Early-Season Considerations in Peanut – Inoculants

Brendan Zurweller, Extension Peanut Specialist, Mississippi State University
By Brendan Zurweller, Extension Peanut Specialist, Mississippi State University May 6, 2014 15:48

Quick Points:

  • Soybean and peanut inoculant are NOT the same.  Make sure the product is designed specifically for peanuts and that it is a true inoculant.
  • Inoculant products contain living organisms.  Store in a cool, dry place out of direct sunlight.  If using a liquid product, use non-chlorinated water as the carrier and make sure the tank is clean prior to use.
  • Mix up only enough product for what you will use in a single day
  • Inoculants are a necessity for new ground or ground that has been out of peanut for 4+ years.  It is inexpensive insurance on all ground, especially if that ground has been saturated for extended periods
  • Most liquid products are compatible with numerous in-furrow fungicides and other products for a specific time period.  Consult the label, company representative, or myself with compatibility questions.


Peanut had never been planted in the field in the above picture.  The lighter green rows in the picture were not inoculated at planting.

Those of you familiar with planting soybeans or other legumes are likely familiar with inoculants.  For purposes of this  discussion, we’ll skip most of the science behind how and why inoculants work, but if you are interested there are multiple pages online that go into as much detail as you could possibly want.  An example of a good, easy-to-read explanation of inoculants is here.  To make a short, oversimplified explanation; inoculant products contain rhizobia bacteria that form mutually beneficial relationships with leguminous plants (peanut, soybean, alfalfa, clover, etc) and allow for conversion of nitrogen in the atmosphere into ammonia nitrogen; a form that is usable by those plants.  This allows for growth of the crop with very little, or more commonly zero supplemental nitrogen.

For the purposes of this post, the first point to be made is that if you are considering using the same inoculant for peanut that you use for soybean, don’t do it!  Rhizobium strains in inoculant products are crop (or group of crop) specific.  The packaging of a a product intended for use in peanut will include a statement that the product is to be used specifically for peanut and should give an indication of the number of Bradyrhizobium sp. or Bradyrhizobium sp. (Vigna) bacteria that the product contains.  Conversely, inoculant products intended for use in soybean will include a statement that the product is to be used with soybean and should give an indication of the number of Bradyrhizobium japonicum bacteria that the product contains.  As you can see, if you are simply looking for the term ‘Bradyrhizobium’, it’s easy to get the products confused, but making that distinction could be the difference between inoculant success and failure.  To throw another wrench into the system, many of the inoculant companies today make special ‘additives’ to be used in combination with inoculants that are claimed to improve plant health, increase root growth, increase seed vigor, improve yield, make more money, etc., etc., etc.  Because I haven’t yet tested those products here in Mississippi I can’t speak to their effectiveness, but my word of caution is that these products are designed as additives and won’t do the job as a standalone product.  Although the packaging should say that the additive is designed to be used in conjunction with an inoculant, these products can still be confusing, making it easy to mistake them for the inoculants themselves.  This is where careful examination of the label comes in handy.  Again, true inoculant products should give an indication that there is some number of Bradyrhizobium sp. or Bradyrhizobium sp. (Vigna) in the formulation.  If you have any questions about whether or not you are using the correct product, don’t hesitate to give me a call.

Inoculants come in three basic formulations; liquid, granular, and sterile peat/powder.  Liquid products are becoming more and more popular and I highly recommend using them if you have in-furrow liquid application capabilities.  They generally contain the greatest number of bacteria.  Granular products are most commonly put out through a dry metering box (like an insecticide hopper) that places the product in the seed furrow.  These products can also be successful, especially if soils are dry at planting.  Sterile peat or powder is designed to be applied directly to the seed prior to the seed being placed in seed hoppers.  This often presents problems for numerous reasons.  First, it is difficult to evenly apply the product to seed.  If seed is dry at application, the product may not ‘stick’ to the seed well enough to provide optimum results.  Contact will be increased if seed is wetted, but you can imagine the mess that can be potentially made using that method, especially considering there’s a strong chance that the seed has already been treated with fungicide or fungicide + insecticide.  Also, because many growers are using bulk bags of seed when planting, the logistics just don’t allow for these type of treatments.  Having said all of that, use a liquid or granular product in the furrow to achieve best results.  If a liquid product is used, non-chlorinated water should be used as a carrier, as chlorine can potentially be lethal to the bacteria.  If a liquid or granular product is used, proper equipment calibration is also key.

No matter the formulation, keep in mind that these inoculant products contain 100’s of millions to billions of bacteria per gram of product.  These bacteria are living organisms.  Keep inoculants cool and dry and out of direct sunlight.  Rapid death of the bacteria can occur if packages are left in the back of a truck on a hot day, for example.  If using a liquid, only mix up as much product as you intend to use that day.  Most labels say that the mixed product is viable for 24 hours but the quicker it is used after opening and mixing, the better.  While not in operation, tanks containing the inoculant mixture should be placed in a shady area to avoid exposure to direct sunlight and elevated temperatures.  Most liquid inoculants are compatible with many fungicides and other products designed to be applied in-furrow.  Information about tank mix compatibility and time limits on exposure is readily available so consult the label or contact your sales rep or myself with any compatibility questions.

While important anywhere peanuts are grown, I think proper use of inoculants is going to be especially important here in Mississippi.  Any new ground or ground out of production for 4+ years should always receive an inoculant application.  It is often recommended that inoculant should also be used if peanut is being planted in fields that have had standing water or total saturation for extended periods.  This will likely be more common in parts of Mississippi than in the deep sands of the peanut belt, making inoculant application important for us.  Given the relatively low cost and the potential detrimental effects from not using them, I consider inoculants to be inexpensive insurance.

In a couple of weeks, I’ll post about what to look for when checking to make sure the rhizobia bacteria are ‘doing their job’.  As always, if you have any questions, concerns, or comments, don’t hesitate to call me at 859-317-3142.

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Brendan Zurweller, Extension Peanut Specialist, Mississippi State University
By Brendan Zurweller, Extension Peanut Specialist, Mississippi State University May 6, 2014 15:48
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