I would question any table if I didn't know how they came up with their evaluations (well, it if contradicted my own experience, that is). Maybe it is a question of state, but in the sites I manage Methely is much more susceptible than any of the many plums growing- this includes over 20 different varieties, including Damson. In my nursery I have Methely growing with other varieties and over the years it is so hard to manage for black knot that I'm not going offer it anymore. You can see all the extra wounds in this variety from cutting, cutting , cutting. In home orchards there is usually some sun blockage and if this occurs from the east the equation will be much different than on any university testing site. I have 3 Damsons on a site with good exposure and it doesn't suffer more than other plums there. However, on that site Methely doesn't suffer a whole lot either although a bit more than the Damsons. But then, I've resisted Damson's tendency to be a dense upright growing tree- a form that makes drying difficult. You cannot know about how easy or hard black knot is to manage unless you have managed it at multiple sites. There is huge variability on the problem that often can't even be explained by sun exposure or nearby native cherries.

Chokecherries seem to be prone to black knot. Depending on your climate, it could be a problem to you. I've got chokecherries that grow among pie cherries and plums in a bit of a jungle. Many of the older chokecherries have some cankers, and on occasion it will show up on a cherry. I don't recall seeing the plums showing any signs. But--I am in a very dry climate where moisture to aid in the spread of the disease is fairly uncommon. Since it has never bothered me, I've never done anything about it--didn't even know what it was until fairly recently. So, depending on your climate and the specific susceptibility of your trees, you may or may not have a problem. Still, if it is present in your area, you may want to take preventive measures. Otherwise, you could risk an infection, remove it as soon as you find it, then start treatments going forwards. Kocide is used as a foliar spray as a bacterial disease preventive/inhibitor on some crops, though it may be used at a lighter rate than when you dormant spray. Kocide doesn't cure an infection, so you must apply it before the infection takes hold to inhibit the initial infection or slow its spread. This means it is usually applied earlier in the growing season or just before the time the tree is most susceptible to infection. Nude Gardener: Many of the names listed are the trade names you would purchase the product under. Often they are capitalized. The chemical names are usually not capitalized, and sometimes, though not always, sound more "chemical-like". Many of these chemicals are sold in the garden sections of your favorite local stores and the big box stores, plus at garden centers/nurseries. If in doubt, do an internet search on the term and you'll find out pretty quickly whether you have a trade name or a chemical name, and you can quickly get the other name. Also read the label to see what crops and uses it is registered for. Unlike medicines, if the use you have planned is not labeled, it is illegal to use it for that crop/purpose. The blue stuff is copper sulphate, which is the active ingredient in Kocide. The crystals are not as easy to dissolve in water, but they do work in drains to kill tree roots. Kocide is formulated so that you can easily get the proper concentration of copper sulphate in water and to ease application. Some of these products are not sold for the home market. Sometimes they present a greater safety risk, so they will not be sold to homeowners who are not expected to have any knowledge in proper use and safety with pesticides (I'm not saying home users don't use them properly, but nothing says a home user HAS to know how to use the product, so mis-use is more likely). Others will not be sold to the homeowner because the companies deem the market to be too small, or the EPA is trying to limit exposure potential to the general public. Commercial formulations will be packaged in larger quantities and concentrations for use by commercial growers. However, if the product is labeled for the crop you have and will use it on, it is perfectly legal to purchase it from a farm supply. The main drawback is that it will generally come in packages that will treat a number of acres, which means a 20 year supply for the home gardener. If you are purchasing a commercial grower's product, you may need a private applicator's license, depending on your state's laws. If you do, the cooperative extension service in many states handles the training and/or testing for these licenses, so you can check with them to get certification and a license. The private applicator's license where I am is pretty common. It takes about a half day of classroom instruction on the safe use of pesticides, calculating application rates, reading labels, etc.

Both 2 and 3 will not be helpful. Even the most affective synth fungicides have limited efficacy against this disease but chlorathalinal is said to be helpful although it's hard to tell in my experience. It certainly doesn't make a big difference. You needn't treat with alcohol between wounds if you cut to clean wood. Next year cut out knots as they occur. Keep plum growing with good vigor.

prune prune prune...make sure you get well below the black knot ...I had it on a plum tree (hybrid) about 5 years ago..i've yet to see anything come back.