Dear Nancy:

Thank you for your question, which has been forwarded to the Colorado State University Lawn and Garden Help Desk. Given the wet weather we have had recently and the fact that your plants are growing in a greenhouse, it is possible that your tomatoes are showing early signs of tomato leaf mold. If this is the case, you would see older leaves affected first with pale greenish-yellow spots that do not have sharply defined margins. These spots are typically less than 1/4-inch diameter. On the underside of the affected leaves, you would see olive-green to brown velvety mold spots. Eventually, the leaf spots would grow together and turn brown, causing leaves to wither and die. Attached please find additional information (including treatment plans) related to tomato leaf mold.

Additional questions to think through in diagnosing these leaf spots: 1) do your plants have good air circulation and adequate spacing? 2) with what are you fertilizing your plants and how often? 3) how often and how much are you watering? 4) do you see any insects or signs of disease on the undersides of the plant leaves or around the plant bases? If you would like to bring a plant sample to our in-person Help Desk, we would be happy to take a look at it under the microscope. The Help Desk is open 9-12 and 1-4 p. m. (Mondays, Wednesdays, and Thursdays) and is located at 17 N. Spruce Street in Colorado Springs. You can also contact us directly at <personal data hidden> or <personal data hidden>. 

Happy gardening!

Heidi V. 

Colorado Master Gardener