Ask Your PCA: How important is beet armyworm control in tomatoes?

Issue Date: September 17, 2008

Nick Groenenberg

By Nick Groenenberg, Agricultural Consulting, Hanford PCA, CAPCA member

California tomato growers are well aware that when beet armyworms enter the fruit and fungus gets in, the fruit frequently can't make grade. That's why it is so important to keep these worms out of your tomatoes.

I begin monitoring for beet armyworms as soon as the tomato plants start growing. The greatest damage comes when the worms enter the fruit, but they can also attack the leaves. It becomes more urgent to monitor once the fruit starts to form. And the most critical time is the last 45 days before harvest. I monitor by looking for signs of feeding, or for egg masses, being laid by the beet armyworms.

The growers I work for don't tolerate any of these worms--when we see egg masses, we apply. I handle processing tomatoes but I think that it would be even more urgent to keep these worms out of your fruit if you are growing fresh market tomatoes.

The University of California Pest Management Guidelines advise checking with your processor for acceptable levels of armyworm-scarred fruit. In fresh market tomatoes, the presence of such holes results in unmarketable fruit.

The UC guidelines advise sampling when fruit appears. A five-minute timed search is useful in determining the need for treatment. On average, if one or more larvae or egg masses are found in five minutes, treatments may be justified, according to the UC guidelines.

We rotate because we want to save our materials. We want to make sure that what we apply is efficacious and we rotate materials so they stay that way. Knockdown speed is important because you like to see the worms stop feeding very quickly after you apply.

Residual is important, too, so you don't have to apply as often. We are getting two to four weeks' control with the newer materials. This residual is a lot better than we were getting with the older materials.

The newer materials are pretty soft chemistries. They are generally easier on the environment than some of the older materials. They are also easier on the beneficial insects. I don't see as many outbreaks of secondary pests as I used to.

No matter what you use to control them, you have to keep watching for beet armyworms right up to the end of your harvest. They can sneak up on you pretty quickly.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item. Top