Establishment of Alfalfa Intercropped under Corn in Response to Varying Rates of Prohexadione with or without Fungicide Plus Insecticide

Abstract

Establishment of interseeded alfalfa (Medicago sativa L.) under corn (Zea mays L.) silage is enhanced with foliar applications of prohexadione (PHD) followed by fungicide plus insecticide (FI), but the lowest effective rates must be determined. We evaluated stand characteristics of alfalfa interseeded into corn at Arlington, Wisconsin, USA in response to PHD applied at 0 to 0.423 kg a.e. ha−1 followed two weeks later with FI (none vs. 0.147 kg a.i. ha−1 fluxapyroxad-pyraclostrobin plus 0.018 kg a.i. ha−1 lambda-cyhalothrin). Application of PHD reduced etiolation, while FI treatment increased plant health and vigor. Following corn harvest, non-treated alfalfa stands averaged 4.2 plants m−2 and 1.2% groundcover under wet growing conditions in 2019 compared with 71.3 plants m−2 and 15.9% groundcover under normal growing conditions in 2020. Stand density in 2019 reached 130 plants m−2 but failed to plateau with combined PHD-FI treatments, while in 2020, stand density averaged 177 plants m−2 with FI regardless of the PHD rate. Alfalfa groundcover plateaued at 63% in 2019 and 71% in 2020 when 0.16 to 0.30 kg a.e. PHD ha−1 was applied prior to FI. The results indicate that FI enables excellent alfalfa establishment under normal conditions, but both PHD and FI should be applied during wet growing conditions.

Intercropping in maize silage versus solo‐seeding for alfalfa establishment in Wisconsin and Idaho

“…The timing of interseeding after maize planting and the application of PHD had little or no effect on alfalfa stand density in either state (Figure 4). Application of PHD often improves plant survival of interseeded alfalfa in Wisconsin (Grabber, Smith et al., 2021; Osterholz et al., 2018), but other studies carried out under normal to dry growing conditions in the Eastern and Midwestern United States also found that stand density of alfalfa intercropped with maize was in some cases lower than spring‐seeded alfalfa or not responsive to PHD treatment (Berti, Lukaschewsky et al., 2021; Berti, Cecchin et al., 2021; Grabber, Osterholz et al., 2021; Grabber, Dias, & Renz,2023; Patel et al., 2021).…”

“…ha −1 of fungicide (fluxapyroxad and pyraclostrobin) and 0.018 kg a.i. ha −1 of insecticide (lambda‐cyhalothrin) were also applied during establishment to spring‐seeded and interseeded alfalfa in late June or early July to suppress foliar disease and insect pests and to enhance seedling vigor and survival (Grabber, Smith et al., 2021; Grabber, Dias, & Renz, 2023).…”

“…The growth-retardant PHD-calcium was sprayed at 0 or 0.28 kg a.i. ha −1 onto interseeded alfalfa seedlings in mid-June (Grabber, Dias, & Renz, 2023). In Wisconsin, 0.147 kg a.i.…”

“…2. Identical to system 1 but with prohexadione (PHD) growth retardant sprayed onto alfalfa to enhance seedling survival (Grabber, Smith et al, 2021;Grabber, Dias, & Renz, 2023). 3.…”