I was called out to visit a high tunnel vegetable grower, who was concerned about what he was seeing on tomato leaves, which he hadn’t seen before on the plants. He told me that spots had suddenly began to appear on his tomato plants, and that he really didn’t want to lose the plants or the huge crop of tomatoes that the plants had set.
I’m always on the lookout for a new disease or problems invading the vegetable producers in the county, so I went out to see what was going on with the tomatoes. Of course, this was after the rains and storm front from the tropical storm Cindy had kept things nice and damp for a couple of days. One thing that I have experienced over my years in Extension is that when these storm fronts from hurricanes and tropical storms blow up from the South, they often bring with them diseases and problems that we don’t typically see until the very end of our growing season.
Consequently, I was a little surprised as I walked into the high tunnel to see different sizes of yellow polka dots, scattered over the foliage of the tomatoes. In case you were wondering, yellow polka dotted tomato leaves are not a common sight!
Of course, the first thing to do is to turn the leaf over to see if the spot is only on one or both sides of the leaf. In this case, the characteristic cluster of olive-green to dark brown, velvety spores of the fungal pathogen Passalora fulva, previously called Fulvia fulva or Cladosporium fulvum, and commonly known as Tomato leaf mold, were easily seen.
Certain fungicides can be effective in managing this tomato disease in high tunnel production and interesting enough, this disease is rarely seen in field-grown tomatoes.
If left unchecked, these individual leaf spots begin to coalesce, causing the leaf to turn brown. Infected leaves will wither and die but often remain attached to the plant. If there are no leaves, then there are no photosynthates to size up the tomatoes and no shade to allow the fruits to ripen gradually. The fungus can also infect the new blossoms, causing them to turn black and fall off the pedicel. No leaves, no blossoms, leads to no red, ripe fruits. If this happens, then the best option remaining is—fried green tomatoes!