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JenREES 10/2/22

Crop Update: What beautiful weather! Grateful for the crops that are being harvested! Also, grateful to hear some are blowing out combines after harvest in these heavily infested palmer fields before moving to the next field. That’s the first step in managing palmer for the future. Regarding combine cleanout, Market Journal had a video at: https://youtu.be/UtSAaWtMTS4 and CropWatch had an article at: https://go.unl.edu/skfh if you’d like more information.

Managing heavy palmer fields after harvest: Palmer and waterhemp seed survive for 5-7 years. With each plant producing an average of 500,000 seeds, it only takes a few plants to create a mess.

Heavy palmer pressure in hail damaged corn field.

It’s been encouraging to see the rye and other small grains being drilled in fields; I realize it’s also been hard to irrigate them up after such a long irrigation season. Small grains such as rye, wheat, and oats have been proven to significantly reduce palmer, even in the absence of residual herbicide use compared to a no cover crop control. With the addition of a residual herbicide, there was no difference between using a cover crop and the check treatment. However, the way I look at it, the cover crop was another tool to take some of the pressure off the herbicide from having to do all the work. The main reason for that is because these small grains keep the soil surface covered. Palmer germinates when it senses red light on a bare soil surface, so keeping the soil covered can help reduce early season palmer germination. The small grains are also beneficial at reducing diseases such as white mold and sudden death syndrome.

If one isn’t interested in cover crops but is already using reduced tillage, another plan going forward will be to use a PRE- herbicide with residual followed by POST- with residual and get to canopy closure. Essentially, the strategy there is to keep the seeds from germinating.

For those who plan on disking, the research showed that disking once and not disking again for 3 years resulted in palmer reduction of 80-100% by year 3. However, disking each year allowed the seed to keep coming to the surface where it could germinate (depending on the herbicides and timing used). So, planting a cover crop after disking to cover the soil is one option to help reduce palmer germination in the spring. For those not interested in cover crops, having a strong herbicide program of a PRE- with residual followed by a POST- with residual sooner than you think you may need it, may be a strategy. One can also include cultivation followed by a residual herbicide, depending on canopy closure. The use of tillage, flaming, and electrocution are also being used in organic and some conventional systems.

Finishing Replant Crops: Grateful to be at this point in the season where much of the replant corn is 1/4 milk or further! Hybrids will vary regarding growing degree units (GDUs) to finish. A GDD tracking tool to help is https://mygeohub.org/groups/u2u/purdue_gdd. Regarding irrigation, below is the amount of water needed to finish corn. Most of the beans should be close to done for irrigating.

  • Beginning dent needs 5.0” water, around 24 days to maturity, 25-55% yield loss potential.
  • ¼ milk needs 3.75” water, about 19 days to maturity, 15-35% yield loss potential.
  • ½ milk needs 2.25” water, about 13 days to maturity, 5-10% yield loss potential.
  • ¾ milk needs 1.0” water, about 7 days to maturity, around 3% yield loss potential.

We knew replant crops would be a target for insect and disease pressure. It’s hard to see the corn earworm impact crops for such a large area as what they have this replant corn. Even fields that were sprayed once still have ear damage on a good 50% of the plants. The earworm feeding has allowed entry of fungi such as those causing white/pink Fusarium ear mold to varying degrees on the ears. Also seeing some blue-gray Penicillium ear mold and some sprouted kernels. Unfortunately, there wasn’t much we could practically do about it and there’s nothing we can do now till harvest. The presence of mold does not automatically mean the presence of mycotoxins. For harvest, it’ll be important to set combines to blow out any lighter, damaged kernels. Will share more on grain management in storage later.

Stem Borer: Have heard some disappointment about soybean yields which I feel is mostly due to beans being pushed too fast with the weather. Soybean stem borer is also being blamed, but it hasn’t been proven via research to reduce yield unless beans become lodged/break off. To understand why, it’s important to understand corn and soybean physiology. Soybeans are dicots like trees and the xylem and phloem are found in rings towards the outside of the stem instead of the center. So the stem borer hollowing out the soybean center doesn’t affect the soybean vascular bundles, but insects like gall midge working on the outside of the stem can. This differs from monocots like corn where the xylem and phloem are arranged throughout the stem. Thus, I don’t think stem borer is the reason for lower soybean yields that weren’t due to lodging/breaking off this year.


Dicot vascular bundles of xylem and phloem are arranged in a ring, whereas monocot bundles are sporadic. Diagram via Plants Grow Here. https://plantsgrowhere.com/blogs/education/monocots-vs-dicots-with-diagrams

Wheat and oats significantly reduced palmer biomass compared to no cover crop alone in the absence of a residual herbicide (black bars). Utilizing a residual herbicide (gray bars), the wheat and oat cover essentially eliminated palmer biomass and there was no difference between those treatments and the no cover crop with residual herbicide treatment.

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).

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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.

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