With the increasing demand for local foods across the Southeast, an increasing number of beginning, as well as experienced producers are producing vegetable crops for direct and whole sale markets. For example, in Alabama, there are a large number of producers with single or double high tunnels who sell locally at the farmers markets and on-farm retail. There are also some new farmers that have multi-bay high tunnel crop production systems who sell a variety of crops at wholesale prices.
Fueled by the increasing consumer awareness about organic foods, high tunnel producers have shifted to alternative pest management systems. In the organic farming model, pests (insects, weeds, and pathogens) are known as the yield-limiting factors that must be managed. Uncontrolled levels of pests result in over 50 percent crop loss. High tunnels not only extend the production season for the producer, but they also extend the life cycle of insect pests that may linger on longer compared to open field (check out the pest management section of the High Tunnel Crop Production Handbook). From the insect management perspective, it is extremely critical to adopt pest prevention practices; the high tunnel pest exclusion (HTPE) system is one of the best relatively-low cost pest preventive practices. This HTPE technology uses a variety of shade cloths for a relatively permanent pest prevention strategy.
In 2015, the first Southern SARE bulletin titled, “High Tunnel Pest Exclusion System: A novel strategy for organic crop production in the South” provided the basic description of the HTPE system. That bulletin described the differences between knitted lock-stitch fabric with wide openings (manufactured by Poly-Tex, MN) versus monofilament shade cloths with narrow openings (manufactured by Farmtek, IA).
That bulletin outlined the need for careful choice of these shade cloths and the basic installation process so that pests are not able to enter high tunnels and reach the crops. Researchers also hinted at the issue with natural enemy exclusion with a monofilament shade cloth with narrow openings. At that point the researchers only had a few experiences to share from on-farm research. With continued funding from Sustainable Agriculture Research & Education (SARE) coordination and Producer Grants, researchers have now made significant progress in understanding pros and cons of the HTPE system by cooperating with several producers across the state. This bulletin focuses on recent successes with pest exclusion; a separate paper will describe new recommendations for integrating beneficial insects.
Since 2014, researchers have successfully conducted several replicated laboratory studies to explore the effectiveness of 30, 40, and 50 percent shade cloths manufactured by Poly-Tex and Farmtek to stop insect pests without stopping all beneficial insects. Using small-scale models of high tunnels, the laboratory studies strongly indicated the improvement in crop quality from tightly fitted 40 and 50 percent shade cloths that excluded leaffooted bugs. Prepared with this information and additional SARE funding, the researchers approached several key producers in Alabama for on-farm evaluation of the HTPE system.
At each farm, the shade cloths were tightly installed under the rolling side-walls and also part of the end walls to keep insects away with adequate ventilation. Producers attached the shade cloths (custom-prepared by Poly-Tex) to the side walls either using grommets or stapling the shade cloth to wooden boards. The end walls were put on like a curtain and secured on the sides either with Velcro or grommets with nails. Some producers also have the fabric secured all around the high tunnel with a special door on the end-wall for entering. In all farms, the shade cloth installation was done after removing all crops from the high tunnel and pest observations were carried out on freshly planted crops. Control plots were planted outside the high tunnel. Besides direct scouting of crops, the researchers used sticky wing pheromone traps inside and outside the netted high tunnels to monitor and compare moth numbers.
Overall Findings from HTPE Studies
- A 50 percent shade cloth with wide openings (Poly-Tex) did not exclude all natural enemies tested, but slowed down or stopped leaffooted bugs.
- Major moth species with 3 to 4 cm wingspan, that include armyworms and loopers, are too large to get through a 40 or a 50 percent shade cloth. A 50 percent shade cloth can nearly eliminate them from a high tunnel. Watch for egg masses that may be laid on the fabric – remove them to reduce the chance of small caterpillars getting into the structure.
- Significant reduction in the number of squash vine borer (Fig. 6) was noticed with a 40 or a 50 percent shade cloth which should come as good news for organic high tunnel producers and market gardeners. When monitored using sticky pheromone traps, only a few male moths may be able to crawl through a 40 percent shade cloth, but those moths don’t cause any crop damage and are not able to mate with females.
- We have observed the complete exclusion of cabbage butterflies (imported cabbageworm) inside the netted tunnels on farms that routinely experienced cabbageworm outbreaks in open tunnels. HTPE systems can increase profitability of leafy green producers with a high quality crop.
- Leaffooted bugs explore surfaces really well and they can exploit any opening in the netting if it is not properly installed. A well-installed HTPE system with 50 percent shade cloth excludes most leaffooted bugs and stink bugs. Make sure to keep the fabric repaired at all times.
- FarmTek Sun Blocker can exclude many natural enemies that include lacewings and lady beetles. This may cause aphids and whiteflies to increase inside the netted tunnel. Release lacewing larvae inside the tunnel in sufficient numbers before a pest outbreak occurs. Full details regarding the integrated use of natural enemies with an HTPE system will be available in the third bulletin.
- A 50 percent woven shade cloth (with wide openings) appears to be a good choice for several common insect pest species. Install the fabric tightly under the side walls in order to allow maximum air movement. Secure the end wall fabric using Velcro or grommets that may come pre-installed with a custom-cut netting.
- Always install netting when there is no crop inside the high tunnel. Starting out clean is very important to avoid trapping insects inside.
- Take care when weeding around the fabric. Do not use a mechanical weed killer too close to the shade cloth.
- Till the soil inside the tunnel and around the border. Get rid of weeds as much as possible. These two steps help reduce grasshoppers getting trapped inside the tunnel.
- It is a good idea to limit the number of visitors entering a netted tunnel. A netted tunnel is like a greenhouse where an insect pest may accidentally enter and get trapped resulting in infestation hotspots. Insects and mites can hitchhike on clothes resulting in rapid spread.
- Readers wanting more information about the HTPE system should look for informative YouTube videos available in the HTPE Training Module on the Alabama Vegetable IPM website. It is also a good idea to integrate sorghum and sunflower trap crop systems outside the tunnel to distract sucking insect pests and attract natural enemies. Look for the trap crop training module for more information and contact the primary author for more information.
- Market gardeners can use low-cost temporary pest exclusion systems using light fabric, for example, Super Light Insect Barrier sold by GardensAlive, Lawrenceburg, IN. This and other similar fabric is very effective in the early season for protecting vegetable seedlings from aphids, flea beetles, and grasshoppers.
- Always contact the Cooperative Extension Service in your state and county for proper pest identification before developing a site-specific IPM plan suitable for your farm or garden.
Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America’s Southern region. This material is based upon work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, through Southern Sustainable Agriculture Research and Education, under sub-award numbers: UGA-RD309-134/S001163, UGA-RD309-129/S000826. USDA is an equal opportunity employer and service provider. 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.