Microclimates, peach bud phenology, and freeze risks in a topographically diverse orchard

Peach [Prunus persica (L.) Batsch.] production in the southeastern United States has suffered a decline in the past several decades due to late and severe spring freezes. Mulch of the peach production in Tennessee is located on topographically diverse sites. Peach producers do not have adequate information about the effects of microclimates within their orchards on peach bud development and subsequent freeze risk. Such information may help them select the best adapted cultivars based on microclimate. The objectives of this study were to use a 'Redhaven' peach bud development model to compare and contrast the phenology and freeze risks at five sites within the orchard, and to study the freeze characteristics (advective vs. radiative) of these same sites. Automated weather stations were located in topoclimatically different areas of a peach orchard in Dandridge, Tenn., from October 1990 to April 1992. Hourly weather data included average air temperature, drill units (CUs), growing degree hours (GDHs), and wind speed. The data show that the microclimatic factors that affect peach bud development and freeze risk, such as CUs, GDHs, and minimum temperatures, can vary in a topographically diverse orchard, but the effects are not as straightforward as previously reported. For instance, peach buds at a site at a lower elevation may break dormancy later due to slower accumulation of CUs, which could be beneficial to the grower. Then the buds may develop more slowly due to cold air drainage to the lower elevations, which would also be desirable. However, the lower temperatures due to cold air drainage could be damaging to the bud and cause more problems with injuries. Over the two seasons, there were more radiative freezes than advective freezes, but the advective freezes were more severe. Small differences in wind speed can account for surprisingly different freeze conditions during radiative situations. Any improvement in cold air drainage should help decrease the duration and severity of radiative freezes.