Home Gardening

Two more common tomato problems
The Coast Gardener Newspaper and Web Column - June 8, 2002

Tomato plants suffer from a multitude of diseases and insects. I covered several tomato topics of interest last week, but gardeners are still having trouble with a couple more tomato problems. Both blossom-end rot and tomato spotted wilt virus are worthy of a lengthy discussion.

Blossom-end rot is caused by a shortage of calcium in developing fruit due to a lack of uptake of this essential growth element from the soil. Tomato plants growing in soil low in calcium, and those that are not properly irrigated, are more likely to produce fruit that will be affected. It's best to try and keep the soil moisture as even as possible and avoid letting the soil dry out before watering. Also, blossom-end rot is generally more severe when plants are fertilized too heavily with nitrogen; therefore, it is important to have a soil test analysis of your vegetable garden.

The problem occurs at any stage of fruit growth, but is most common on fruit one-third to one-half grown. The first symptom of blossom-end rot is a slight discoloration, water-soaked in appearance, occurring at the blossom-end (bottom) of the fruit. This area enlarges rapidly, producing a dark brown or black sunken area. The skin over the affected area becomes dry and leathery.

Since this problem is closely related to water supply, it's important to monitor soil moisture and irrigate before signs of moisture stress are apparent. As a general rule, tomato plants need at least one inch of water per week in the form of rain or supplemental irrigation. If your plants aren't mulched, consider doing so, since this practice will help maintain uniform soil moisture conditions. Apply several applications of formulated garden sprays containing calcium chloride if the disease begins to develop. This will help prevent further development of the problem, but will not cure fruit already affected.

Follow a recommended program of fertility and avoid excessive application of nitrogen fertilizer. Collect a soil sample to determine levels of calcium and correct any deficiency problem through application of lime this fall. Remove fruit showing symptoms of blossom-end rot when the problem is first observed. This practice will reduce the drain of food and nutrient materials which otherwise would be available for development of other fruit not affected by blossom-end rot.

Tomato spotted wilt virus disease is appearing in many home garden plantings. The virus attacks and causes disease in a wide range of 166 plant species, but tomatoes seem to be a favorite host. Spotted wilt infected plants exhibit a range of symptoms on foliage and fruit. However, the primary damage occurs on fruit that become discolored and develop irregular yellow blotches.

Blotched areas range in size from about one-fourth to occasionally one inch, or larger, in diameter and tend to be circular in appearance. Affected fruit are worthless since they fail to ripen properly and are unfit for fresh consumption or processing.

Early symptoms of the disease show up on tomato leaves, which generally have many small, dark colored spots on the youngest foliage. Infected leaves often develop a bronzed appearance, and the tops of plants sometimes take on a "bunchy" appearance since the disease slows top growth of infected plants.

Tomato spotted wilt diseased fruit are found on plants that were infected earlier in the season by the virus, as a result of thrips feeding. Thrips are tiny insects that pick up the virus from infected weeds and carry virus particles to tomato plants, which become infected during thrips feeding activities. In addition, peppers are susceptible to this disease.

How do you handle tomato spotted wilt virus disease? First, determine if you have a spotted wilt problem. Collect leaves from the top of the plant that seem affected and bring them to your local Extension office for diagnosis. Gardeners with tomato spotted wilt can't do much about the disease this season, but the following procedures may be useful in plantings carried out later this spring or in the fall garden.

Research has indicated the use of shiny mulch with an aluminum color around susceptible vegetables may cut down on thrips infestation, thus limiting chances for tomato spotted wilt virus to infect the plants. Apparently, light reflected from the mulch surface interferes with the ability of thrips to locate the tomato or pepper plant. The technique works best if highly reflective mulch is used.

A suggested approach is to spray or paint black plastic mulch with aluminum paint after the mulch has been installed. Best results are obtained if the technique is used early in the season at the time of transplanting.

Please note the reflective mulch should extend well beyond the transplants to afford protection as the plants increase in size. Before going to the trouble of painting black plastic, check with your garden supply dealer for availability of pre-silvered mulch. This type mulch is already available for commercial vegetable producers, and your local dealer could have this product in stock.

These archived gardening columns were written by Chance McDavid, former Harrison County Extension Agent.