Hello all, I have a recurring issue with the rootstock on JM grafts: The initial symptom is that the green bark turns black all around the trunk. Usually near the soil but not always. Initially the rest of the trunk is green. Very quickly the plant dies. It happens on rootstock I have grown from seed and on rootstock I have purchased. It happens mostly in the late summer although with the attached picture the one year old graft (Shaina) was just beginning to leaf out. So far it has only happened on high grafts and not on any low grafts or ungrafted seedlings I am growing. Less than 5% of the grafts are affected. In one case the rootstock tissue was only affected on about 180% of the trunk and the other side lived and is supporting the plant. The plant recovered, overwintered, and is pushing healthy buds as we speak (cross your fingers) and the damaged area is callousing around the edges. My thoughts: Perhaps the rootstock is stressed combined with the fact that the grafted variety has limited leaf area and it is not returning enough energy back to the plant to support the trunk tissue on the high graft. Possibly this is caused by keeping the potting soil too wet and the symptom is a result of root rot/damage? I'm a novice grafter (3 years) and having a great time doing it but I have much to learn. BTW I'm in Atlanta Georgia in case it matters for the diagnosis. In the picture the white mark in the affected area is where I scratched it with my fingernail.
This happens to me as well. Do not know the cause. Would love to know, so let's hope we get more responses to this thread.
Google 'root rot'. I think i get this in my seedling beds if i plant too close and/or if i water too much.
As mentioned above, there are several fungi (or water molds) that can do that. Phytophthora is a fairly common cause of root rot in the southeast. Fusarium is also a plausible cause. Verticillium is also possible, but what you are showing doesn't look like that to me. They typically thrive in wet conditions. Excellent draining soil is a must for young trees especially, coupled with lower moisture during winter months. Protection from extreme cold is also a good idea when they are that small. And finally I would consider a soil drench with something like Captan, Subdue, or Alliette in the fall and late winter.
Wet feet is something I struggle with when I pot them up. I'm moving towards a better draining soil mix. Seems that most of the homegrown rootstock where I mixed bark/sand/perlite fared the best and produced strong grafted plants.
