ASHS 2025 Conference

Blackberry (Rubus spp.) growers in the Pacific Northwest (PNW) regularly experience freeze damage, which limits yields and on-farm revenues. Freeze mitigation using wind machines, in-field heaters, and overhead sprinkler irrigation is costly and may not be economical. Sprayable biostimulants, in contrast, are potentially more affordable and readily adaptable as they can be applied using equipment readily available on most farms. However, the efficacy of biostimulants at mitigating freeze damage is largely unknown. The objective of this study was to evaluate the effect of a glycine betaine-based biostimulant on the freezing damage of ‘Victoria’ floral buds. The biostimulant (FRUIT ARMORTM) was applied four days before a freezing event at its highest label rate (4.5 kg/ha) to three consecutive rows in different areas of a commercial farm in Skagit County, Washington. The foliar application was compared to an untreated control. Floricanes from both treatments were collected two days after a second frost and scored for damage by quantifying the presence or absence of damage to primary floral buds from a total of 720 treated and 720 untreated buds. A mixed-effect logistic regression model was used to analyze the data and account for cane and location variability, as well as estimate the expected probability of damage to the floral buds. The foliar application of glycine betaine increased freezing tolerance and reduced the expected probability of damage in the buds by 5.5%. Furthermore, the odds of bud damage in the control were 1.42 higher compared to treated buds. Results indicate that glycine betaine promotes freeze tolerance and may be a cost-effective strategy for blackberry growers to reduce freeze damage. Further research should be done to evaluate other biostimulant active ingredients as well as the optimal timing of biostimulant application and cost-benefits relative to other freeze mitigation practices.