Fire blight & streptomycin questions

By Terence Bradshaw

I’ve received a few questions about the fire blight alert:

  1. If you are in an inland/upland site and no bloom or fresh pruning wounds, this alert does not apply. However, I bet most apples in the state, aside from some late cider varieties, will be in bloom before this disease alert is done.
  2. Strep can be applied within 24 hours before or after an infection / wetting event. So you could wait to see if there is dew, but need to know that there’s no dew if you decide to hold off. Dr. David Rosenberger from Cornell has also been discussing the possibility that high humidity may be enough to cause infections. Bottom line- I’d get out there sometime if you have any risk (susceptible blooming varieties, past history).
  3. A treated flower is a treated flower. So if you’re at full bloom and you’re going to treat anyway, treat any time.
  4. Rate: I was corrected on the rate of streptomycin that I’d recommended, which I’d passed on from another extension warning without reading the label. Harbour is the main (only?) brand of strep we use in the state, and it is labeled for 24-48 ounces per acre. The first application should include Regulaid or similar wetting agent, subsequent sprays, if applied, can and should omit the wetting agent to reduce phytotoxicity.
    The Harbour label is a bit confusing, as it makes some jumps from concentration to rate with an implied understanding of (and I’d say controversial application of) tree row volume. We’ll discuss TRV another time, not during an important disease event. Stick to the label rate, which is 24-48 ounces per acre.

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