Yellow Polka Dotted... Tomatoes??

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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.


tomato leaf mold, high tunnel tomatoes
Tomato leaf mold symptoms on upper leaf surface


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.


Tomato leaf mold, high tunnel tomato production
Yellow polka dots on high tunnel tomatoes from Tomato leaf mold fungus


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!


tomato leaf mold spores
Underside of tomato leaf showing lesions of Tomato leaf mold with characteristic spores


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.


tomato leaf mold lesion underside of leaf
Close up of tomato leaf mold lesions on underside of leaf


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.


tomato leaf mold on high tunnel tomato
Tomato leaf mold lesions on high tunnel tomato leaf


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!