Passing this information on from Valent representative Jim Wargo. Keep in mind, the successful use of PGRs to offset frost damage is dependent on many factors, but ultimately hinges on sending a hormonal signal to receptive ovaries at the base of flower blossoms. Therefore application would be made later when trees are in early bloom. This gives time to assess any damage that may occur in the cold snap expected to come this Monday, April 20. =-TB
Managing Early-Season Frost Damage with Promalin® PGR
Freezing or near freezing temperatures are predicted for many parts of the northeast and mid Atlantic overnight on Monday April 20th. Depending on your location, apples may be in tight cluster or full bloom at that time. While apples are more cold-tolerant at the tight cluster to early pink stages than when fully open, temperatures of 27°F–28°F can still cause significant reproductive injury. Promalin Plant Growth Regulator can effectively rescue fruit set after such events, provided it is applied according to the tree’s natural phenology rather than immediately following the frost if trees are not yet in bloom.
Assessing Damage and Timing
Before treating, it is essential to determine if the injury threshold necessitates a rescue application. Remember, typically only one fruit per spur is needed for a full crop.
Some injury can act as a natural thinning event. Avoid overreacting to minor damage.
- Physical Inspection: Dissect flowers (opened or unopened) to inspect the reproductive parts. Brown discoloration indicates a dead pistil (the female organ), which prevents natural pollination and fertilization
- Limitation: If the vegetative receptacle tissue at the base of the flower is damaged or frozen, Promalin will be ineffective
- Patience is Key: Do not spray during the tight cluster or early pink stages. If trees are at full pink, wait until the first few king flowers open
The Science of Hormone Replacement
Promalin functions similarly to "hormone replacement therapy".
- Natural Process: Normally, fertilized ovules develop into seeds that produce cytokinins and gibberellins. These signals tell the tree to nourish the fruit and it will then develop normally.
- The Problem: If fertilization fails due to frost damage or poor pollination conditions (low bee activity) then no signals are sent, and the tree typically sheds the sterile flowers.
- The Solution: Promalin provides these missing hormonal signals to sterile flowers. This allows the fruit to develop to a normal size, though it will have a low seed count or be entirely seedless.