This project was designed as an experiment to retrofit existing high tunnel structures used for growing vegetables with a woven shade cloth material. The hypothesis was that the shade cloth could act as an effective bug screen without completely restricting air flow and ventilation. Our farm had an existing high tunnel that we used for the experiment. The results of the study were very promising and we feel that this method has applications in the future of the small farm.
Local Appetite Growers is a small polycultural farm in Baldwin County Alabama – right along the Gulf Coast. Utilizing high tunnel production, field production, and hydroponics our farm grows food crops for the local restaurant and farmers markets. Facing intense insect pressures of the coastal environment, this study was an experiment in a mechanical method of screening pests from valuable food crops grown inside of high tunnel structures. This mechanical screening was achieved using a woven shade cloth material retrofitted to existing high tunnel structures. The results of the study were promising for the use of this material and methodology as a way to reduce the use of pesticides in vegetable production in the South.
Insect pressure is one of the major challenges of vegetable production in the deep south. Heavy and repeated applications of pesticides are not only expensive and time consuming to the farmer, but is also much less desirable by the end consumers and the environment. Fresh market produce is expected to be visually blemish free with insect damaged produce fetching a lower price or not selling at all. This is a challenge to growers in the Gulf Coastal South where bug pressure starts early in the Spring and persists late into the Fall because of warm weather and plentiful moisture – many insects have another entire life cycle along the Gulf coast than those just a few hours inland.
Seeking an alternative to repeated pesticide applications, this project sought a method of mechanical exclusion of insects inside of an existing high tunnel. After researching net houses and screen houses, it was deemed that most bug screens available were limited in that there was a major reduction in airflow inside of the structure because of the fine mesh of the bug screens. Heat and humidity buildup inside of these structures was a major issue, and often led to disease, fungus, and mold outbreaks. Realizing that for the crops that our farm produces were mainly affected by larger body insects including moth caterpillars, stink bugs, leaf-footed bugs, and the various cucumber beetles and other beetles – we sought a material for screening that would exclude the larger body insects but still allow for adequate airflow and passive ventilation.
The idea for using woven shade cloth as a bug screen started to seem possible. We had noticed the effectiveness of the shade cloth as a bug screen on one of our tunnels by accident. We had an oversized piece of shade cloth with the extra portion hanging along the west wall of the high tunnel (adjacent to the roll up side walls). We noticed leaf footed bugs piling up on the outside of the shade cloth trying to get to the crops inside. The idea of a hybird high tunnel was born. We used our existing high tunnel and fitted a 50% woven shade cloth to the endwalls and sidewalls between the base boards and the hip boards of the structure.
For this study we proposed growing Spring season tomatoes on the inside of the structure versus a control crop of tomatoes grown on the outside of the structure. For the Fall season we used sugar snap peas as our test crop.
The objective of this study was to test the use of woven shade cloth for a bug screen material in simple high tunnel growing structures. With the intense insect pressure along the Gulf Coast, regular pesticide application is necessary to produce quality vegetable crops for market. This is an expensive, time consuming and environmentally questionable practice. We sought to try to reduce pesiticide usage by the use of mechanical screening system.
Similar net house studies have been performed but many of the studies used fine meshed bug screening products that severely limited airflow and ventilation. Traditional bug screening products are designed with small mesh size to exclude all small bodied insects including whiteflies and thrips. Since our target insects were larger body insects such as moths, stink bugs, squash bugs, and various beetles – we felt that the use of a larger meshed materials would help to solve the problem of airflow and ventilation.
The methods that we used to test the idea of using shade cloth as an insect screen were to grow a test crop of tomatoes inside of the retrofitted high tunnel and growing a control crop of the same tomatoes in the field nearby. The tomatoes were planted in the high tunnel and in the field at the same time. The next step was to fasten the 50% woven shade cloth to the high tunnel structure between the base boards and the hip boards – this was the area that was open when the roll-up sides were rolled up. We also fastened a large panel of woven shade cloth for endwalls on each side of the structure. A large heavy duty zipper was used for access in each end of the tunnel. As the tomatoes grew and insects began to show up, we monitored the insect pressure and damage on the test crop versus the isect presence on the control crop (field crop). We took physical counts of the insects in each row as well as weighing in the total insect damaged harvest to determine amount of crop loss due to insects.
-Difference was immediately noticeable, inside tunnel we were losing only 10%-20% of big tomatoes to bugs – outside tunnel we were losing 80%-100% in June and July
-Does get hot in tomato house, over 100 degrees some days
-Pollination does not seem to be affected – have had some blight issues
-Biggest difference came about a month after installing screen (late June) – 135 caterpillars on one outside row of tomatoes, 3 caterpillars on one row inside tomatoes
– Cherry tomatoes in field had less loss 30%-40% loss versus less than 10% inside tunnels (numbers were based on weight of marketable fruit harvested)
-Squash bugs infiltrated and started breeding inside -they remained inside of screen tunnel, we had to kill several generations inside of the tunnel.
-For the Fall crops the difference was less marked – We planted sugar snap peas on the outside of the tunnel and a control crop in the field. We had some armyworm problems on sugar snap peas when they were young, but an early cold spell in October seemed to have eliminated most of the caterpillar pressure in the fields. No fall caterpillars made it inside of the structure.
– The 50% shade cloth was effective against cucumber beetles as well, although these showed up on field (control) crops after majority of damage had been done by caterpillars. We found several in the field crops but none were present inside of structure.
-We were late to install screen on high tunnel (early June) some bugs got in already – leaf footed bugs began breeding inside of structure later in the season and the structure kept them trapped inside of the screen – this was a real problem – they had to be removed primarily by hand. Timing is critical.
-Moths laying eggs all over screen – young caterpillars can fall inside of screen and get to plants – Dr. A noted this same issue in his net house study
-Exclusion of good bugs (ladybugs, lacewings, mantis) but dragonflys still get in- somehow
-Small bugs still get inside and are hard to control (flea beetle especially) – Aphids were also present on some plants inside of structure
-Screen is expensive +/- $1000 to install screen on 30’x100’ tunnel
-Have to customize design to particular tunnel design – our end walls that were ordered did not quite fit right and we had to improvise screening at the bottom of the panels. There are no ready made kits for this.
-Although ventilation is good – airflow still restricted, need fans and misters to get proper airflow and cooling on hot still days
Educational & Outreach Activities
We have been participating in various outreach events to share our experience with other farmers. The first outreach event was hosting a farm tour for the 2015 SSAWG small farm conference held in Mobile, AL on January 15 of 2015. We had approximately 30 small farmers, extension agents, and academics from the conference attend the tour and we walked them through our high tunnels and discussed the project with them. In February of 2015 this project was presented at the 2015 Alabama Fruit and Vegetable Growers Conference in Auburn, Alabama. I presented the project titled (Hybrid High Tunnel Production) as one of the educational sessions at the conference.
Dr. Ayanava Majumdar from Auburn University Extension Agency has included some of the data and methods from this study in his work on his “High Tunnel and Pest Exclusion System” in the SARE bulletins and in his monthly publication entitle “Alabama IPM Communicator”
SARE and Dr. Majumdar will be visiting our farm on April 29 to take video footage of the farm to use in online SARE resources for pest management.
With this study we feel that we have found a way of dealing with some of the insect pressure on
high value food crops and an alternate to repeated pesticide application. While there are costs involved in the structure and the screening materials, we feel that the multi-year long life expectancy of the equipment and potential to get at least 2 seasons per year makes this method a cost effective method of pest control. The alternative insect control is repeated spraying of pesticides during the season. This can be multiple times per month during the summer months. When added with the cost of the pesticide, the labor to do this repeated spraying can be a considerable cost.
This method has potential for small farm enterprises and especially those trying to grow organically or pesticide free produce. We think that this method of insect exclusion could have very beneficial effects for the small farm industry in the South and other areas with heavy insect pressure.
More study could be done on the cost effectiveness of the structures that we have created, including the cost of the high tunnel, to see how long it would take a hybrid high tunnel like ours to pay for itself. The up front costs of building a structure like this is probably the most limiting factor to growing with this system.