1a.Objectives (from AD-416):
1. Evaluate early- and mid-season growth regulator treatments for promoting the establishment of interseeded glyphosate-tolerant alfalfa without limiting yields of glyphosate tolerant corn.
1b.Approach (from AD-416):
Objective 1: With assistance from the ARS SY, the University of Wisconsin will handle planting of glyphosate-tolerant corn at two locations in May along with fertilizer applications, pest control, and harvesting of whole-plant corn for yield in September at roughly 35% dry matter. The ARS SY will interseed glyphosate-tolerant alfalfa into corn during May and, with assistance from the University of Wisconsin, will handle pest control and measurement of alfalfa forage yields under a 3-cut harvest management during the following year. In initial studies, the University of Wisconsin will spray prohexadione-Ca in June and, with the ARS SY, assess affects on alfalfa growth during corn production and 4–6 weeks following corn harvest. Subsequent studies will examine the use of prohexadione-Ca with other foliar or seed applied growth regulators to identify promising approaches for modulating competition between the co-seeded crops and for enhancing the establishment and subsequent production of interseeded alfalfa. The ARS SY and the University of Wisconsin will jointly plan experiments, analyze data, and publish results.
The project originally had two objectives, but due to the phase out of imidazolinone-tolerant corn by the seed industry, studies examining forage legume interseedings into imidazolinone tolerant corn (formerly objective. 1)were not pursued. Efforts are now focused on studies with glyphosate tolerant alfalfa interseeded into glyphosate tolerant corn (formerly objective 2). In mid-May 2012, corn and alfalfa were planted at normal versus reduced seeding rates at two sites in Wisconsin. One site was subsequently abandoned because unusually dry spring conditions caused highly variable establishment of alfalfa. At the second site, the gibberellin-inhibitor prohexadione-calcium was sprayed at several rates via drop nozzles on alfalfa herbage in split applications at 38 and 48 days after planting or in a single application 48 days after planting. The later application was made just before canopy closure of corn. We also included non-prohexadione treated control plots seeded only to corn and control plots seeded with corn plus alfalfa. Alfalfa growth will be evaluated about 70 days after planting and about 35 days after corn harvest to assess the effectiveness of prohexadione treatments for controlling stem elongation and promoting plant survival. Silage corn yields will be determined in mid-September and yields of interseeded alfalfa will be evaluated the following year under a 3-cut harvest management. After the final harvest, alfalfa stand density will be determined by counting undercut plants. Yields and stand counts of interseeded alfalfa treatments will be compared to spring-seeded alfalfa planted into plots sown the previous year to corn. Because this field study was just planted in May 2012, there are no further results to report at this time.