Heat or drought stress during critical stages of bud differentiation can result in the formation of double pistils in many stone fruits. If these flowers are pollinated, the resulting malformed “double” or “twin” fruit are not marketable. The frequency of double fruit in Utah tart cherry orchards has increased in recent years. To determine the critical time of flower bud formation for doubling, whole-tree treatments of induced heat stress were imposed for one-week intervals from July to September in 2022 and 2023. The resulting doubling incidence was observed in the following spring and at harvest. There were seasonal differences in the frequency of doubled fruit between years, but the highest incidence of doubling in both years resulted from induced heat stress at 4 to 6 weeks after harvest. Understanding this timing is important in targeting alleviation strategies such as evaporative cooling or spray-on orchard protectants.
