Underseeding Organic Wheat with Clover: Impacts on Fusarium Spp. Inoculum Dispersal, Deoxynivalenol Concentration, Crude Protein, Grain Yield, and Weed Biomass.

Underseeding clover in wheat production is a practice utilized by numerous organic wheat producers in the Northeast.  Little is known about how clover underseeding affects Fusarium head blight (FHB) of wheat (Triticum aestivum L.) and associated concentrations of the mycotoxin, deoxynivalenol (DON), a limiting factor for organic wheat production in the Northeast.  This study conducted in 2010 and 2011 examined FHB and DON levels and assessed other grain quality variables in organic spring wheat (‘AC Superb’) underseeded with either medium red clover (Trifolium pratense L.) at 14 kg/ha, medium red clover at 28 kg/ha, Ladino white clover (Trifolium repens L.) at 14 kg/ha, or Ladino white clover at 28 kg/ha in three Vermont locations with fields containing grain crop residue from the previous season.  The hypothesis was that FHB, DON, and CFUs would be highest in control plots due to greater soil and crop residue exposure, and that clover treatments may produce higher grain yields and crude protein due to possible transfer of N to wheat roots. The effect of clover understory on FHB and DON levels was checked by quantifying Fusarium spp. inoculum collected from vertical rain-splash collectors placed in experimental plots at heights of 30 and 100 cm.  Rain-splash samples were plated onto modified Nash-Snyder agar media to compare colony forming units (CFUs).  Statistically significant differences (p<0.05) in treatment means of FHB incidence, Fusarium spp. CFUs, DON concentration, crude protein, and yield were only observed at one location in 2010, though significant reductions (p<0.05) in weed biomass between treatments was observed at multiple locations in 2010 in clover treatments compared to no clover.  Such findings may indicate that clover underseeding does not negatively impact FHB incidence, DON concentration, grain yield, or crude protein and is successful in reducing weeds biomass in Northeast organic wheat systems.