By Scout Nelson
Dectes stem borer adults are now active in soybean fields, especially in southeastern areas where they’ve been a problem in the past. This insect pest can cause serious yield losses if not managed.
The Dectes stem borer lays eggs in soybean stems. When the larvae hatch, they tunnel through the plant, weakening it from the inside. As the plants mature and begin to dry, the larvae move to the base and chew around the stem. This damage can cause up to 17% of the infested plants to fall over before harvest, leading to significant losses.
Some fields in recent years have seen infestation rates as high as 70% to 100%. Because of this, fields with a history of Dectes damage should be scouted throughout the summer.
The best time to treat is between the first and third week of July. Research from 2024 shows that one application of Hero insecticide during this period can protect yields. Soybeans treated with Hero yielded 9.1 more bushels per acre than untreated fields. This added value comes to about $66.89 per acre, even after the cost of the insecticide and application.
Another option is to apply Hero first, then Vantacor about two weeks later. This method showed a $28.69 per acre benefit. Applying Vantacor alone twice gave only a small benefit of $2.57 per acre.
Other insecticides like Elevest and Brigade 2EC are also labeled for Dectes stem borer but were not as cost-effective in recent trials.
Photo Credit: istock-fotokostic
Categories: South Dakota, Crops, Soybeans, Harvesting, Sustainable Agriculture