I have an organic heirloom yellow taxi tomato that has developed yellowing on the leaves, with brown spots in the parts that are yellowed. The leaves also seem to be curled down and are contained to the bottom half of the plant, although the plant is in general much smaller and weaker than the rest of the tomatoes in the garden. The early girl tomato plant right next to it also looks like it is in the beginning stages of developing the same thing.
They are planted in partial sun (a bit less than half day), which is not ideal but the other tomato pants are thriving for the conditions. I live in Ottawa and we have been getting a high volume of rain this season so they have had consistently moist soil (a mix of top soil and plant and animal composts) which has somewhat worried me.
Could this be from too much water or is it caused by something else? Also, is it possible to help the plant, and are the fruit at risk or will they be ok? Up to this point, it seems to have developed fruit well (about ten on the plant, and a few more tiny ones emerging).
Thank you for your help!
Growing tomatoes in one’s garden provides wonderful rewards. However, tomatoes can be susceptible to many foliar diseases; although heirloom tomatoes may have better flavour, they unfortunately lack disease resistance to many diseases. Your description and photo of the afflicted tomato foliage indicates possible septoria leaf spot. The septoria leaf spot is fungal which could have developed due to decreased air circulation and too much water. The fact that an adjacent plant is developing the condition, yet the others are thriving, supports this diagnosis. The fact that the heirloom variety was the only plant to initially showing signs of foliar disease also indicates its susceptibility to such problems.
Septoria leaf spot usually appears on the lower leaves after the first fruit sets. Spots are circular, about one-sixteenth to one-fourth inch in diameter with dark brown margins and tan to gray centers with small black fruiting structures. Characteristically, there are many spots per leaf; they do not look target-like. This disease spreads upwards from oldest to youngest growth. If leaf lesions are numerous, the leaves turn slightly yellow, then brown, and then wither. Fruit infection is rare. Lookalikes: bacterial leaf spot and speck (no tan centers); and other diseases that progress from the bottom up. See: https://bit.ly/1GyT1PZ
Here are some suggestions on how to minimize the effects of this problem: the fruit should not be affected.
You may arrive at a different conclusion after reading through the above references; there are quite a number of tomato diseases. Fortunately, most can be prevented or minimized with an awareness of the cultural requirements for growing healthy tomatoes. Hopefully, you will be able to enjoy a plentiful crop of tomatoes this summer.
Thanks for getting in touch with the Toronto Master Gardeners.