The Q&A Archives: Tomatoes with Mold on Stem

Question: I planted tomatoes plants from seed last year. The plants did excellent -- I put them in my greenhouse...still excellent -- pruned...etc. they were producing large amounts of tomatoes. Some fell off the vine with moldy stems; at harvest time we picked the green to ripen inside (normal for AK). My tomatoes molded at the stem area before getting ripe. My mother bought her plants from a nursery and her plants did not mold -- they just ripened...
Was it my seeds, dirt or what? Was it disease? I did not use any chemicals at all on them only fertilizer in the water. I am trying your seeds this year and do not want to run into the problem again.

Answer: Tomatoes are very hardy plants, however, under certain circumstances various diseases can attack them. Your description sounds as if the tomatoes had some type of fungal or bacterial disease. Diseases are difficult to diagnose since many have similar symptoms. Yours could be Gray mold which is a common cause of fruit rot, and often appears as a stem rot. However, other fungal or bacterial diseases are also possibilities. To prevent this in the future, buy disease resistant plants. They are distinguished by the letters after the variety name, such as Celebrity VFFNTA where the initials stand for resistance to: A, Alternaria (early blight); C, Clodisporium (leaf mold); F, Fusarium wilt, race 1; FF, Fusarium wilt, races 1 and 2; N, Nematodes, S, Stemphylium (Gray leaf spot); T, Tobacco Mosaic Virus; V, Verticillium wilt.

The extra humid conditions of greenhouse growing could also be a factor in your problems. Good air circulation and warm dry air are best for tomatoes. Over fertilization could also be a contributing factor. Give your plants reasonably fertile soil, well-drained and high in organic matter, a consistent supply of clean, air-temperature water, and occasional minimal feeding without overfeeding. Go easy on the nitrogen which can worsen many diseases and disorders. Try not to wet the leaves, water the ground only, and do not work among the plants when wet. Mulched plots have fewer fungal outbreaks, because mulches prevent soil-borne fungi from splashing onto the lower leaves. Be sure not to plant in the same soil that was previously planted with tomatoes or any members of their family: potatoes, eggplants or peppers. A homemade spray made from 1 teaspoon of baking soda in a quart of water may help control fungal disease.

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