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The Inoculation Didn't Work - Why not?

We occasionally receive word from a customer that our inoculant failed to develop any infectivity on plant roots in trials, usually in nursery situations. When dealing with living organisms, it can be difficult to specifically determine why the fungi perform so well in one situation and not in another, but there are some "usual suspects" to consider.

Here are are the primary reasons why inoculations fail:

  1. Improper potting mixes. Easily the leading reason. The mycorrhizal fungi are adapted to earth-type soils, not to partially-composted wood. Even kitty litter or pure sand would be better for fungi than bark or sawdust-based media, some of which retain fungicidal qualities. A wood-products growing medium might work for chemistry-based growing methods, but is not a good choice for biology-based methods. This, of course, pertains to plants being propagated in nurseries. The blend of species in our products should be suited to nearly any in-ground planting situation, and we see fewer performance problems in fields.
  2. Over-fertilization and over-watering. Nurseries in particular are reluctant to change any of their traditional routines and often try to use our inoculants as "add-ons" to their regular chemistry-based procedures. The effects of the beneficial fungi will diminish as soil fertility (especially the presence of P) increases. The fungi perform best in low-fertility soil, at least what we humans consider low-fertility. In natural settings, plant nutrients come from decomposed leaf litter, bird droppings, and microbial conversion of mineral elements. Drenching seedlings with liquid fast-acting fertilizer can make the soil unsuited to biological elements. Actually, the most powerful biostimulant in the world is a "help!" signal to the fungi from the roots of a stressed plant. The fungi "go into a higher gear" when a plant's root exudates signal that it is stressed, either from lack of water, lack of some necessary nutrient, or pathogen attack. A nursery that puts inoculan spores in a proper low-fertility potting mix and then briefly withholds water from sprouted seedlings will see great results fairly quickly - but how many would dare do this?
  3. Incorrect species of fungi for the particular plant/soil situation. Some types of fungi will do well in a given environment while others will fail. Experimentation by the grower is the only real way to find the best inoculant to use in their particular soil. (We have 15 different types of Endo and Ecto fungi spores in our Landscape Inoculant, but a rare situation might need #16.)
  4. Inadequate application dosages. With eight types of AM fungi in our blends, a given dosage per crop plant might call for a minimum of 25-50 spores to ensure that at least a few of the right type are included in each dose. I know for a fact that many laboratory researchers apply as many as 500-1000 spores per plant when conducting their studies, which would be economically impossible for real-world growers to duplicate.
  5. Poor inoculant. Hopefully, never ours, but as more supplier companies enter the marketplace, there will predictably be a very wide range of quality between inoculants. I suggest a careful reading of the labels. What species are included - just the easy-to-propagate Glomus intraradices or several other types? (Multiple species improve the odds of infectivity.) What is the guaranteed spore count, and does the count refer to only Endo-types or is it inflated with inexpensive Ecto types? Is the specific word "spores" used, or do you see the word "propagules"? Endo spores are relatively expensive and very durable, while propagules are generally nothing more than shorter-lived hyphae fragments. (We do not even count the many thousands of hyphae pieces in our products.)

I could probably come up with more possibilities, but the above - individually or in some combination - are the most likely reason(s) why a grower might have problems getting the fungi to perform.

There can be a huge potential benefit in growing plants with the powerful mycorrhizal fungi on the root systems, both for nursery propagation and after outplanting. The nurseries, farmers, landscapers, and soil reclamation people who manage to figure out how to create hospitible soil environments for the fungi will be well rewarded. We'll do our best to help them.

Happy Holidays, my friends.

Don Chapman
President, BioOrganics, Inc.

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