Tag Archives: soybean

Will Slugs Be A Problem in 2013?

Slugs are not a new problem, but they continue to be an unpredictable one.  It seems that they show up when and where we least expect them and never show up when and where we do.  But considering the cool and wet weather we’re experiencing, we should be on the watch.

The photo below was taken last May, 5 days after planting in a no-till field with a rye cover crop.  Stand was about half of what was expected and feeding scars could be seen on the hypocotyl and cotyledons.  When digging in the seed furrow, slugs were more often present than not.

Slug Damage Soybean

Cold, wet weather slows seedling growth; therefore reducing the plant’s ability to outgrow slug damage.  Slugs will feed on all crops, taking large chunks out of the stem and sometimes cutting the plants like a cutworm.  They feed mostly at night although I’ve seen them feeding during cloudy days (see photo below).  In general, they are more of a problem in wet, poorly drained fields or in low-lying portions of fields.  Still, we’ve seen them on hilltops.  Slug on SoybeanThey are usually a problem in no-till fields with high residue crops such as corn or grain sorghum and/or in fields the slug underneath last year’s corn stalk.  If the seed furrow doesn’t fully close, slugs will follow this “highway” and eat seedling after seedling before it emerges from the soil.

Slug Under corn residueWhat can be done about this problem?  First, scout the field before you plant, paying close attention to poorly drained or low-lying portions of the field.  If you find slugs, you have a couple of options.  One is to not plant and wait for warmer and dryer weather.  Slug damage usually disappears under warm and dry conditions.

Another alternative is to apply the slug bait/molluscicide, Deadline®, which contains the active ingredient metaldehyde.  It is sold at Deadline® M-Ps™ Mini-Pellets (colored with a blue dye) and Deadline® Bullets (dye-free).  This is the only reliable treatment that we have available.  It must be spread evenly at 10 to 40 lbs per acre over the infested area.  The product is fairly expensive, so the 10 lb rate is the most common and has worked well in my experience.  The product is not commonly stocked by local retailers, so it can be hard to find.

Will slugs be a problem?  Maybe.  Maybe not.  But, with the current weather conditions, I’d suggest scouting those slug-prone fields.

Full-Season Soybean Seeding Rates

My soybean seeding rate recommendation for full-season production systems is to plant enough seed to insure 80,000 uniformly spaced plants/acre.  If you cannot uniformly space the plants within a row, then my recommendation rises to 100,000 plants/acre.  Based on numerous seeding rate experiments conducted in Virginia, I feel very confident in this recommendation.

Of the 27 full-season seeding rate experiments conducted from 2004 to 2009, I can group soybean yield response to plant population into the following three categories: 1) no response to plant population; 2) optimum plant population of 75-100,000 plants/acre; and 3) optimum plant population of 100-140,000 plants/acre.  Below are individual tests that represent these categories.

Full-Season Seeding Rate Study - Virginia

First, note that these examples only show the response of yield to plant population and do not take into account seed costs.  When seed costs are included, the optimum plant population is lower than is shown on the graphs.  Also note that these graphs show yield response to plant population, not seeding rate.  To convert to seeding rate, adjust these numbers to reflect your expected percent emergence.  For example if you assume 75% emergence, you would need to adjust your seeding rate to 133,000 seed/acre to obtain 100,000 plants/acre.

We conducted these experiments with maturity group 4 and 5 varieties.  While one may think that more seed might be required for early-maturing varieties, this was not the case (i.e., group 4 and 5 varieties responded similarly).

There may be some correlation with yield potential as listed below:

  • 30-40 Bu/A Yield Potential (14 tests)
    • 6 required 100-130,000 plants/acre
    • 2 required 70-100,000 plants/acre
    • 6 had no yield response
  • 40-60 Bu/A Yield Potential (7 tests)
    • 2 required 70-100,000 plants/acre
    • 5 had no yield response
  • > 60 Bu/A Yield Potential (7 tests)
    • 2 required ~130,000 plants/acre
    • 4 required 70-100,000 plants/acre
    • 1 had no yield response

So, what do these data mean?  It means that every environment (year & location) is a little different and there is no way that we can predict with 100% accuracy the exact seeding rate that will be required for your field in the coming growing season.  However, we do know that if we can obtain full canopy closure (90-95% light interception) by full flower (R2 stage) to early pod (R3 stage), we can maximize soybean yield potential.  In a dry year or under a droughty soil (low yield potentials), greater seeding rates will help insure this.  Still in most cases (30 to 60 bushel yield potentials), 70-100,000 plants/acre are adequate.

What about fields with greater than 60 bushel yield potential?  In this case, we need to look beyond adequate leaf area and need to start thinking about how many pods the soybean plant can support.  For instance, at 40 bushels/acre and 100,000 plants/acre, we only need to produce 72 seed/plant (using 3000 seed/lb) or about 30 pods/plant (using 2.5 seed/pod).  But, at 60 bushels/acre, we need to produce 108 seed or 45 pods per plant; at 80 bushels/acre, we need 144 seed or 60 pods per plant.  Considering that 12 reproductive nodes per plant are possible, 4 to 5 pods per node on a rather tall plant would be required.  Although branching will also contribute to yield, that seems a lot to ask of one soybean plant.  So, if you are trying to win the yield contest or are irrigating soybean, I suggest planting enough seed to obtain 120-140,000 plants per acre in a full-season system; otherwise 80-100,000 plants are adequate.

Now is a Good Time to Evaluate Your Varieties for Foliar Diseases

September is a great time to evaluate your crop and the performance of varieties that you chose.  In addition to general growth and health of the crop, take some time to determine if you have any of the below diseases.  If so, you could be losing some yield.  If you sprayed with a fungicide and still have disease, reconsider the product and rate used and the time that the fungicide was applied.  Keep in mind the weather conditions when the application was made and the conditions 2 to 3 weeks after or before the product was applied.  Cool temperatures (70’s) and high relative humidity (>95% for 12 hours or more) will usually increase disease incidence.

Another caution is to never diagnose a specific disease on the plant without verifying it with a person trained to identify plant pathogens.  Only when the reproductive structures are found on the leaf can a disease be confirmed.  Many things will cause look-alike symptoms.  Be sure before you cast the blame.  There are more diseases than just the ones shown below, but these are the most common.  Brown spot is normally found in the lower part of the crop canopy (the lower leaves), Cercospora blight and leaf spot will be found throughout the canopy, and the frogeye leaf spot and downy mildew tend to be found in the upper part of the canopy.