Metarhizium anisopliae seed treatment increases yield of field corn when applied for wireworm control

In an effort to protect field corn (Zea mays L.) from wireworm (Agriotes obscurus L.) herbivory and yield loss, seeds were treated with conidia of Metarbizium anisopliae strain F52 alone or in combination with clothianidin or spinosad before planting at three farm fields in south coastal British Columbia, Canada. Corn seed treated with M. anisopliae conidia (main effect) resulted in significant increases in stand density (78% M. anisopliae treated vs. 67% no M. anisopliae) and stock and foliage area fresh wt. yield (9.6 Mg ha(-1) M. anisopliae treated vs. 7.6 Mg ha(-1) no M. anisopliae), and significantly increased plant (stock and foliage) fresh wt. when it was applied together with spinosad or with no additional agrichemical at one location. Spinosad had no effect on corn yield, whereas clothianidin caused a significant increase in plant stand density and yield. Wireworm cadavers showing M. anisopliae strain F52 growth were retrieved from treated plots, suggesting that the increase in yield may have been due to wireworm control. Laboratory experiments provided no evidence that the increase in stand density and yield from the M. anisopliae-treated corn seed was attributable to an increase in germination rate or root growth. We concluded that seed treatment with this fungus may be a novel method to increase stand density and yield of corn.