High spring temperatures decrease peach fruit size

The growth and productivity of peach fruit can be limited by many factors, including weather. Previous research indicated that early-spring temperatures for 30 days after bloom have a strong effect on early peach fruit growth, and both the time and potential fruit size at harvest. We analyzed fruit-size trends of three major cultivars in the California fresh-market peach industry (Flavorcrest, Elegant Lady and O’Henry) over a 20-year period to determine if there is a clear relationship between early-spring temperatures and packed fruit sizes industrywide. This research confirmed two significant trends: the size of packed fruit has increased over the 20-year period between 1985 and 2004, and high early-spring temperatures tended to decrease the size of packed fruit at harvest for any given year. Over the past few decades, models of peach fruit growth and plant development have identified useful principles for assisting growers in making horticultural management de-cisions. For example, harvest-date pre-diction models are now available to aid in managing fruit crops (Ben Mimoun and DeJong 1999). The unusually early harvest of California’s peach crop in 2004 — which had record high temper-atures during bloom time — and atten-dant difficulties in attaining the fruit sizes desired by the market (DeJong 2005) have increased interest in using physiological concepts to understand the effects of early-spring temperature on peach fruit growth and in anticipat-ing fruit size at harvest. The dependence of peach fruit devel-opment on spring temperatures during the first 30 days after bloom has been established; there is a strong correlation between the sum of growing degree-hours accumulated in the 30 days after bloom (GDH30) and the number of days between bloom and harvest for several stone-fruit cultivars (Ben Mimoun an