Wow! You have done your research! Red leaf, also called bacterial soft rot, is caused by a bacteria called Erwinia rhapontici. As you have found, there doesn’t seem to be too much available on controls. It appears that there are several host plants, so you may want to be sure not to grow those in the same area that was infected by the diseased rhubarb. How far away you need to plant healthy plants might depend on the vector; if it is by flying insects, then 20 feet may not be enough. Strains do not seem to be host-specific, meaning that they can attack more than one type of plant. Amaranthus hybridus (a weed) seems to be a host, and the bacteria was found on roman chamomile, peppermint, and lemon balm; there are several others. One vector is thought to possibly be insects—so controlling them may help prevent the spread to other areas/plants. Some sites specifically mention controlling eelworms. One source suggested removing infected soil, but that might not be practical. Be sure to maintain good sanitation, and remove plant debris and weeds around the area; the pathogen can overwinter on infected plant tissue. A few sources mention that using Bacillus subtilis looks promising; I don’t know if this is available in a product registered for use on rhubarb in Canada, but here is some information:
The following scientific article from 2003 provides some information on the disease that might be useful (it contains a list of host plants):
Wow! You have done your research! Red leaf, also called bacterial soft rot, is caused by a bacteria called Erwinia rhapontici. As you have found, there doesn’t seem to be too much available on controls. It appears that there are several host plants, so you may want to be sure not to grow those in the same area that was infected by the diseased rhubarb. How far away you need to plant healthy plants might depend on the vector; if it is by flying insects, then 20 feet may not be enough. Strains do not seem to be host-specific, meaning that they can attack more than one type of plant. Amaranthus hybridus (a weed) seems to be a host, and the bacteria was found on roman chamomile, peppermint, and lemon balm; there are several others. One vector is thought to possibly be insects—so controlling them may help prevent the spread to other areas/plants. Some sites specifically mention controlling eelworms. One source suggested removing infected soil, but that might not be practical. Be sure to maintain good sanitation, and remove plant debris and weeds around the area; the pathogen can overwinter on infected plant tissue. A few sources mention that using Bacillus subtilis looks promising; I don’t know if this is available in a product registered for use on rhubarb in Canada, but here is some information:
The following scientific article from 2003 provides some information on the disease that might be useful (it contains a list of host plants):
Hope this helps!