Question:
I have spotty leaves and green tomatoes, not red ones . How can I do better next year?
Answer:
Despite being a favorite ‘vegetable,’ tomatoes have their problems. Recently, late blight was reported in the area of Rt. 79 east, and then at the Cornell research farm near Freeville. Late blight fungus was responsible for the Irish potato famine that killed a million people and caused many to emigrate, rather than starve. It destroyed the storage potatoes as well as the plants in the fields.
 |
| late blight Phytophthora infestans Gerald Holmes |
Several years ago, we had an outbreak of late blight that was atypically early, due to infected tomato transplants at the big box stores. Normally, late blight appears later in the growing season. It can wipe out farm fields of potatoes and tomatoes, as well as home gardens. Usually late blight overwinters only on living plant tissue such as potatoes left in the ground. It will not overwinter on frozen tomato plants, stakes, labels, or in the soil itself (yet). However, it is important to remove infected plants so as not to spread the disease.
Cornell researchers are hard at work, developing tomatoes varieties resistant to late blight. Several Tompkins County Master Gardeners are trialing ‘Iron Lady’ tomato this year.
So what about early leaf spots? Early blight and septoria are two fungus diseases that typically appear earlier in the season. These fungus diseases DO overwinter in the soil, so we recommend crop rotation. Tomatoes and potatoes are in the same plant family, so that is not a true rotation. For a list of vegetable plant families, please contact the GrowLine horticultural hotline for “Rotating Plants by Family.”
 |
Septoria on TomatoPaul Bachi |
Other tomato problems include fungus diseases, verticillium and fusarium, and nematodes. Many tomato varieties are labeled ‘VFN’, indicating resistance to these problems. Heirloom tomatoes may or may not have resistance, but seed companies don’t usually run tests to determine this.
Another frequent tomato problem which we don’t seem to have this year, is blossom end rot. This black blotch at the bottom of the tomato is caused by a calcium deficiency, which in turn is caused by uneven watering, which impairs calcium uptake by the roots. We see it more in dry years when gardeners either don’t water enough or often enough, or don’t apply mulch. If I plant deeply in my clay soil amended with organic matter, and mulch with rotten leaves, I never see blossom end rot.
Cool nights are to blame for the lack of ripe tomatoes this year. Try draping row cover over the plants to trap and retain some more heat. Let’s hope for warm weather in September!
Ask a Gardener appears weekly in The Journal during the growing season. For answers to other garden, lawn, landscape and pest questions, call Cooperative Extension at 607-272-2292 or email: growline1@gmail.com. This article was written by Patricia Curran, horticulture program manager at Cornell Cooperative Extension of Tompkins County.
