Don’t worry about streptomycin resistant Erwinia amylovora; there are numerous options. Here are some key things to remember.
SmR Ea is not a regional problem (there’s no cloud of SmR Ea), it’s a local orchard level problem. The most prevalent strain is 41:23:38 and is passed in trees and budwood.
Also, every farm (except for a few non-commercial farms) has a mix of sensitive and resistant strains. This provides an opportunity for competition and elimination of resistant strains.
If you don’t have SmR Ea on the farm:
If you don’t have a confirmed detection of streptomycin resistance on your farm, you can protect yourself from future outbreaks.
Get trees from established nurseries and be careful with on farm nurseries.
During bloom always rotate antibiotics: Options include using a mixture of 1) Streptomycin and Oxytetracycline at the full rate each. 2) Alternate with Kasugamycin, but target on cloud days or evenings. 3) Alternate with Oxytetracycline (not if you used it in a mix), coppers (if safe) and biologicals as needed.
Epiphytic populations seem to spike at night. Try to make evening applications instead of morning applications. This also helps avoid breakdown of products by solar energy (use a sunscreen adjuvant).
If you have SmR Ea on the farm:
Conventional: At both ‘Pink’ and ‘Petal Fall’. Apply of prohexadione-calcium (Kudos, Apogee, etc.) of 2 oz/100 gal mixed with 1oz /100 acibenzolar S-methyl (Actigard).
During Bloom: Apply kasugamycin (Kasumin 2L) at 64 fl oz/A in 100 gallons, Blossom Protect (1.25 lbs/A + 8.75 Buffer Protect; OMRI listed – I’ve not had russet problems but use something else at PF) or oxytextracycline at the highest rate. It’s entirely possible to have an effective program consisting of only of Blossom Protect. This is the best option for organic production systems, but numerous other soft products can be effective. BP has consistently performed as well as antibiotics in all university trials in CA, WA, OR, MI, and NY. Not sure where PA stands on this one. It’s not about what works well in my trials, it is something that has worked well all trials.
Shoot elongation. Continue with prohexadione-calcium to slow systemic infections and Low MCE liquid coppers to limit spread of shoot blight.