Crop diversity has been repeatedly linked to increases in the abundance and diversity of natural enemies in agricultural systems, but how to use this knowledge requires additional information. For example, evidence suggests grain sorghum production contributes large numbers of generalist predators to cotton fields. However, studies of possible benefits have been confined to adjacent fields of these crops. To maximize the benefits to cotton production, the scale of predator enhancement and specific factors influencing predator abundance in cotton should be determined.
To examine the effect of grain sorghum on cotton predator abundance at the landscape level, direct manipulation is logistically and financially prohibitive. Therefore, we elected to use natural variation in agronomic and landscape variables in cotton production as a “natural experiment.” Maps of agricultural fields across three counties in Texas’ Southern Rolling Plains were generated using GPS technology, while data on abundance of predators and pests were collected from 70 cotton fields throughout the area. Additional information on cultural practices was gathered from cooperating cotton growers in all fields studied.
Separate regressions were conducted on data from three dates corresponding to stages of crop phenology. Data on pest abundance, cultural practices, and landscape variables were treated as independent variables, while predator abundance was used as the dependent variable. Results were examined for evidence of large-scale benefits of grain sorghum on cotton predator abundance and possible methods to increase this effect.
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