PRE- and POST-applied herbicide options for alfalfa interseeded with corn silage

Abstract

Establishment of alfalfa by interseeding into corn planted for silage can enhance crop productivity but weed management is a challenge to adoption. Although a glyphosate-based herbicide program could be a simple and effective approach, concerns about herbicide resistance and limitations in available alfalfa varieties exist. Field experiments were conducted to compare the efficacy and selectivity of preemergence (PRE), postemergence (POST) and PRE followed by POST herbicide programs to a glyphosate only strategy when interseeding alfalfa into corn. Experiment 1 compared PRE applications of acetochlor, mesotrione, S-metalochlor, metribuzin, and flumetsulam, and found both rates of acetochlor and metribuzin, and S-metalochlor at 1.1 kg ha-1 were the most effective and selective PRE herbicides 4 weeks after treatment (WAT), but each resulted in greater overall weed cover than glyphosate by 8 WAT. Experiment 2 evaluated POST applications at early and late timings of bentazon, bromoxynil, 2,4-DB, and mesotrione. Several POST herbicides exhibited similar effectiveness and selectivity as glyphosate including early applications of bromoxynil (0.14 kg ha-1) and 2,4-DB (0.84 or 1.68 kg ha-1), as well as late applications of bromoxynil (0.42 kg ha-1), 2,4-DB (0.84 kg ha-1) and mesotrione (0.05 or 0.11 kg ha-1). A third experiment compared applications of acetochlor PRE, bromoxynil POST, and the combination of acetochlor PRE with bromoxynil POST. All treatments were effective and safe for use in this interseeded system, although interseeded alfalfa provided 65-70% weed suppression in corn planted for silage without any herbicide. Herbicide treatments had no observable impacts on corn and alfalfa yields so weed management was likely of limited economic importance. However, weed competitiveness can vary based on several different factors including weed species, density, and site-specific factors, and so further investigations under different environments and conditions are needed.

Ecological Intensification of Food Production by Integrating Forages

“…Successful establishment of forage legumes in a maize-silage companion crop for subsequent forage production appears to be highly dependent on management practices, growth environment, and the developmental characteristics and yield potential of maize. Multi-year studies in Wisconsin, USA demonstrated that alfalfa establishment in maize silage is favored by early interseeding prior to the V2 stage of maize using normal alfalfa seeding rates, and by planting maize at moderate maize populations to lessen competition and allow some penetration of direct sunlight to alfalfa seedlings following maize canopy closure [132][133][134][135]. Establishment of interseeded alfalfa in Wisconsin was further enhanced by planting a suitable variety [136] and by treating seedlings with the gibberellin inhibitor prohexadione followed by fungicide and insecticide to promote root growth and overall plant health [132][133][134]136].…”

“…Multi-year studies in Wisconsin, USA demonstrated that alfalfa establishment in maize silage is favored by early interseeding prior to the V2 stage of maize using normal alfalfa seeding rates, and by planting maize at moderate maize populations to lessen competition and allow some penetration of direct sunlight to alfalfa seedlings following maize canopy closure [132][133][134][135]. Establishment of interseeded alfalfa in Wisconsin was further enhanced by planting a suitable variety [136] and by treating seedlings with the gibberellin inhibitor prohexadione followed by fungicide and insecticide to promote root growth and overall plant health [132][133][134]136]. A similar study conducted in North Dakota had similar results to those of Grabber [132] but application of prohexadione did not improve alfalfa survival [137].…”

“…Interseeded alfalfa also suppresses weeds in maize [139]. When successfully established, first year dry matter yields of interseeded alfalfa are approximately two-fold greater than conventionally spring-seeded alfalfa but gains in alfalfa forage production are often partially offset by reductions in the yield of the maize companion crop [132][133][134]137,138]. Nonetheless, recent economic analysis found that alfalfa-maize silage rotations utilizing forage interseeding should increase annualized net returns by 7 to 33% relative to rotations using conventional spring establishment of alfalfa [164].…”

Establishment and First Year Yield of Interseeded Alfalfa as Influenced by Corn Plant Density and Treatment with Prohexadione, Fungicide and Insecticide

“…In this system, alfalfa is interseeded to serve as a highly effective cover crop for corn, and then it is brought into full forage production the following year. The successful interseeding of alfalfa reduces the risk of soil and nutrient loss from cropland, suppresses weeds, and increases the overall forage yields and profitability of corn silage-alfalfa rotations [8][9][10][11][12][13][14][15]. Full realization of these benefits will, however, require the reliable establishment of alfalfa while maintaining relatively high yields of the corn companion crop [10].…”

Stem Density, Productivity, and Weed Community Dynamics in Corn-Alfalfa Intercropping

“…Previous results are inconsistent regarding the impact of weed control on alfalfa forage yield [32], but more consistently indicate reductions in nutritive value from weed pressure. Weed control programs were also found not to impact total biomass accumulation in a corn silage and alfalfa system [52].…”