Project Number: 8042-22000-167-25-S
Project Type: Non-Assistance Cooperative Agreement
Start Date: Aug 25, 2019
End Date: Aug 24, 2024
Objective 1. Evaluate the potential for integrated weed management systems (harvest weed seed control, herbicides, and cover crops) to manage multiple herbicide resistant weed populations. Sub-objective 1.2. Quantify the potential for weed seed capture at harvest time across core and satellite locations at regional spatial scales. This will include the collection of empirical data on weed seed retention timing, and synthesis with a hierarchical mixed effects modeling approach that takes into account local environmental variation. Statistical models will be validated with on-farm data. Sub-objective 1.3. Quantify the efficacy of various harvest weed seed control technologies in weed and crop residue mixtures within cropping systems sampled at core and satellite locations. Sub-objective 1.4. Quantify the impact of multi-tactic integrated weed management that includes harvest weed seed control on the population dynamics and resistance allele frequencies of herbicide-resistant weed populations. Within corn-soybean crop rotations, we will create weed management treatments of varying complexity that consist of factorial combinations of harvest weed seed control, herbicide programs, and integration of cover crops.
Field experiments will be initiated in spring of 2020. This experiment will focus on characterizing the temporal pattern of weed seed production and dispersal in select crops (including: corn, soybean, wheat, and grain sorghum) for gravity dispersed weed species with a history of herbicide resistance. Seed rain will be monitored using 950 mL plastic containers. Traps will be mounted on wire stilts to exclude invertebrates and prevent seed-soil contact. A wire mesh cover will exclude vertebrates, and rainfall is allowed to drain through 0.5 cm holes in the bottom protected by 2 mm wire mesh. Traps will be placed in the crop fields prior to weed seed dispersal, and emptied weekly upon installment. Seeds will be compiled by species-crop combination, identified in the laboratory, separated and counted. Data from our empirical studies, as well as published and unpublished existing data sets on weed seed retention, will be combined to construct climate-based models that define regional agronomic and economic efficacy of harvest weed seed control. In addition, we will initiate testing, calibration, and necessary modification to the harvest weed seed control equipment (Sub-objective 1.3). Multi-tactic weed control tactics will depend on site, equipment and funding during the duration of the project. To complete Sub-objective 1.4, both a long-term experiment (core sites) and small strip-trials (satellite sites) will be initiated. Replicated strip-trials will be conducted testing a subset of the treatments being tested in the long-term experiment at the core sites. In the fall prior to soybean harvest, pre-harvest weed seed dispersal will be monitored by placing four aluminum pans, 30 cm in diameter, in the field with the onset of anthesis for target weeds, emptied and counted weekly. At harvest, the seed/chaff mixture that flows out of the back-end of the combine or combine + Harrington Seed Destructor will be collected using the same method for monitoring dispersal, sorted, and then target weed seeds counted. Seed viability will be determined using similar methods described above. The following spring, population density of the soil weed seedbank will be measured. Soil samples will be combined into a single composite sample per experimental unit. Composite soil samples will then be elutriated and then sieved, sorted, and tested for viability as above. After corn planting and just prior to postemergence herbicide applications, ~2-3 weeks after corn planting, emerged weed populations of target species will be recorded in nine evenly-spaced 0.125 m2 quadrats. Weed populations will then be recorded two weeks following postemergence herbicide application using the method described above. Crop yield and population will be recorded. Seedling counts will be used to assess seedling recruitment in relation to soil seedbank population density, as well as to determine efficacy of the herbicide treatment. Finally, corn yield and population counts of residual weeds will be taken at crop maturity.