With more than 20 million of trees planted in Washington State, ‘WA 38’ apple, commercialized as ‘Cosmic Crisp®’, is channeling the interest of the apple industry. Since the variety hit the market in 2019, consumers reported positive eating experiences and appreciation for its crispiness and juiciness. In suitable growing conditions, ‘WA 38’ can achieve high red coloration and satisfactory pack-out. One of the causes of loss is the ‘green spot’ (GS) disorder that impacts mainly the stem-hemisphere of the apple displaying skin discolored areas that might degenerate affecting the cortex. The onset of the GS occurs at the end of July, and the disorder incidence at harvest fluctuates year to year. Several mitigations approaches were investigated, but only bagging fruit at early stage of development provided positive results. Because the bagging practice is not economically sustainable on commercial scale, the application of a new foliar biostimulant (Plants for Plants 4-Vita) and Promalin (GA4 7 BA) were tested against untreated control. 4-Vita aims to protect the trees by abiotic stressors like drought and heat, stimulating water use efficiency and productivity. On the other hand, Promalin is known to improve fruit shape and size and reduce russeting by increasing epidermis cell elasticity. Our hypothesis focused on the potential positive effects of a biostimulant and a PGR in mitigating the GS in ‘WA 38’. The products were tested in season 2023 on a Granny Smith/M9-T337 orchard top-grafted in 2015 with ‘WA/38’ scions and trained to spindle, by applying them separately on distinct rows, bi-monthly, starting at 4 weeks AFB for 4 times. Productive parameters, pack out and GS incidence GS were assessed for each treatment. Results showed that Plants for Plants 4-Vita and Promalin did not improve yield and did not significantly mitigate the incidence of GS in comparison to untreated control.
