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ARS Home » Pacific West Area » Logan, Utah » Pollinating Insect-Biology, Management, Systematics Research » Research » Research Project #441198

Research Project: Using Pesticide Fate Models to Guide Application Timing and Improve Alfalfa Seed Yields

Location: Pollinating Insect-Biology, Management, Systematics Research

Project Number: 2080-21000-019-041-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Oct 1, 2021
End Date: Jun 30, 2024

Alfalfa (Medicago sativa) has the third greatest production value of any crop in the United States, and over 16,000 acres were harvested in 2020. Annual seed production of alfalfa, though no longer specifically reported by National Agricultural Statistics Service (NASS), is estimated to be around 80 million pounds, with production almost exclusively in the western states. Production of alfalfa seed relies on bee pollination to produce marketable yields, with most growers purchasing alfalfa leaf-cutting bees (Megachile rotundata, ALCB), and some in CA and AZ renting honey bees. In Washington state, growers in the Touchet area have also been managing alkali bees (Nomia melanderi) for over 50 years in bee beds adjacent to the seed fields. Alfalfa seed growers also must manage pest populations that can lead to yield loss. Major pests include lygus bugs (Lygus hesperus) and spider mites (Tetranychus spp.). Lygus bugs in particular can cause significant damage to the reproductive organs of alfalfa flowers, resulting in reduced seed yield. Chemical control of these pests is currently the industry standard, and three knowledge limitations restrict our ability to improve insecticide application protocols, i.e. to make them more effective against pest insects and/or less harmful to bees. Critical lack of knowledge exists around (a) insecticide loss rates from fields after application, (b) insecticide concentrations in plants that result in toxicity effects on pests and bees, and (c) pest insect activity patterns by time of day.

Objective 1: Measure insecticide loss rates. Three timed treatments for four focal insecticides will be conducted. Testing will occur at the research alfalfa farm owned by the USDA, ARS Pollinating Insects Research Unit (PIRU) in Logan, Utah. A planting of alfalfa will be split into 24 blocks. Lambda-cyhalothrin will be applied to six randomly selected blocks, but at three different times with two replicates in each timed application. Rates will follow the label recommendations. Clippings of alfalfa leaves will be collected regularly (10 sample times) from the sprayed plots over the five days following application. Clippings will be random throughout the plot and equate to 5g of material per sample. The same methods will be repeated for an application of flonicamid during peak bloom, and applications of sulfoxaflor and naled during late bloom. In these trials, alfalfa flowers will also be collected from one plot for comparison to concentrations in leaves. Clippings from a control plot (no-spray) will always be collected at the same time as those from treatment plots to control for the effects of drift. Weather conditions will be recorded at each application and sample collection. Plant clippings will be stored in the dark at -20°C, and then residues will be quantified via gas or liquid chromatography with mass spectrometric detection in the Cooperators lab.