yellowing leaves on my tomato plants
For the last several years, I have had vigorous growth of my tomato plants early in the season, but as the fruit emerges and ripens the plant foliage beings to yellow and die from the bottom of the plant up. This year I had my soil tested and have top-dressed as directed, but it is happening again. I have heard this may be overspray from Roundup, etc. - however we have not used this at all. What is happening?
The yellowing can be due to environmental issues and some foliar diseases. This does not sound like a Roundup issue. It is normal for the lower leaves to yellow and decline. Remove them.
Tomatoes can be susceptible to several foliar diseases. Two common foliar diseases are early blight and septoria but it does not matter which disease it is because the management is the same. Select disease resistant varieties, remove the lower leaves to slow the upward spread of the disease, keep plants well mulched to minimize soil splashing, water at the base of the plants, provide adequate spacing, and spray with an organic fungicide (fixed copper) early in the season to lessen the spread of the disease. Fungicide treatments can help to protect new or un-infected foliage, they are not curatives. Remove infected plant material at the end of the season. See our website for more information on early blight http://extension.umd.edu/growit/early-blight-vegetables