The USDA stated that 21.2% of households in Arkansas experienced food insecurity in 2013, compared to 14.3% nationally. Johnson County in Arkansas was also designated as a “food desert”, in which households lack access to fresh, healthy, and affordable food. Community gardening in Johnson County is an attempt to mitigate this food shortage and a source of income for others. Gardening is also an educational opportunity for students and the community.
Garden pests are often controlled using toxic pesticides. Alternatives such as Integrated Pest Management (IPM) using natural enemies to protect crops may be a viable alternative. Natural enemies may prefer diverse plant habitats with architectural complexity compared to simpler habitats, making IPM more effective. We determined the influence of plant diversity and complexity on IPM in a garden setting. Plantings of Swiss chard acted as our monoculture treatment and plantings of Swiss chard, tomato, kale, and beans were our polyculture treatment. In addition, we added barriers of green manure (Bermuda grass) to create more complexity compared to standard mulch. We calculated species diversity and examined herbivore abundance. We also recorded chlorophyll fluorescence and content, and plant yield to document changes in plant physiology.
Results/Conclusions
Preliminarily, we found that polyculture and green manure had the greatest effect on arthropod diversity and natural enemy abundance. Overall, there were more arthropods in polyculture and green manure plots compared to monoculture. Unfortunately, this also included crop pests such as aphids. Sharpshooters were more abundant on monocultures of Swiss chard compared to polyculture Swiss chard. Spider abundance, was greater in polyculture plots compared to monoculture, suggesting a recruitment effect of habitat complexity on spider abundance.
In contrast to the arthropod data, yield was greater in monoculture plots for Swiss chard compared to polyculture. Polyculture plants with the mulch treatment had greater yields than their green mulch counterparts, suggesting shading may have been a factor for reducing yields. Chlorophyll data was comparable between treatments. Our results suggest several trade-offs between increased habitat complexity and plant architecture and simpler, monoculture environments. With our results, gardeners using polyculture and green manure should expect more herbivore pests on their plants, but greater natural enemy activity may neutralize the increased herbivore abundance. Ultimately, the combination of green manure may have reduced yields through shading and competition between plants.