Dectes stem borer

The Dectes stem borer (Dectes texanus) is a destructive pest belonging to the Cerambycidae family. Often referred to as a longhorned beetle, this insect has become a major concern for soybean producers, as its larvae feed internally on plant stems, causing significant physiological and structural damage to the crop.

While soybeans are the primary host, Dectes texanus is known for its polyphagous behavior. It can thrive on various wild legume species, as well as on commercial crops like sunflowers and common weeds such as ragweed, which serve as alternate hosts and facilitate the spread and persistence of the infestation across agricultural landscapes.

The lifecycle of the borer is closely tied to the soybean growth cycle. Adults emerge in early to mid-summer, mating and laying eggs in soybean petioles. Upon hatching, the larvae bore into the main stem of the plant. Throughout the summer, they feed on the pith, moving downwards toward the base of the plant to prepare for overwintering, where they remain inside the stubble.

The economic impact of the pest is two-fold. Firstly, internal feeding weakens the plant's vascular system, which can result in reduced seed size and overall yield loss. Secondly, the most devastating impact is the girdling of the stem base as the larva prepares for winter. This causes the stems to lodge (break) under mild wind pressure, making mechanical harvesting extremely difficult and resulting in heavy grain loss.

Management of Dectes texanus is challenging due to the protected location of the larvae. Recommended control strategies include:

• Tillage practices that incorporate crop residues to increase larval mortality.
• Early harvesting of soybean fields to minimize losses from lodging.
• Judicious use of foliar insecticides timed to coincide with adult activity.
• Vigilant weed management to eliminate alternative hosts along field edges.