Mycorrhizae and Biofungicide survival in packaged media

Mycorrhizae and Biofungicide are bio-additives that are available premixed in different PRO-MIX® formulations such as PRO-MIX® BRK, BRK20, BX, HP, LP15, etc. The advantage of having these bio-additives premixed in the growing medium is the convenience of not having to add them at all during the crop cycle and they benefit the crop throughout the growing season – there is no need to reapply these biological organisms. Our biologically amended PRO-MIX® products are easy to use and most storage conditions are compatible with the biologicals. In this article, we will address questions that come up regarding the integrity of these organisms.

Both groups of organisms occur naturally in soils. They have been selected through a screening process for their growth-enhancing properties or disease suppression. Their modes of action are slightly different. Mycorrhizae is a fungal biostimulant that colonizes the roots, extending the root surface area to acquire water and nutrients where the plant roots are not present. For its part, biofungicide is a rapid colonizing bacterium that reduces the occurrence of plant root diseases and that can also enhance plant growth.

Mycorrhizae: Mycorrhizae is defined as a symbiosis between plant roots and a fungus, which mutually benefit each other. This symbiosis, known as the "Arbuscular Mycorrhizae type", is most common among vegetable and annual plants grown in greenhouses. In non-farmed environments, mycorrhizae colonize almost 70% of the plant species present. These types of mycorrhizae do not occur naturally in peat moss and growing media; therefore, they are introduced into growing media.

Mycorrhizae not only colonizes plants in PRO-MIX®, but continues to colonize plant roots even after transplanting in soil. It will survive almost all temperature extremes and climatic changes from freezing to intense heat because they have very resistant cells, called vesicles of spores, which are filled with lipids. These spores can be compared to seeds of plants because they allow for long survival in the soil. When mycorrhizae is added to growing media, the storage temperature changes are similar to those in soils. When storage temperatures become cold in winter, mycorrhizae gradually prepare their cell walls for freezing temperatures so they can survive. Even high soil temperatures do not kill mycorrhizae. Carpio et al, at Texas A & M University, conducted tests on various stresses in Texas nurseries during summer heat, and mycorrhizae remained functional in plant roots even at very high summer temperatures.

The Mycorrhizae™ Premier Tech added to PRO-MIX® growing media are viable up to 2 years in storage, which includes exposure to freezing temperatures. However, when mycorrhizae are sold only as inoculants, there is a narrow storage temperature range because the mineral carriers used in inoculants do not insulate as well as peat moss. The table below highlights some of the key differences between both types of products containing mycorrhizae.

Biofungicide: Premier Tech Horticulture currently offers two biofungicide bacteria: Bacillus subtilis in our PRO-MIX® Biofungicide product line and Bacillus pumilus in our PRO-MIX® Biofungicide + Mycorrhizae product line. Both have the same tolerance to storage temperatures. These biofungicides have been selected to help suppress root diseases caused by Fusarium, Pythium and Rhizoctonia. Many tests confirm these biofungicide stains can survive in prolonged storage temperatures up to 120oF and well below freezing. There is abundant research data that shows these bacteria can survive long periods of time at various temperatures.

Most other biofungicides available on the market utilize different types of microorganisms. They work well for root disease suppression and biostimulation, but are more susceptible to viability loss from heat and frost because they do not have the hearty, spore-like structures the Bacillus bacteria have. The manufacturers of these products also recommend shorter storage periods in growing media.

Premier Tech Horticulture recommends using its PRO-MIX® peat-based growing media within 9-12 months of manufacturing and its peat/bark-based growing media within 6 months of manufacturing. This is mainly due to the natural biodegradation of the wetting agent added, which helps with the wetting of peat moss. Once the shelf-life has been reached, the growing medium may have difficulty absorbing water. For more information on this subject, please consult your Premier Tech Horticulture’s Grower Services Representative.

For more information:
Premier Tech
T: + 1 800 424-2554 (Grower Services)
T: + 1 855 867-5407 (Sales)

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