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Soybean Stem Borer

Look for holes where the petiole meets the main stem.  This is the entry point where stem borer eggs are laid and later hatch into larvae.

Are you noticing holes in your soybean stems?  Holes where the petiole meets the main stem are the entry point where soybean stem borer (also known as Dectes stem borer) larvae tunnel into the main soybean stem.  Originally eggs are laid in soybean leaf petioles in the upper canopy.  The eggs hatch into larvae which burrow down the petiole then into the main soybean stem.  Notice the soybean stem borer infected stem in the middle while the soybean stem to the right has a a non-infested area where the petiole dropped (it is naturally sealed over by the plant).  Count how many plants out of 20 have this symptom to get an idea of percent infestation and repeat in several areas of the field.  Fields with 50% or more infestation need to be harvested first and perhaps earlier to avoid lodging and yield loss associated with lodging.

Lodged soybeans can be another key for checking for stem borer around harvest time.  Notice the stem in the middle of the photo that is lodged.

Lodged soybeans can be another key for checking for stem borer around harvest time. Notice the stem in the middle of the photo that is lodged (fallen over instead of standing in the row).


Following the stem to the base, the stem easily breaks away from the plant. The stem itself will appear solid. The base of the plant where it breaks is also often sealed off. The stem borer will seal itself inside the base of the stem. In this case, there’s a small portion that hasn’t been sealed off yet.

Gently pulling apart the base of the stem reveals the soybean stem borer larva beginning to pupate.  The larva will spend the winter pupating here and emerge as an adult beetle next year.

Gently pulling apart the base of the stem reveals the soybean stem borer larva. The larva will spend the winter and eventually pupate here.  Adult beetles will emerge in late June and there’s only one generation per year.  For more information specific to life cycle and management, please see the following NebGuide.

Harvest #Soybeans at 13%

In spite of green stems and even leaves on some plants, soybeans are surprisingly drier than what you may think.  I’ve been hearing reports of soybeans in the 7-10% moisture range already in spite of there also being some “lima beans” along with the low moisture beans at harvest.

Harvesting soybeans at 13% moisture is a combination of skill and maybe some luck.  Why is 13% so critical?  A standard bushel of soybeans weighs 60 lbs. and is 13% moisture.  Often beans are delivered to the buyer at lower moisture than 13%.  The difference between actual and desired moisture content will result in lost revenue to the grain producer.  Here’s how the loss works based on UNL Extension’s “10 Easy Ways to boost profits up to $20/acre”:

  • Since 13 percent of the weight is water, only 87 percent is dry matter. The dry matter in a standard bushel is 52.2 pounds and the remaining 7.8 pounds is water.
  • If this bushel of soybeans is kept in an open basket and some moisture is allowed to evaporate, the net weight of beans would decrease. If the dry matter weight remains unchanged at the standard 52.2 pounds, the wet basis weight for any moisture content can be calculated.
  • For example, a standard bushel at 13 percent moisture weighs 60 pounds. If the moisture content were reduced to 11 percent (89 percent dry matter), the wet basis weight per bushel of the soybeans would be 52.2 pounds of dry matter divided by .89=58.65 pounds. (1.35 pounds less than the standard 60 lb. weight of beans initially placed in the basket). For each 52.2 pounds of dry matter delivered at 11 percent moisture, you miss an opportunity to sell 1.35 pounds of water.
  • It is standard practice for buyers to assume 60 pounds of soybeans constitutes a bushel when soybeans are at or below 13 percent moisture. When the beans are below 13 percent, the difference in water content is made up for by an equal number of pounds (wet basis) of soybeans.
  • Assuming a 60 bushel per acre yield and selling price of $8.50 per bushel, the potential extra profit the producer could realize if the beans are harvested at 13 percent moisture instead of 11 percent is $11.48 per acre.

Rapid dry-down and difficulty harvesting green stems and pods are the most common reasons for harvesting at lower than standard moisture. The following practices can help producers maintain quality and expected moisture content.

  • Adjust harvest practices. When harvesting tough or green stems, make combine adjustments and operate at slower speeds.
  • Begin harvesting at 14 percent moisture. Try harvesting when some of the leaves are still dry on the plant; the beans may be drier than you think. Soybeans are fully mature and have stopped accumulating dry matter when 95 percent of the pods are at their mature tan color.
  • Plan planting dates and variety selection to spread out plant maturity and harvest.
  • Avoid harvest losses from shattering. Four to five beans on the ground per square foot can add up to one bushel per acre loss. Harvest at a slow pace and make adjustments to the combine to match conditions several times a day as conditions change.
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