The use of cover crops provides both direct and indirect benefits to agricultural ecosystems. Cash crops sown after cover crops directly benefit from better nutrient availability, increased moisture retention, and improved weed suppression. Although there is some evidence, we still lack a complete understanding on the effects of cover crops as an insect herbivory suppressor, and the mechanisms that mediate these effects, if any. To test this, we planted two commonly used leguminous cover crop species, sunn hemp, Crotalaria juncea, and cowpea, Vigna unguiculate in an organic farm in South Texas and observed their effectiveness in providing pest management while also attracting beneficial insects. Data was collected on plant height, insect damage, and plant biomass, in addition to insect community composition in the field. Our preliminary results on cover crops suggest that sunn hemp performed significantly better in all measures, and continuously showed significantly lower pest damage (caterpillars, true bugs, and aphids) along with a high prevalence of beneficial insects (Coccinellids, wasps and bees) when compared to cow pea. Sunn hemp also improved (higher species richness) the surrounding insect community in the area and thrived in the summer heat without much resource input.
The specific objectives of this project were to:
- Determine the impact of cover crops on the tri-trophic interactions of insects in organic vegetable systems.
- Determine the weed suppression potential of cover crops in organic vegetable systems.
- (Educator and Researcher)
Cover crops were planted in a certified organic farm in Edinburg, TX during the summer of 2018. We collected information on: cover crop height, insect damage, cover crop biomass and weed biomass. We also collected insect samples in the cover crop treatments. Cover crop height was measured using measuring tape from the base of the plant, not including roots, to its tallest point. Damage was assessed using a visual scale of 0 (no damage) to 4 (extensive damage, little of the plant remains). From the visual insect damage estimation we determined the damage caused by insect pests. Cover crop biomass was collected just before cover crop termination. Cover crops were harvested and oven dried for 48 hours and total biomass for each cover crop type and weed was estimated. Flying insects in the cover crops were collected using the sweep net. We also estimated the pest damage in cash crops following the visual damage scale recording. Insects in the cash crops were collected using a sticky trap and pitfall traps.
Our results indicate that cover crops support beneficial insects during the early summer season, while the time of growing season does not affect herbivore abundance. Crop-specific effects were found for herbivore abundance with possible cascading effects on insect community as well as damage levels on the subsequent cash crop, but without any impact on the growth traits of the cash crop. Similarly, our results also show that cover crops reduced the weed biomass. When followed by subsequent cash crops, the weedy fallow plots had significantly higher weed biomass. Sunn hemp was most effective in weed suppression. Overall, our results indicate that cover crops, especially those with the ability to grow quickly and develop a closed canopy or known to have allelopathic properties, have the potential to control weeds in organic vegetable farms in semiarid subtropical Texas.
Educational & Outreach Activities
Cover crops, beneficial insects, interaction between pest and beneficial insects