In nine replicated, small plot trials in ID and WA conducted during 2009, effects of a mycorrhizal stimulant (formononetin) and a Systemic Acquired Resistance inducer (HRPN_αβ – ‘harpin’) alone or in combination were evaluated in Irish potato.  Treatments included three rates of formononetin (Myconate® ST) applied to seed pieces at planting, two foliar timing regimes of harpin (Employ®), and a combination of one formononetin rate with one timing regime of harpin.  Compared with the untreated control, treatments had no effect on stand, stem number, vigor and plant height; however, treatments increased root weight from 6% to 15%, increased tuber set from 10% to 28%, and increased gross yield by 2% to 8%.  Highest gross yields were achieved with the combination entry, but highest marketable yields were achieved with 3 foliar applications of harpin.  Yield increases were attributed primarily to increased set.  Marketable yields were improved more than gross yields, demonstrating an increase in quality and improved crop value.