Compatibility Of Soybean Fungicide Seed Treatments With Inoculants

Most soybean producers know that bacterial seed inoculants need to be handled with care to maintain viability of the living Rhizobia bacteria. This means keeping the product cool, moist, out of the sunlight and applying the product to the seed no more than four hours before planting.

An issue that always seems to be raised at winter crop production meetings is that of the compatibility of seed inoculant with seed fungicide treatments. The compatibility of inoculants with seed applied fungicide treatments is an important issue. Most all fungicide seed treatments will have a detrimental effect of the health of Rhizobia.

Some inoculant labels will list their compatibility with popular fungicide treatments. Compatibility rating categories may include: Compatible, Marginally Compatible, or Incompatible and may include results of in-field or lab testing. Only fully compatible treatment combinations should be considered.

John Gaska, UW Extension Soybean Outreach Specialist, recommends the following general rules for applying inoculants in conjunction with seed treatments:

  • Unless strong compatibility is indicated by the inoculant label, in-furrow application of inoculants will give the best result when seed treatments are used.
  • When inoculants and seed treatments are used together, keep the exposure time to a minimum.   Usually less than 4 hours is best.  Re-apply inoculant if the seed has been treated over 4 hours and not planted yet.
  • If the chemical seed treatment is a liquid, apply it first, allow it to dry, and then apply the inoculant.  Some inoculants are labeled to be tank mixed and applied at the same time as the seed treatment, but check label first for instructions.

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