Establishment of alfalfa intercropped under corn in response to varying rates of prohexadione with or without fungicide plus insecticide

Authors: Grabber, John; DIAS, JOSE LUIZ - University Of Arizona; RENZ, MARK - University Of Wisconsin

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2023
Publication Date: 11/15/2023
Citation: Grabber, J.H., Dias, J.C., Renz, M.J. 2023. Establishment of alfalfa intercropped under corn in response to varying rates of prohexadione with or without fungicide plus insecticide. Agronomy. https://doi.org/10.3390/agronomy13112823.
DOI: https://doi.org/10.3390/agronomy13112823

Interpretive Summary: Establishing alfalfa by interseeding it into corn grown for silage has the potential to suppress weed growth, reduce soil erosion and nutrient loss from cropland, and increase overall forage yields and profitability of crop rotations. The purpose of this study was to determine suitable rates of a growth retardant (prohexadione, PHD) to apply prior to a fungicide-insecticide treatment (FI) for promoting good survival of alfalfa seedlings growing under corn. We found FI alone was sufficient to promote excellent seedling survival under normal growing conditions but both PHD and FI should be applied to ensure fair to good seedling survival under highly stressful wet growing conditions. Our results will help farmers to apply appropriate rates of PHD and FI to ensure good establishment and subsequent forage production of interseeded alfalfa.

Technical Abstract: The establishment of interseeded alfalfa under corn silage is often enhanced by foliar applications of prohexadione (PHD) growth retardant followed by fungicide plus insecticide (FI) but rates of application must be optimized. We evaluated stand characteristics of alfalfa interseeded two years at Arlington, Wisconsin USA in response to PHD applied in mid June at 0 to 0.423 kg a.e. per hectare followed two weeks later with FI (none vs. 0.147 kg a.i. per hectare fluxapyroxad-pyraclostrobin at plus 0.018 kg a.i. per hectare lambda-cyhalothrin). PHD reduced etiolation while FI treatment increased plant health and vigor of alfalfa. Following corn harvest, stands of nontreated alfalfa averaged only 4.2 plants per square meter and 1.2% groundcover under wet growing conditions in 2019 compared to 71.3 plants per square meter and 15.9% groundcover under normal growing conditions in 2020. By contrast, stand density in 2019 reached 130 plants per square meter but failed to plateau with combined PHD-FI treatments while in 2020 stand density averaged 177 plants per square meter with FI treatment regardless of PHD rate. Alfalfa groundcover plateaued at 63% in 2019 and 71% in 2020 when PHD at up to 0.30 kg a.e. per hectare was applied prior to FI. The results of this study indicate FI promotes excellent establishment of interseeded alfalfa under normal conditions but both PHD and FI should be applied to ensure fair to good establishment of interseeded alfalfa under wet conditions.