Yesterday, I went to look at a friend’s tomato plants, which were doing poorly. A quick inspection showed that, whatever the plants were suffering from, it wasn’t one of the fungal “wilt” diseases, and it wasn’t Early Blight (I recognize those on sight), so we wrapped a leaf in a damp paper towel for me to bring home for research.
I used Cornell’s Vegetable MD Online pages for tomato diseases to figure out the problem, which seems to be Bacterial Speck. The black dots were small, numerous, and ringed with yellow. In addition, one characteristic of this disease is that it thrives in cool, wet weather, which is exactly what we had for most of the early part of this year’s growing season, in April, May, and the first week of June.
It’s hot now, but my friend’s plants are in bad shape. One plant has lost nearly all of its leaves, some plants have several leaves that are completely wilted, and all the plants have spots on all of their leaves.
The several websites that I eventually read agree that the most common way a garden becomes infected with this disease is through infected seeds or transplants. I started from seed most of the tomato plants that my friend is growing, but my garden is not infected, which means that the disease is unlikely to have come from the Cherokee Purple, Arkansas Traveler, Rutgers, Yellow Marble, or Amish tomatoes that I gave her.
I did grow one variety for her that I did not keep any plants of for myself; it was the variety Black Seaman. She also brought in at least one other tomato plant from another source. Either one of these could have been the source of infection (and I plan to burn that packet of Black Seaman seeds, just in case…), but for now, the biggest question is whether any of her plants will survive.
The remedy mentioned on most websites I visited was spraying with a copper-based fungicide: either a Bordeaux mixture or a copper-maneb spray. However, research from western North Carolina suggests that some strains of the bacteria that causes speck (Pseudomonas syringae pv. tomato) have developed resistance to copper sprays. I am hoping that the strain in my friend’s garden is not among them.
Ways to limit the spread of this disease were mentioned in several online sources:
1. practicing clean cultivation (removing and disposing of plant debris–continually)
2. keeping tomato leaves dry
3. using mulch to avoid spread by splashing in heavy rains
4. choosing disease-free seeds and transplants (though this, obviously, is tough)
5. making sure plants are far enough apart that they get good air circulation and that one infected plant has a lessened chance of infecting all the others through splashing