What’s Affecting My Tomato Plants?

This is the time of year when your tomato plants may start showing signs of disease.  Here’s a summary of what might be affecting your plants.

Septoria Leaf Spot:  In the picture above, the tomato leaves are yellowing and have brown spots on them.  The leaves eventually become totally brown and shrivel up.  There is no cure once it appears.  Tomatoes planted in the same garden spot each year are especially susceptible to leaf spot.  Wet conditions, high humidity, and crowding of plants that limits air flow contribute to the infection.

Blossom End Rot:  Tomatoes ripen, but an ugly black patch appears on the bottom and it is soft and mushy.  This is a sign of a lack of calcium or the pH is too low for the plant to absorb any available calcium.

Late Blight:  Caused by a fungus which develop greasy-looking irregular shaped gray spots on tops and undersides of leaves.  A pale ring develops around the spots which eventually turn dry and papery.  Copper sprays offer some control but it isn’t a cure.  Remove all infected foliage, put it in a plastic bag and dispose of it in the trash or burn.


The best ways to prevent diseases from taking hold is to pay attention to soil, spacing, watering and drainage.  Plant tomatoes in a new spot each year.  Planting in raised beds that have not shown signs of disease helps and allows for excellent drainage.  Do a soil test to determine pH.  Tomatoes like a pH of around 6.5.  Give plants plenty of room, up to 24 inches all around.  Remove the bottom 6-8 inches of leaves to prevent spores from being splashed or blown onto leaves from the soil.  Prune out excess foliage from interior of plant to allow for air flow. Mulch heavily with straw or hay. Never put diseased plants in the compost pile.

Reference:  https://www.thespruce.com/tomato-leaf-diseases-1403409