Recipient Organization
NORTH CAROLINA STATE UNIV
(N/A)
RALEIGH,NC 27695
Performing Department
Entomology and Plant Pathology
Non Technical Summary
Most of the corn and cotton grown in the US, expresses Bt toxins designed to kill major insect pests. The US categorizes Bt toxins as "public goods" at risk of being lost due to resistance. Corn growers are required to plant 20% of their total corn acres to non-Bt (refuge) corn to delay the evolution of Bt resistance. However, very few growers plant non-Bt corn, primarily because insecticide susceptibility is a common pool resource. Prior research from our group has shown that major seed companies have high-yielding non-Bt hybrids available. Our proposal will demonstrate the yield potential of these non-Bt hybrids paired with closely related Bt hybrids. We will do this on 45 farms and in 13 Official Variety Testing for each of two years across North Carolina and Virginia. We will also train Cooperative Extension agents on general corn agronomy and how to identify insect damage so that they can collect data. This data will feed into a damage abatement model to estimate the short run-impacts of non-Bt hybrids, as well as a long-run economic analysis to account for the difference in the evolution of resistance when planting non-Bt hybrids. Finally, this information will be distributed to stakeholders through publication on the North Carolina Cooperative Extension corn portal, presentations in county winter meetings, and through incorporation into the Variety Selection Tool database. Growers use this tool to select hybrids appropriate for their farm based on data gathered from NC Official Variety trials planted in multiple locations across North Carolina.
Animal Health Component
(N/A)
Research Effort Categories
Basic
(N/A)
Applied
(N/A)
Developmental
(N/A)
Goals / Objectives
Our overall objective is to demonstrate how non-Bt corn refuges can be used to slow the pace of resistance without profit loss for growers. Specifically:1. To train Cooperative Extension agents to assess insect pest damage in corn2. To demonstrate the performance of non-Bt (refuge) and Bt hybrid pairs directly with agents, growers, and seed industry representatives under a range of pest pressure3. To evaluate the short-run and long-run economic impacts of planting non-Bt corn hybrids (in lieu of Bt hybrids) as refuge in farm operations4. To disseminate the results of this model to relevant stakeholders
Project Methods
Objective 1: Regional Cooperative Extension agent trainings will be held in both North Carolina (n=4) and Virginia (n=4) during both 2022 and 2023. The purpose of the trainings will be to standardize data collection including stand count, species identification at R3 and R5, percent kernel consumption at R5 on the tip and cob, and yield (see methods in next objective for details). The trainings will be held at a location where the corn is in the R3 growth stage. Ears at R5 and with feeding will be brought from a different field to train agents on how to quantify the extent of larval ear feeding.Objective 2: Bt and non-Bt hybrid pairs appropriate for North Carolina have been identified from representatives of two of the three major commercial corn seed breeders: DeKalb (DKC65-93 RR2, DKC65-99 Tre; Bayer Crop Science) and Pioneer (P1197R, P1197YHR; Corteva). While there are other smaller seed companies, they derive their Bt germplasm from these three main companies.We will plant these hybrids in Cooperative Extension agent-led demonstrations in at least 30 locations across North Carolina and in at least 15 locations in Virginia. Location will be the replicate and each location will contain a single plot of each hybrid. All corn plots will be >four rows wide and > 40 m long and the pairs will be planted within 50m of one another. Larger plots will be planted when possible to minimize cross-pollination by other hybrids. Plots will be planted using commercial corn planters at various populations depending on soil type and fertility. Planting will be attempted in the recommended agronomic planting windows. Plots will be maintained using agronomic recommendations from their respective Cooperative Extension Services.Stand counts of 10m-row will be made prior to layby from three random locations in each plot to confirm that stands between the hybrids pairs are equivalent. The first insect damage assessment will take place at R3. If leaf damage is present, agents will rate 20 consecutive plants per plot at a randomly selected spot.The second insect damage assessment will take place at R5. Usually most larval pests have finished feeding by this time, although in rare situations, larvae will feed on more mature kernels. In these cases, a damage assessment will be made once the larvae finished feeding. One hundred random ears will be sampled in each plot and the area of unpollinated kernels (tip) and pollinated kernels (cob) consumed will be quantified. Fifty consecutive plants per plot at a randomly selected spot will be examined for entrance holes and frass around the leaf axil or shank of the ear, as evidence of stalk tunneling from European corn borer.In addition to the Cooperative Extension agent-led demonstrations, the hybrid pairs will be planted in the Official Variety Testing (OVT) trials in North Carolina across nine locations, each, during 2022 and 2023 and at four Virginia Tech Agricultural Research and Extension Centers. At each location up to 100 varieties are evaluated, being a mixture of Bt and non-Bt hybrids. The hybrid pairs will be planted in all four replicates of the randomized complete block design with each plot containing four rows planted 6.10m long. The pairs will be completely randomized. Planting will begin in late March and will finish by early May. Plots will be maintained by the OVT program using agronomic recommendations provided by NC State University and the NC Cooperative Extension Service. At physiological maturity, corn yield, moisture, and test weight will be collected per plot. All assessments described previously for the agent-led demonstrations will also be collected from the OVT trials.Objective 3: Economic evaluation of non-Bt corn hybrids is critical to determine whether these hybrids could be viably utilized by farmers as refuge plantings. Demonstrating that planting these non-Bt hybrids can generate short-run and long-run net economic benefits (i.e., benefits greater than costs) is a key factor to encourage growers to plant non-Bt corn as refuge in the Southeast.The economic assessment component of this project is envisioned to be a four-step process. First, relevant yield and input use data from the "paired" field demonstration plots will be collected. We will specifically take note of input applications and management practices that differ across plots within a site, and those that differ across sites. This will allow for controlling potential covariates that may influence the observed yields in each plot-site combination. Information on soil and other environmental conditions in each demonstration site will be collected as well.Second, short-run partial budgets will then be developed where changes in annual profitability (per acre) will be assessed by determining the profit-increasing and profit-decreasing changes that results from using non-Bt hybrids as refuge (as compared to the counterfactual scenario of simply using Bt hybrids and not complying with refuge requirements). Data from the paired Bt and non-Bt plots will be utilized to statistically determine whether yields and input use for non-Bt are different (or the same) as Bt. For example, if annual input costs for non-Bt is lower than Bt, then this will be part of the cost-decreasing component (and profit increasing) in the partial budget. Mean difference tests (e.g., t-tests) and regression approaches (more on this below) will be used to determine statistical differences in yields and/or inputs. Data on pertinent cash crop prices and input prices (e.g., wages, seed prices, technology fees, etc.) will also be collected to attach values to the changes in yields, inputs, and other non-pecuniary factors from planting non-Bt corn refuge. Partial budgets for low and high pest pressure scenarios will be developed and sensitivity analysis will be conducted as well.Third, the yield and other data from the field trials will also be utilized to estimate traditional (e.g., Cobb-Douglas) and damage abatement production function models to further assess the short-run yield impacts of using non-Bt hybrids. These production function estimations would allow us to more precisely estimate the mean yield impacts of planting non-Bt hybrids, conditional on control covariates (e.g., pest pressure, inputs, weather, and soil). In particular, the traditional and/or damage abatement models would allow us to examine the mean yield (and yield variance (or risk)) effects of planting non-Bt hybrids, accounting for the damage control nature of Bt/non-Bt plants.Lastly, long-run economic analysis will be conducted to better account for the difference in the evolution of resistance when planting non-Bt hybrids over a specified planning horizon (e.g., 10 or 20 years). Long-run partial budgets, traditional net present value (NPV) approaches, and simulation models will be developed to assess long-run benefits and costs of planting non-Bt hybrids as refuge. Parameters from the production function models in the third step, and previously published examples of dynamic bioeconomic models of Bt resistance evolution, will be used to develop the long-run simulation models under both high and pest pressure scenarios. Sensitivity analysis will be conducted using alternative parameter values and assumptions to assess robustness of simulation results.Objective 4: Results will be published on the North Carolina Cooperative Extension corn portal and presented in winter county extension meetings. Results will also be incorporated into the NC State Variety Selection tool as decribed in the "products" section.