Most problems we see here truly are due to cultural issues such as poor soil preparation, watering or fertilizing. However, there are those times when a more serious problem causes the plant’s death before it fulfills your hopes for lots of tomatoes. There are two diseases of tomatoes we see in Grand County somewhat regularly — curly top, a fairly common problem that I have seen again this year, and early blight, which we bring on ourselves due to poor growing practices.
The most common serious tomato problem we see here is scientifically known as beet curly top virus (BCTV) and is spread by beet leafhoppers. And no, you don’t have to grow beets to have these pests. This virus has cropped up all over Grand County over the years. Usually it’s just a plant here and there in a garden or field, although I have seen large numbers in a single area killed before.
These leafhoppers are found in semiarid regions and pick up the virus from host plants, many of which are our range plants, such as kochia, Russian thistle, four wing saltbush and lambsquarter. The leafhopper usually comes through in the early summer, feeds on the small tomato plants that are common at that time, and while feeding injects the virus. By the time we see the effects, the leafhoppers have moved on. While normally we see this problem from early to mid-summer, later summer infections have happened in the past.
Infected plants start showing curling leaves, which feel thicker than non-infected leaves and often have darker colored purplish veins. The overall plant turns yellow and quits growing. Plants don’t recover and could be a source of re-infection. At that point in time there isn’t anything you can do about an infected plant other than pull it up. With curly top, often the only option is just hoping the leafhoppers don’t come visit your plants. Totally covering plants with a row cover, a specific material designed for the purpose of covering crops, is probably the best course of action if this is a continual problem year after year.
Another disease is early blight or Alternaria leaf spot. As the weather gets hotter an infected plant will start showing brown to black spots on the lower leaves of the plant, with some yellowing of the leaf often starting at the leaf end and edges. The leaves usually eventually turn completely yellow and drop off.
This fungus is most often seen when plants are too closely spaced and aren’t in cages and off the ground, causing the plants to receive less air circulation. Leaf spot also can occur when the plant foliage is being kept too wet.
Remove all the dead plant material since the fungus overwinters on this material, and don’t plant your tomatoes in the same spot each year. Since peppers and eggplants are in the same family, don’t plant them in the same spots year after year either.
Water and fertilizer problems
While there are other tomato diseases, gardeners in our area usually have to work harder to make them happen — although we do occasionally have people who succeed. All this being said, the most common tomato growth problems, including yellowing and browning of the foliage, are caused by poor watering and fertilizing practices. So water appropriately, spreading it out and watering deep but infrequently with the understanding that as the plant gets taller you will need to water longer and more often.
Also, to help keep problems at bay, encourage your tomatoes to grow vigorously, which requires appropriate but not excessive fertilization. While organic matter is great and should be added to the soil, it usually, by itself, doesn’t supply enough nutrients to achieve truly good growth.
Thought for the day: “A world without tomatoes is like a string quartet without violins.” —Laurie Colwin
Previous articles are available at The Times Independent website, www.moabtimes.com. Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at email@example.com.