Apple Growers Need To Be Cautious About Frost Treatment

Apple Growers Need To Be Cautious About Frost Treatment

Editor’s Note: We recently posted a story about using Promalin, a Valent USA product, to help apple growers get a crop when it would ordinarily be lost to frost. According to Cornell Cooperative Extension Specialist Mario Miranda Sazo, one of the Editorial Advisory Board members to American Fruit Grower® and Western Fruit Grower® magazines, as well as a frequent contributor, there is some confusion among growers on the use of the product. Below we have posted Sazo’s April 6 “Horticultural and Pest Management Notes.” We ran the following by Valent’s Greg Clarke, who said he agreed with Sazo, and that pre-bloom applications would be off-label. The upshot: Always, always, follow the instructions on the label.


By Mario Miranda Sazo and Matt Wells, with additional comments provided by Poliana Francescatto and Dan Donahue, Cornell’s Lake Ontario Fruit Program

Low temperatures in Western NY: On Tuesday morning (April 5) several weather stations registered temperatures in the low 10s. Freezing temperatures lasted for at least 6 to 8 hours. Matt crunched the hourly temperature data for eight weather stations and found that orchards located in the west side of Rochester escaped the bitter cold, or were less affected, than orchards located in Wayne County. (See graph.)

GP Sazo Temp Chart

The southern-most sites in Wayne County saw very low temperatures for a longer period of time. As expected, inland orchards experienced the lowest temperatures. Fairville and Lafayette weather stations registered 9.5˚F and 1˚F, respectively. Sodus registered 3˚F. In Peru temperatures dipped to around 11˚F to 12˚F.

Can you use Promalin at this moment? Today I had the opportunity to visit orchards, assess the damage, and talk with growers about frost protection methods, Promalin use, and pruning. I got the idea that there is still a confusion with the use of Promalin and its effectiveness if applied at this early stage of bud development.

Promalin won’t be effective if applied in the next two-three days at the green tip stage, 1/4 inch stage, or 1/2 inch stage. It won’t help a damaged bud to continue its development the following week. Promalin can only improve fruit set when flowers (not buds) are damaged but not totally killed by a frost.

In 2012 we tested the use of Promalin after a frost (28˚F) at late bloom and had a significant improvement in yield. The Promalin did not completely restore a damaged crop to a full crop but did provide a significant benefit. In our trial the application of Promalin improved fruit set more than enough to pay for the spray and in some cases by 10 times the cost of the product (recommended rate: 2 parts Promalin per acre using 100 gallons of water per acre within 24 hours of the frost event). Promalin is most useful with a hard frost (lower than 29°F) when there is significant flower damage. If the frost event was marginal (30˚F to 32°F) and caused damage to only a small portion of the flowers then the Promalin spray is not likely to be needed since there will still be many more flowers still alive than are needed for a full crop.

Please remember that you only need 8%, 9%, or 10% of all flowers to set a good crop.

Additional Comments About Promalin – By Poliana Francescatto

The work done by Steve McArtney in 2012 that proved Promalin would work as a frost-rescue treatment for apple was done at bloom, between pink stage to petal fall. There is no study done at earlier stage that would support the effect of Promalin on fruit set.

We are experiencing much lower temperatures than what researchers had in 2012 at bloom when they tested Promalin as a frost-rescue treatment. I think the critical differences between 2012 and 2016 are two-fold: 1) the stage of the crop when the frost hit (full bloom in2012 vs green tip or tight cluster in 2016, and 2) the temperatures (high 20s in 2012 vs low 20s in 2016).

I would not encourage any grower to put Promalin on at this stage. I know growers go desperate trying out everything but I believe they would waste money at this point.

Promalin to Remediate Frost Protection? – Dan Donahue

Promalin PGR has a supplemental label (2EE) in New York for frost damage remediation in apples. The label is for application during the bloom period, within 24 hours after the frost event. The gibberellins in Promalin mimic those that would have been produced by the non-existent seeds in the damaged fruitlets. As a result, the seedless fruit remain on the tree. Would Promalin work if applied now, at this early timing? From what I have learned from email contacts today, the consensus is no, Promalin will not work at this early timing. Not to mention that its use at this timing would be off-label. However, Promalin may become a valuable tool during bloom if the frost risk persists.