Important updates about freeze damage and fire blight

John Aue wants us to spread the word about the following:

1)      Applying foliar nutrient spray to frost- and freeze-damaged trees

Michigan Extension is reporting lots of stressed-looking fruit trees in their area. The trees have reddish leaves or leaves with red margins. Discussions coming out of Michigan and Cornell are suggesting that it would probably be a good idea for growers to apply a foliar nutrient spray to frost- and freeze-damaged trees to speed recovery.

One of the main goals of this strategy is to reduce tree stress. When stressed, not only is a tree less resilient in the face of damage like many of you witnessed over the past couple nights, but it also is more likely to drop fruit, whether or not the tree has suffered any damage.

John recommends that you follow the nutrient combination outlined in an article by Ed Stover of Cornell University. I’ll post the formulation here; find the link to the full paper at the bottom of the page.


Products were applied as follows: B at 22.8 mM (1.2 g of formulation per L) using the product Solubor (>99% disodium octaborate tetrahydrate; U.S. Borax, Valencia, Calif.); 0.75 mM Zn as Zn- EDTA (Clean Crop, 9% zinc EDTA; Platte Chemical Co., Fremont, Nebr.; 2.5 mL·L–1); and 59.4 mM urea (45% N, microprilled, agricultural feed grade; BP Chemicals, Lima, Ohio; 3.6 g of formulation per L).

WARNING!:  The particular products referenced in the above paragraph could be safely tank mixed with a current fungicide cover without any issues of toxicity or incompatibility. However, other formulations of zinc (such as zinc sulfate) might not be compatible and could cause phytotoxicity.

2)      Important reminder about fire blight

John wants to remind everyone that in most of your locations, Friday and Saturday nights will have lows in the 50s. If it rains those nights, we would have high potential for a fire blight outbreak by Sunday afternoon. Two warnings:

A)     If you are still pruning your trees, you should stop by tomorrow (Thursday, April 12) to make sure that the wounds will be able to heal before bacteria potentially infect them over the weekend.

B)      If you have fire blight concerns in certain varieties, you have two options with this weekend:

More recommended: Wait and see what happens, then apply streptomycin 24 hours after the infection period (apply on Sunday). The streptomycin will have the same efficacy against the fire blight as it would if it were applied 24 hours before the infection period. Sunday weather conditions present the only danger with this option: if rain, wind, etc. prevent you from spraying on Sunday, then you’ll have missed the optimal window.

Less recommended: Apply streptomycin on those varieties on Friday, before the bacterial growth period is reached.

Good luck! See the article on foliar nutrient sprays below.


Article: Stover, Ed et al. “Prebloom Foliar Boron, Zinc, and Urea Applications Enhance Cropping of Some ‘Empire’ and ‘McIntosh’ Apple Orchards in New York.” HortScience 34(2):210-214. 1999.

NOTE 1: This article is clearly not perfectly relevant to our present situation. The researchers focused on trees damaged by extreme fall and winter cold and on pre-bloom nutrient sprays. However, John thinks its nutrient formulation is sound.

NOTE 2: We were referred to this article through the Great Lakes Fruit Workers email list. To join their list, go to