Subfreezing temperatures as low as 30 oF is expected midnight tonight (Friday) to 10:00 am Saturday for northwest and western Virginia. Our cherries, peaches, and most, if not all, apple varieties are at the post-bloom stage now. The critical temperatures that can cause 10% and 90% of damage at this stage are 28 oF and 25 oF, respectively. At this stage of apple crop development, frost can cause damage to the fruits and seeds. Fruits with damaged and aborted seeds stop growing and eventually drop off. Therefore, it’s important to assess your crop first for any frost injury before starting thinning applications this coming week. You can do so by picking a few fruitless from different locations in the orchard and cut them in half by a pocket knife and observe the flesh and seed color. Damaged fruitlets will show brownish flesh and seed color. In most cases, the damage can also be observed on the fruit surface as a frost ring (See images below).
The model predicts apple freeze damage potential for the Red Delicious apples in Winchester, VA, at petal fall. However, the date presented in the chart are also suitable for other apple varieties. The yellow horizontal line indicates that temperature at which 50% of fruits can be killed. The blue color refers to the mini temp forecasted, which is 31 oF for Saturday, May 9.
Sherif M. Sherif, Assistant Professor at Virginia Tech, School of Plant and Environmental Sciences, AHS Jr. Agricultural Research and Extension Center
595 Laurel Grove Road, Winchester, VA 22602
540-232-6035, Email: ssherif@vt.edu