Alabama researchers find pest exclusion system that allows for natural enemies

From IPM in the South by Rosemary Hallberg

by Ayanava Majumdar, Alabama Cooperative Extension System

The concept of High Tunnel Pest Exclusion (HTPE) system has been explained in many other articles listed at the end. Basically, pest exclusion is a feasible IPM strategy where a sturdy structure can be modified with fabric to serve as a barrier between insect pests and host plants. HTPE can be very an effective strategy for organic and conventional high tunnel producers that aim at preventing insect pests. However, the HTPE system raises questions about the unintended consequences of this technology, such as the exclusion of natural enemies. With this in mind, we conducted laboratory-based assays to evaluate natural enemy exclusion using HTPE models fitted with 30, 40, and 50 percent shade cloths sold by Poly-Tex (MN), Grainger (IL), Green-Tek (WI), and Farmtek (IA). HTPE models were covered in glass cages during the tests. Farmtek shade cloths have fine openings (knitted monofilament) whereas the shade cloths from other vendors have wide (v-shaped) openings. 

Overall findings and IPM recommendations:

  • Shade cloths caused significant reduction in the movement of natural enemies, especially green lacewings. A 30 percent shade cloth with wide openings did not affect lacewing migration; however, a 50 percent shade cloth can exclude or severely slow down lacewings.
  • Lady beetles are smaller than lacewings and better able to move through 30, 40, and 50 percent fabric with wide openings (vendors: Poly-Tex and Green-Tek). However, a 50 percent shade cloth by Farmtek completely excluded lady beetles due to the finely woven structure.
  • Past studies with leaffooted bugs have indicated a 50 percent shade cloth with wide openings (Poly-Tex) to be best for pest exclusion. The new finding regarding natural enemies reported here also indicates a 50 percent Poly-Tex fabric to be favorable to lady beetle migration. Currently we are evaluating the 40 and 50 percent shade cloths in commercial high tunnels to corroborate these trends.
  • Producers using 40 or 50 percent shade cloths for pest exclusion can use commercial natural enemies such as green lacewings and release them as soon aphids are detected in order to take advantage of the HTPE system.
  • Readers wanting more information should look for some informative YouTube videos about the HTPE system at the Alabama Vegetable IPM website. Producer testimonials are also available in the HTPE Training Module. Always contact a commercial horticulture regional Extension agent for proper insect pest identification and developing a site-specific IPM plan.
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