The 2011 ASHS Annual Conference

A number of improvements are still needed in the performance of strawberry row covers before they can be viewed as a stand alone technology for strawberry frost and freeze protection, especially during the blossom period. Several of the problems with row covers for frost control in this important crop stage relate to: 1) unreliable blossom protection levels on nights of frost or freeze when prior-day weather conditions are cloudy and cold; 2) poorer pollination and fruit set when the crop must stay covered for several consecutive days and nights because of frost concerns; 3) mechanical damage to the crop from row cover 'flapping' against the crop on spring days and nights of very high winds; and 4) it may not be feasible for the operator to  find enough hand labor to keep applying and removing covers on a daily basis during a spring of multiple frost episodes like the spring of 2011 in North Carolina. On one of the radiation frost nights in the Sandhills of North Carolina (March 29), growers who were fully dependent row covers experienced much higher blossom losses than producers using sprinkler irrigation. On this occasion, the daytime conditions prior to the frost event were overcast and cold (~10 °C), and this prevented any significant build-up of heat beneath the covers during the day.  That night,  air temperatures beneath the covers dropped slightly below 0 °C, and with dew point temperatures in the range of –1.1 °C to 0 °C, a damaging frost occurred underneath the cover. Growers using sprinkler irrigation, or who used irrigation as a back-up for row covers during this high dew point radiation event, had nearly perfect protection. However, blossom losses approached 15% for growers who relied on row covers alone. The mechanization of row cover application and removal represents an important solution to a number of the current problems associated with row covers, but there also needs to be wider recognition given to the continuing importance of  sprinkler irrigation in a fully integrated strawberry frost and freeze management program.