Phraggy, please correct me if I'm wrong; but, I assume that's an Imperial gallon (4.55 litres), not a US gallon (3.8 litres). Thanks.
Troy and Mrhappyrotter; Erwinia is a bacterial infection, not fungal. Advising anyone to use a fungicide is of no help whatsoever as a treatment for bacterial infection. If you want to kill a bacterial infection, you must use a bactericide (which is topical), like Physan, H2O2, or even alcohol. Or, use an antibiotic which is systemic; but, I'm not aware of any systemic antibiotics for plants (while there are numerous systemic fungicides; but, as I said, they don't kill bacterial infections). That's why when our plants have a bacterial infection like Erwinia, the first action is to surgically remove the infected tissue completely.....because the treatment cannot get inside the tissue to treat it from the inside - out. Then, spray the plant with a topical bactericide to help prevent re-infection at the wound site. Also, you must attend to changing the environmental conditions that allowed/encouraged the infection to thrive in the first place. That means possibly increasing the light and/or increading the air movement and/or admitting more fresh air and/or lowering the humidity and/or adjusting the feeding schedule, or the nutrient ratio. Also, if the temps are too warm, lower them. If they're too cool, raise them. All of these environmental conditions affect the stress load on a plant. The more elements that are out of whack with what the plant wants, the more stressed the plant becomes and the more susceptable the plant is to invasion by all infection agents/pathogens. The Erwinia bacteria is EVERYWHERE. There is no point in wondering why a plant in one location and another 10 feet away got an infection. The pathogen is all over all the plants inbetween, as well. What gives rise to the infection is the genetic tendency of the plant to be susceptable, the general health/stress level of the plant and the environmental conditions, which can help or hinder the plant....as well as they can help or hinder the infection pathogens.
Attending to all these things and closely monitoring how we care for our plants is what makes us "Slipper growers" instead of "Slipper consumers". But, at the VERY least, learn the difference between a fungicide and a bactericide and choose the CORRECT treatment, if you actually want good results.
I also advise to then spray the entire plant with Aspirin water (one 325 mg tablet disolved in 1 litre of water). The ASA does not kill any pathogens. However, it does boost the plant's response to the infection and it helps the plant fight off the infection itself. In combination with increased air movement, I have found this to be the best way to halt Erwinia and save the most plants.