Dectes stem borer is a soybean stem boring insect pest that can cause severe lodging and yield reduction.


Life cycle- Dectes Stem Borer
Dectes texanus texanus
The Dectes stem borer is believed to have one generation per year.  Adult stem borers emerge in late June through early August, and will feed on stems and petioles of soybeans, leaving a feeding scar. Female adult stem borers will chew a hole into the petiole or stem where a single egg is laid.  After hatching, the larvae bores into the soybean petiole or stem and tunnels to the main stem.  The stem borer larvae feeds on pith until it matures reaching 1/2 to 3/4 in length.  In late summer, the stem borer larvae burrows down to the base of the soybean plant and girdles the inside of the soybean stem.  This girdling can be from ground levelup to 3 inches high and will make an over wintering site inside the stem.  The top of the stem where the stem borer over winters will be packed with chewed up plant debris and frass.  In the spring, the over wintering larvae will pupate, pupae will turn froma yellowish tan to dark brown before hatching and emerging as adults again in summer.  Domestic sunflower is a freferred host, so areas that produce both soybeans and sunflowers can be ideal regions for heavy infestations in both crops.  Other hosts can include wild sunflowers, cocklebur, ragweed, coreopsis, and woolley croton.

Damage, Thresholds and Treatment
Dectes stem borer damage is the result of the interior girdling of the soybean stem resulting in snapped off, lodged soybean plants prior to harvest with high winds in the fall.  Reports of 30 to 50% lodging of soybean plants just prior to harvest (R8-fully mature soybeans) are quite common.

Start scouting for adult stem borers starting in late June through August.  Sinse they overwinter in stoybean stems, fields with No-till or reduced-till soybeans or sunflowers have a higher probability of being a better over wintering site for stem borer larvae.  Thresholds have been difficult to establish and currently are associated with the emergence of adult stem borers.  If you catch 1 Dectes stem borer adult (beetle) per 10 sweep, data has shown that treatment is needed and a timely application of an insecticide can provide a positive yield response.  (Kansas State University)

Once thresholds have been reached the timing of a Hero EC application can begin.  Research has shown the ideal time to threat for stem borer is approximately 21 days after first emergence of stem borer adults. This timing allows for maximum adult emergence to occur, but before peak egg-laying occurs.  Hero at 4-5oz/A rate has been shown to provide excellent control of Dectes stem borers and protect soybeans yields.  The residual properties of Hero insecticide provide lasting control of stem borer as well as other insects including grasshoppers, podworms, stinkbugs, bean leaf beetle, soybeans aphids, webworms and other pests. 

Hero-Soybean Stem borer Applications
 

• Use Rate: 4.0-5.0 oz/A
• Application Timing:  Approximately 21 days after first adults emerge.
• Treatment threshold: 1 adult/10 sweeps with sweepnet.
• Application: 2-3 gpa by aerial, 10-20 gpa by ground.
• Re-entry interval-12 hours.
• Pre-harvest interval-21 days.
• May be tank-mixed safely with fungicides or herbicides.  Follow all label recommendations and restrictions for companion products.