Ask Mr. Smarty Plants

Lycopersicon esculentum, tomato, is native to South America, a member of the Solanaceae, or Nightshade, family. Since its early cultivation by prehistoric natives of South America, it has moved northward through Mexico and is one of the most hybridized of all plants. Both of these facts remove them from our area of expertise. The Lady Bird Johnson Wildflower Center is dedicated to the care and propagation of plants native not only to North America but to the area in which the plant is being grown. Although the tomato plant is out of our field, we would like to mention that planting anything in the summer in Texas in black plastic is dangerous, in terms of the soil heating. That black plastic really conducts the heat into the soil, and plants are accustomed to being grown in soil kept cool by the insulation of all the earth around it and sun only hitting the surface. That's just a thought, we have no expert proof, but we know we have fried plants we left in the black plastic from the nursery in the sun. 

For some help from some experts who actually know what they're talking about, read this website from Cornell University Horticulture by Stephen Reiners, Ten Mistakes to Avoid When Growing Tomatoes.  Another good article is from Northern Gardening.com Growing Healthy Tomatoes by Terry L. Hockey.  In terms of spraying the Sevin on the plants, have you seen and identified any bugs on your tomatoes? Read this article from Living With Bugs.com Sevin (Carbaryl) Insecticide.  Before you fix something, find out what the problem is.