Weekly Express-News Article

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.

 

            Blossom end rot is showing up on tomatoes now.  The symptom, a black flat area at the bottom of the fruit looks like a fungus, but it is not.  Blossom end rot is a physiological problem resulting because the plant did not take up enough calcium during the fruit’s development.  The calcium deficit resulted because the water flow into the plant was broken at some point.  The calcium is transported in the water flow. 

 

            The break in uptake of water usually occurs when the soil dries out or there is a point when transpiration (water flow out of the leaves) is greater than the roots ability to pull up water.  The typical situation is when the temperature goes from cool to hot in a space of a day or two.

 

            Reduce the chance of blossom end rot by enriching the soil with compost for better moisture retention, by using drip irrigation everyday and by mulching over the root system with live oak leaves.  Fruit with the blossom end rot symptom is not attractive, but it can be consumed.  Just cut off the bad end of the fruit.