Tomato stem disease
I've cross-posted this posting on Great Lakes Gardening Forum.
Every year for the past four years, I've had the same tomato disease in the spring. It attacks the stem of the young plants, right at the soil line. It eats through the stem, leaving a dry core exposed, going up about 1 inch from the soil. Sometimes there are thin streaks of dry exposed core running all the way up the stem.
It's not a cutworm because the plants are too big (over 40 cm) and it's a slow decay rather than being chewed through in one night.
Eventually, the affected area dries right through the stem, and the plant falls over.
There are no symptoms other than the dry corroded area at the soil line. There is no obvious fungus, no slime. The leaves are full and green until the point where the plant topples over. When I cut the stem, there is just healthy green flesh inside, no discoloration, no streaks of red or grey.
I've searched through hundreds of internet tomato sites, and I have never found anything that matches it. I would like to know what it is so that I can do something about it.
Three facts that suggest it might be fungal:
1. It seems to strike after a cold spell in the spring. So the cold spell we had over the past few days cost me half my tomato plants, even with greenhouse coverings.
2. It seems to affect the heritage tomatoes more than the hybrids.
3. Last year, I delayed planting a few of my heritage tomatoes till mid June, and they avoided this disease entirely. Any plants that don't get the disease in early spring don't get it at all.
Two facts that suggest it might be insect:
1. The stem looks as if it has been chewed in a one-inch circle girdling the stem. The streaks going up the plant may be the plant's reaction to the damage.
2. If one plant in a cage is affected, the other plants in the cage will be affected too (I put three plants in a cage, big cages). Then neighbouring cages will be affected.
I've had my soil tested. It's over 7 for pH.
If anyone has any ideas, or photos you could point me to, I would appreciate it. I dissected the plants after I pulled them this year, so I don't have any photos.