Green Cloverworm, Soybean Looper And Alfalfa Caterpillars Observed In S.D. Soybeans

 

Throughout South Dakota we are beginning to notice a lot of small green caterpillars in soybean fields. Currently, these caterpillars aren’t causing too much defoliation due to their small size, but as they grow their feeding may become more noticeable.

 

 

The three most commonly observed green caterpillars in soybean are the green cloverworm (Figure 1), cabbage or soybean looper (Figure 2 and Figure 3) and alfalfa caterpillars (Figure 4). In some fields, two or three of these species may be observed simultaneously.

 

Although these caterpillars are generally not severe pests of South Dakota soybean, their presence is important when other defoliators may also be present within the field. If only one defoliator species is present in high populations it may be possible to determine thresholds for it, however, when multiple defoliator species occur in a field we recommend looking at the average cumulative defoliation within the field.

 

 

 

 

 

 

The three caterpillar species are all very similar in appearance. That is, all three species are green and have white stripes that run the length of their bodies. The easiest way to discern the green cloverworm, soybean/cabbage looper and alfalfa caterpillars from one another is to look at the number of abdominal prolegs they have.

 

 

Not familiar with abdominal prolegs? All caterpillars will have three pairs of true legs, which are present near their heads. In addition, caterpillars have one pair of legs at the end of their bodies, which are referred to as the anal prolegs. The remaining legs in the middle of their bodies are the abdominal prolegs (Figure 5). The number of pairs of abdominal prolegs differs depending on the species of caterpillar.

 

The green cloverworm caterpillars have three pairs of abdominal prolegs. The soybean looper and cabbage looper caterpillars each have two pairs of abdominal prolegs. The alfalfa caterpillars have four pairs of abdominal prolegs. Of the three species, the green cloverworms have the greatest potential for being serious defoliators in South Dakota, but all three species may be present and will feed on leaf tissue.