Incorporating Native Plants in Insectary Strips to Promote Insect Diversity and Belowground Beneficial Microbes

View the project final report

Commodities

• Vegetables: onions, peppers

Practices

• Pest Management: biological control, integrated pest management
• Production Systems: agroecosystems
• Soil Management: soil quality/health

Insectary strips, a habitat management strategy, that increases the functional agrobiodiversity of agroecosystems has been associated with reductions in the number of many herbivorous pests, in temperate, subtropical, and tropical cropping systems (Gurr et al., 2003; Swift and Anderson, 1994). Increasing the functional diversity of agroecosystems by combining crops with non-crop, secondary plant functional groups that provide resources for natural enemies and/or alter the behavior and distribution of pests has been a particularly effective approach to pest management (Wilby and Thomas, 2002) and gained interest among farmers. Hedge rows or insectary strips generally grown for other purposes can also serve as hotspots for soil organisms with the selection of proper species.

Goal of this project is to maintain permanent insectary strips or field margins which not only provide pest management service but also serve as wind breaks and refuge for soil organisms during the summer period where the field interiors are generally bare fallow. We propose diversifying the field margins with south Texas native plants to maintain and promote soil health along with insect pest management. With the increasing cost of managing insect pests, small scale organic growers in this region have shown an interest in maintaining insectary strips with native plant species which require minimum resources for maintenance, and played a important role in development of insectary strip pilot study in the Fall and Spring of  2019. The preliminary results have indicated the pest management benefits of insectary strips but the soil health benefits remains largely unexplored, which informed the experimental design of this proposed research along with the farmers willingness to add diverse groups of native plant species.

Experimental Design

We will establish a randomized block experimental design to test the multiple benefits of insectary strips at a certified organic vegetable farm, Terra Preta Farm, in Edinburg, Texas. During the fall planting season of 2020, 3 feet wide insectary strips will be created in between every 8 rows and these three treatments will be replicated 5 times in a 3-acre plot at the Terra Preta Farm, where the farmers grows a mix of onions and peppers. These strips will be maintained during the summer bare fallow period and again in the fall of 2021.

We will incorporate, native legumes and plant that highly mycorrhizal in the insectary strips and analyze the soil microbes: bacteria, fungi, nematodes, and mycorrhizal fungi communities along with the abundance and distribution of insect pests and natural enemies of the cash crop. This study will include three treatment composition insectary strips:

• a cocktail of native plants including bundleflower, blue bonnet, and purple prairie clover Fabaceae); hooded windmill grass, pink pappusgrass, and shortspike windmill grass (Poaceae); Mexican hat, awnless bush sunflower, and orange zemenia (Asteraceae)
• nonnative hedge row species commonly used, sunn hemp (Fabaceae)
• control, no management

Data collection: Insects

Sticky traps, and pitfall traps will be installed in each of the treatment plots and will be collected biweekly. Insects collected from these traps will be grouped as herbivores, predators, parasitoids, and pollinators and analyzed to determine the insect diversity and beneficial pest ratio in the insectary strips compared to the control.

Cash crops

5 cash crops plants from each row be selected randomly to determine the proximity to the insectary strip and pest damage.  These plants will be evaluated biweekly when the plants start producing true leaves for insect damage and will be rated as high, medium and low pest damage. Total yield and marketable yield of the cash crops will also be monitored for each treatment.

Soil health

Rhizosphere soil samples and root samples of cash crops as well as hedgerow plants will be collected to analyze the microbial soil community and mycorrhizal colonization in the roots.

Roots and rhizosphere soil samples will be extracted from both the cash crop and hedgerows 2 times every season (early growing season and round harvest) to determine the nematode community and the prevalence of plant parasitic nematodes. We will also determine the total mycorrhizal fungi spore community assemblage and degree of mycorrhizal colonization in the roots of both cash crops and hedgerow plants.

The soil microbial community will also be analyzed following the FPLA extraction 2 times every season at the Soil Scientist in the Water Management Research Unit by Dr. Lauren Hale. Soil respiration will be measured biweekly with a 6400-09 Soil CO2 Flux Chamber during the study period.