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Pest Facts<br />
• Common names: <strong>Dectes</strong> stem borer, soybean stem<br />
borer<br />
• Latin name: <strong>Dectes</strong> texanus, family Cerambycidae<br />
• Description<br />
• Adult: gray-colored beetle with long black-and-gray<br />
banded antennae; length is ½ inch (13 mm)<br />
• Larva: creamy white to dull yellow in color, without legs,<br />
½-inch long with “accordion-style” segments<br />
• Egg: very small, white-colored egg laid inside soybean<br />
petiole where female cuts a scar (see photo on back)<br />
Adult <strong>Dectes</strong> stem borer<br />
Larvae of <strong>Dectes</strong> stem borer<br />
<strong>Pioneer</strong> Agronomy Sciences<br />
<strong>Dectes</strong> <strong>Stem</strong> <strong>Borer</strong><br />
Injury and Pest Symptoms<br />
Pest Status and Importance<br />
Larva in soybean stem<br />
• Larvae damage soybeans by: 1) tunneling inside the<br />
stem and reducing yield production capacity, and 2)<br />
girdling, which causes plants to lodge<br />
• Larvae girdle stem one to two inches above soil line<br />
• Girdling, and subsequent lodging, are most severe in<br />
early planted, short-season soybean varieties<br />
Soybean stems girdled by larvae<br />
and tunnels plugged with frass<br />
• Minor soybean pest in most states, but fields in<br />
some areas may have ≈100% of plants infested<br />
• Yield losses range from 7 to 12% in individual plants<br />
• Girdled plants may snap off at slightest pressure,<br />
causing plants to lodge prior to harvest<br />
®, SM, TM Trademarks and service marks of <strong>Pioneer</strong> Hi-Bred. © 2012, PHII
Life History<br />
• Larvae pupate in the spring inside soybean stem<br />
• Adults emerge from stems during late June to late<br />
July in Kansas<br />
• Adults may live to September<br />
• Sunflower is the preferred host; cocklebur and giant<br />
ragweed are also used as larval hosts<br />
• Soybean is a secondary host for larvae<br />
• Adults live an average of 23 days on soybean, but<br />
53 (males) and 76 (females) days on sunflower<br />
• Females lay eggs primarily in leaf petiole<br />
• Larvae tunnel down leaf petiole and into main stem<br />
• Larvae complete four stages<br />
• Larvae create an internal girdle of the stem near soil<br />
line and plug the tunnel below the girdle with frass<br />
• Larvae are cannibalistic; only one larva overwinters<br />
in base of stem<br />
• One generation occurs per year<br />
Not Sampled<br />
0%<br />
0.1 - 10%<br />
10.1 - 25%<br />
25.1 - 50%<br />
> 50%<br />
<strong>Dectes</strong> stem borer distribution in soybeans in the lower<br />
Mississippi Valley (Tindall et al. 2009. J. Insect Science)<br />
<strong>Pioneer</strong> Agronomy Sciences<br />
Origin and Distribution<br />
• Native to North America from Atlantic seaboard to Great<br />
Plains; primarily a pest in central Great Plains and lower<br />
Mississippi River Valley<br />
Integrated Pest Management Practices<br />
• Harvest: the most practical method of reducing yield<br />
losses is to harvest heavily-infested fields as soon as<br />
possible to minimize lodging loss<br />
• Planting time: avoid early planting with short-season<br />
varieties in areas with known problems<br />
• Insecticides: often ineffective against adults (extended<br />
emergence period) and larvae (protected inside stem)<br />
• Plant resistance: no known resistant soybeans<br />
• Cropping pattern: avoid crop rotation into commercial<br />
sunflowers infested the previous year<br />
• Tillage: disking or burying infested soybean stems after<br />
harvest can reduce subsequent populations<br />
Photos and Text<br />
Egg scars on<br />
soybean stem<br />
% infestation<br />
in fields<br />
> 50%<br />
20-40%<br />
< 10%<br />
<strong>Dectes</strong> stem borer distribution and percent infestation<br />
in Kansas soybeans<br />
(modified from Buschman & Sloderbeck. 2010 J. Insect Science)<br />
Marlin E. Rice, DuPont <strong>Pioneer</strong><br />
Reviewed by Phil Sloderbeck (Kansas State University),<br />
and Paula Davis and Herb Eichenseer (DuPont <strong>Pioneer</strong>)<br />
®, SM, TM Trademarks and service marks of <strong>Pioneer</strong> Hi-Bred. © 2012 PHII
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