PRINCETON, Ky. — Kentucky experienced a prolonged advective freeze during the nights of March 12-16th wherein temperatures in the low teens and low 20’s were common across much of the state. In the months prior to this event, the state experienced above average warmth and 3-10 times greater accrual of growing degree days (GDD base 45°F) compared with the prior 10 years, resulting in a roughly 30 day advance of the normal season.
A large variation in floral development among fruit species and cultivars was observed on March 6 at the UKREC research orchard. The apple cultivar ‘Fuji’ generally exhibited the least growth, having a visual estimation of 20% dormant, 50% silver tip, 20% green tip, and 10% halfinch green buds, respectively. Peach cultivars had a wider range of development states. ‘Crimson Lady’ displayed more advanced maturity with a majority of flowers in the pink (50%) and bloom stages (30%), while ‘Redhaven’ was somewhat more delayed with a majority in the pink (50%) and half-inch green (30%) stages.
As the 20 and 17.5°F lows on March 16th and 17th (Kentucky Mesonet) in Princeton exceeded the 25°F LT(10%) but not the 15°F LT(90%) for peach flowers at the pink stage, it is possible that a substantial loss occurred. Similarly, apples in the half-inch green stage have an Lethal Temperature (LT) (10 and 90%) of 23 and 15°F, respectively. However, any loss of apple blooms is likely not as dramatic as for peaches considering their less advanced development state overall, leading to the expectation of normal yields for the 2017 harvest season, and barring any further damage
On March 16, flower bearing shoots were collected from ‘Redhaven’ and ‘Crimson Lady’, peach trees at the UKREC orchard, Princeton, KY. Flowers were categorized FRUIT HUMOR What Do You Get When Strawberries Cross the Road? Usually, a Traffic Jam! 7 as non-viable (dead) and viable (alive) along with the percentage of each. The average number of viable flowers per shoot inch and the projected percentage of full crop was then calculated (Table 4).
Significant differences were observed in floral viability between the cultivars ‘Redhaven’ and ‘Crimson Lady’. Thirty-six percent of the ‘Redhaven’ flowers were deemed viable while less than three percent of those from ‘Crimson Lady’survived. Despite the loss sustained by ‘Redhaven’, a crop greater than 2.5 times that of a full is still possible. Barring any additional fruit damage, this would require further thinning to prevent over-cropping. In contrast, ‘Crimson Lady’ with roughly 3% viability and 1/10 potential yield is expected to sustain a total crop loss for 2017.
Advanced floral development during the freeze episode inevitably contributed to the near complete mortality of ‘Crimson Lady’ while the more delayed growth of ‘Redhaven’ resulted in greater viability. ‘Redhaven’ is described as requiring 950 chill hours while ‘Crimson Lady’ is portrayed as needing 650 chill hours. Evidently, the greater chilling needed by ‘Redhaven’ in this situation served as a safeguard against crop loss. Cultivars with similarly high or higher requirements, trialed previously in Kentucky and suggested for commercial production include Contender (1,050), Coralstar (950), Cresthaven (850-950), Encore (850-950), Harrow Diamond (950), and White Lady (850-950).
— Daniel Becker, UK Extension Associate and Dwight Wolfe, UK Research Specialist, Kentucky Fruit Facts
For more news from Kentucky, click here.