Reviewing this topic again after five years. I have about 20 plum trees now in my orchard, many of them large mature trees at this point. Control of black knot has remained one of the big challenges for plum growing here. Chemical control for black knot is best achieved with early spring sprays - first white to shuck split, and I like to use just one antifungal in my early sprays, and this has for a number of years been myclobutanil. The problem is that myclobutanil has no activity against black knot. I prefer to avoid chlorothalonil, mancozeb and captan for toxicity reasons, though each has activity against black knot. An alternative is propiconazole, which I usually reserve for rot later in the season in case resistance has formed to the myclobutanil, but instead plan to substitute for the myclobutanil in my early sprays as my primary antifungal and so address the black knot issue chemically while remaining with just one antifungal in my early regimen.

Chlorothalonil is the one always most highly rated- most fungicides don't work at all, but even CTL doesn't seem to help much and isn't supposed to. I actually spray the cuts with it when I remove the galls. If I wait until trees are dormant the disease gets away from me in highly infected orchards, but probably no harm in waiting at this point of the season. I will assume the best strategy is to remove the spore producing galls from the orchard as soon as possible until I see some actual research telling me otherwise. Why would you wait when galls are spreading innocculum to other trees? It's not like cutting them will increase the spread- it should decrease it. Also, during the growing season the galls also grow, sometimes girdling entire branches.

I was wondering if anyone has tried a Beneficial Nematode for RKN. Says its effective against RKN, I'm sure there must be others Here is a link that might be useful: Beneficial Nematode

Jo, I don't think they could have traveled from your soil to the styrofoam cups unless you flooded a bed with irrigation water AND the water ran over to the cookie sheet AND the water found its way up into the cups AND so on and so forth. So, please stop blaming yourself and relax, OK? I agree with PHJ and Dodie that it is likely she already had nematodes in her soil too. Root knot nematodes are incredibly common in southern parts of the country that have soil with a high sand content. In parts of Florida the RKN's are so bad that you have to raise tomatoes in containers elevated well above the ground so that the RKNs cannot travel via rainwater up throught the pots' drainage holes. Most photos I've seen from Florida posted by people who are fighting nematodes show their pots raised at least a foot above the ground and sitting on stone or cinder block walls, decks, etc. Y'all know, too, that the nematode-resistant varieties of toms can sometimes outlast the RKNs, right? So that explains why you'll often see them hit some plants but not all plants. Some plants resist or tolerate them well and others don't. Dodie, you're a real sweetheart and Jo's so lucky to have you for a friend! Dawn