Weekly Express-News Article

“San Antonio Life”

By Calvin R. Finch, PhD, SAWS Water Resources Director, and Horticulturist

Saturday, May 10, 2008

“Tomato Pests”

            Tomatoes are our favorite vegetable to grow in South Texas.  Controlling tomato pests and diseases can be quite a chore.  Here are descriptions of some of the problems and how to control them.

            Stink bugs come in several versions.  They all seem to have angular-shaped bodies and have the look of alien creatures.  As the name indicates they also stink when they are squashed. 

            Stink bugs inject digestive juices into the fruit and ingest the resultant “soup.”  The result of feeding stink bugs is misshapen, scarred fruit.  Stink bugs fly and are large so are difficult to control.

            If you have a small garden, collecting stink bugs by hand everyday is a relatively good way to control them.  I prefer carbaryl (Sevin) or Malathion.  A weekly spray works well.

            Spider mites become a real problem on tomatoes when the weather becomes hot.  The generation time of the tiny sucking insects becomes as short as four or five days.  Spider mites feeding cause the leaves to have a dusty faded look.  In severe infestations, tiny webs cover the plant.  There are several good organic controls for spider mites.  Seaweed spray applied twice per week does the job.  The new product Spinosad (Conserve and other product names) also seems to work.  Neem oil is labeled for spider mites, but I have not found it very effective.  Kelthane was the manufactured insecticide that was very effective for spider mites.

            To determine if you have spider mites, flick a leaf with your forefinger over a white piece of paper.  You should be able to see the red pinhead size mites moving on the paper.

            There are several worms that feed on tomatoes.  Pinworms enter the fruit and feed inside the tomato.  Hornworms feed on the foliage and may also eat the fruit from the outside.  Bt products such as Thuricide, Bio Worm Control or Dipel are effective, but only last five days.  Spinosad is also a good caterpillar control.  Spray it every week. 

            Early blight is the fungus disease that kills the stems from the bottom and works its way up.  The leaves turn brown and few fruit develop if the disease affects the plant early in its life. 

            Early blight control is achieved by spraying Chlorothalonil on the plant every week.  Chlorothalonil is the active ingredient in “Garden Disease Control” and other products.