Foliage mowing in June-bearing strawberry ( <i>Fragaria</i> × <i>ananassa</i> ) ‘Polka’ after harvest has variable effects on floral development in the northern climate

Abstract In many parts of the world, strawberry ( Fragaria × ananassa ) plants are commonly defoliated after fruiting to promote photosynthesis in the remaining leaves and to enhance floral initiation and further development of flower initials. We studied the effect of foliage mowing conducted at different times after harvest on ‘Polka’ strawberry floral development and yield in two consecutive years. Field trials were carried out on two strawberry farms in Southern Ostrobothnia, Finland, between 62°58′ N and 62°69′ N. The foliage mowing treatments were applied at different times between 20 July and 13 August. The effects on the crown carbohydrate reserves, flowering and yield were recorded. Flower mapping analysis was used to evaluate the treatment effects on floral development in the fall. The effects of foliage mowing at different times on ‘Polka’ strawberry generative development were relatively small but consistent. The SPAD value of the leaves increased on one farm through early mowing, but crown carbohydrate reserves were not increased by removing old foliage. The earliest mowing reduced crown branching and increased the number of flowers in the inflorescence. The late mowing interfered with floral development, as it decreased the number of inflorescence initials and either delayed floral induction or retarded floral development after induction, as observed through flower mapping analysis. Mowing also decreased the number of flowers and fruits per plant on one farm, which led to a non-significant trend towards larger fruit. In conclusion, mowing off old foliage as soon as possible after harvest can be recommended, but late mowing should be avoided, as it interferes with floral induction or floral development during the fall. Significance of the study What is already known on this subject? Defoliating strawberry ( Fragaria × ananassa ) after fruiting may enhance flower initiation and further development of floral initials by promoting photosynthesis in the remaining leaves and results in higher fruit yield. However, the challenge at the northern latitudes is the relatively narrow time window for carrying out this practice between the termination of harvest and the time of floral initiation. What are the new findings? The earliest mowing at the end of July reduced crown branching and increased the number of flowers in the inflorescence. Mowing may also decrease the number of flowers and fruit per plant and thereby increase fruit size. The late mowing interfered with floral development, as it decreased the number of inflorescence initials and either delayed floral induction or retarded floral development after induction, as observed through flower mapping analysis. What are the expected impacts on horticulture? In the northern climate, mowing off old strawberry foliage as soon as possible after harvest can be recommended, while late mowing should be avoided, as it interferes with floral induction or floral development during the fall.