June 16, 2011 - Armyworms mowing down rice in Jeff Davis Parish

7/26/2011 8:26:19 PM

Picture 1. Field suffering from armyworm infestation to the left of the levee and a healthy field to the right of the levee.

Picture 2. Cattle egrets (the white birds) and "trash birds" (the black birds) as they are called by my student worker. Birds are a good indication of an insect infestation.

Picture 3. Eddie Eskew (G&H) collecting armyworm caterpillars in an infested field.

Picture 4. Field of XL729 that is suffering from an armyworm infestation. The armyworms have been in the field for about 72 hours. Flood was applied about 24 hours after the initial infestation.

Picture 5. Many armyworm caterpillars feeding on a rice plant.

Picture 6. The armyworms were clustered onto the stubs of the plants, mowing them down to the surface of the water.

Originally posted June 16, 2011, by Natalie Hummel on Louisiana Rice Insects

I had planned to write about rice stink bugs today, but something else came up during our field work. Yesterday, at the Simon field site tour stop, Mr. Eddie Eskew told me about a field of rice that was suffering from a severe infestation of armyworms. Up to this point in the season, I’ve had a few calls about armyworms, but nothing out of the ordinary. We wanted to collect caterpillars to add to our lab colonies on campus, so we headed to the field today. I thought you would like to see what can happen when armyworms march across a rice field.

Last week this field of XL729 was progressing nicely. You can see in this picture how nice the surrounding fields are looking (Picture 1). The grower called Eddie on Tuesday when he found armyworms infesting the field. They had marched in from the treeline on the edge of the field and quickly progressed across to the field road. No appreciable damage was observed in surrounding cuts, although we did notice birds in a neighboring field, which were probably feeding on armyworm caterpillars (Picture 2). When we pulled up to the field it was not hard to observe the significant injury the armyworms were causing to the plants.

This particular field was planted in late April with the intention to harvest a rice crop. It will also be stocked with crawfish for harvest next spring. This creates complications when it comes to pest management. Insecticides which would effectively control the armyworms will be toxic to crawfish. For this reason, we cannot recommend any insecticides for control. If the armyworms were younger (most were large and probably near pupation) we would consider using Bt to control the population. The only measure that can be used is to bring flood water and drown them out. In this field, water had been on the field for about 48 hours and many of the caterpillars were still feeding on plants. On the positive side, they no longer had access to the crown of the rice plant. This is important for a rice plant because the leaves arise from the crown. You can think of this as being similar to your lawn. You can hit it with a mower and it will regrow every week (if we get any rain). This is also true for rice. Ideally we would not be mowing the rice plants; the plants that survive will likely be stunted. We collected some caterpillars to add to our lab colony (Picture  3). There is a good chance that most are either parasitized or will die of disease. This is what we typically find in field-collected armyworms. Unfortunately, the naturally occuring pathogens and parasitoids that attack armyworms in the field usually do not act quickly enough in a rice field to provide natural control and prevent severe injury. Following is a series of pictures of the field injury and caterpillars in the rice (Pictures 4-6).

On our way to the field I received a call from Kent Guillory, a consultant in Evangeline Parish, who also was treating a field infested with armyworms. I’d deduce from these two calls that it is now time to start keeping an eye out for armyworms. You can see from our observations at this field that they can move in and cause significant injury in as little as a day. If you can preserve the crown of the plant, it should be able to recover.

Tomorrow we will discuss rice stink bug infestations and management recommendations.

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