The effect of row cover and pesticide application variable timing on pests in organic vegetable

One challenge of organic farming is to sustainably prevent the establishment of damaging pest populations. Two ways of achieving this goal include the use of row cover and organic pesticides. However both methods can cause potential problems for growers; row covers prevent pollinators and natural enemies from accessing the crop, while pesticides may eliminate natural enemies that would otherwise keep pest numbers in check. The efficacy of both approaches may also be impacted by the timing of their application, such as if they are used sporadically or continuously. To understand how these two organic farming practices impact pest populations and the damage they inflict we investigated the independent and interactive effects of row cover and organic pesticide application timing. We measured pest (squash bug) and natural enemy density in four treatments applied to a field-planted squash crop; (1) row cover until anthesis and no organic insecticides; (2) row cover until anthesis and organic insecticides applied weekly until harvest; (3) row cover until anthesis then replaced one week later and application of organic insecticides directly before covers are replaced; (4) row cover until anthesis then replaced one week later and no application of organic insecticides. We found that row cover and organic pesticides suppress both pest and natural enemy numbers, the strength of this effect depends on the timing of their application, and that these effects are interactive. Our results suggest that to fully realize the benefits of organic farming strategies and maximize the sustainability of such methods the timing of their application and combined effects must be considered.