It’s that time of the year once again when we start getting nervous about bud break and spring frost, and with the crazy weather pattern and swings in temperatures we have experienced in the last few weeks I thought this could be a timely resource for growers.

Studies in New York and North Carolina State have reported that applications of the plant growth regulator Promalin (gibberellin plus cytokinin) following a severe frost event can significantly increase fruit set and yield in apple trees by mitigating frost damage of flowers. Promalin will stimulate the retention of fruit with unviable seeds that otherwise would have dropped. Basically, it sends signals to fruitlets that the seeds inside are still viable and that it should keep on growing. This often results in the development of parthenocarpic (seedless) fruit.

The recommended rate of application is 1 pint (16 oz) of Promalin per acre using 100-150 gallons of water per acre within 24-48 hours of the frost event. However, there is evidence that applications up to 3 days after the frost event can still increase fruit set. The product can be applied from pink to petal fall stages; if applied later once fruit size is between 5-20 mm it will provide very little benefit. Ideally the product should be applied once temperatures rise to 65°F. However, if temperatures do not
warm up the product can still be applied with cooler temperatures, as long as it is during the 3-day window of application.

Applications of Promalin work best after a significant frost event (below 28°F), when there is extensive flower damage. If the frost is not that severe (29-31°F) the application of Promalin may not be necessary, because probably there will be more flowers alive to achieve a full crop. Growers should assess the level of damage to their crop and determine the stage of development of flowers and fruitlets before applying the product. The studies conducted in NY and NC States were performed in Gingergold, Jonagold, and Gala on M.9, and Taylor Spur Rome on M.26, respectively.

There are still many questions to be answered regarding this “rescue treatment”, and it is certainly not way of setting a crop. Each grower will have to consider on his or her own if it is worth trying an application of Promalin to rescue the crop.

This article was posted in Apples, WFN, Vol. 1-4 and tagged Amaya Atucha, Apples, frost damage, Frost Protection, frost rescue, Promalin.