept would be if it can be extended to other crops. All crops will be trellised to fill the volume of the tunnel to the greatest extent possible, as discussed under temperature control. Examples are shown in FIG 7. The control beds located in the vicinity of the tunnel and in the existing tunnel, will be planted with the same crops. Soil tests will be conducted in all test and control beds. Irrigation tape will be used in all beds, as sufficient low salinity water is essential for good plant evapo-transpiration cooling.
Task 6. Set Up Monitoring and Recording System
Monitor and record the movement of spore clouds using the NC State model and disease rating protocols developed by Meg McGrath at Cornell. Abby Seaman,our technical advisor on this program and on our prototype grant, will also be available to help us with disease identification and recording.
Measurement of Results
For better or worse, the results of a test that aims to prevent downy mildew in cucurbits are dramatic. As seen in figure 2, when downy mildew spores reach an area of the northeast the cucumber, melon and now winter squash plants die within days. If the spore exclusion high tunnel works, we will know within days of the first infection period. There are, however, other practical issues with a spore exclusion high tunnel that must be measured and evaluated and this will take more careful monitoring and measurements. We would like to know if the plants grow and produce as well in the spore exclusion house (prior to an infection). The issues of practical importance that should be measured and recorded are:
Tunnel Temperature Control
Can the tunnel maintain acceptable temperature control during hot days of a spore infection period? During heat stress the plants which will be trellised high in the tunnel to help cool the airspace will require sufficient water to encourage the high rate of leaf evaporation to help cool the airspace. The rate of evaporation from the leaf surfaces depends on the difference between the relative humidity at the leaf surface and that of the air in the hoop -house. If the air in the hoop-house gets saturated, evaporation will decrease or stop and heat in the house will increase. This is why it is important to measure the relative humidity and the airflow. We will record the temperature and humidity in the tunnel using small omega data loggers. These battery operated data loggers record temperature and humidity every 10 minutes for several days and download plots to a pc for observation. They are inexpensive (about $50) and will be used at several locations in the tunnel. We will also measure the amount of filtered airflow required to keep the tunnel at a temperature of less than 100 deg. F. The temperature/
humidity conditions in the low tunnel we used for the prototype was not a problem and we are encouraged by this, but we need to do these measurements to come up with design requirements for future spore exclusion tunnels.
Crop Health and Yields
It will be important to compare the health and yields of cucumbers (and other crops) grown in the spore exclusion tunnel with those in our standard tunnel. We will do this by monitoring and recording plant growth, leaf conditions, and the yields of crops grown in both tunnels. We will do soil tests in both tunnels to insure that meaningful comparisons can be made. A data log will be maintained containing weekly growth of the cucumbers in the spore exclusion house, in the standard house, and in the outside control beds.