Mycorrhizae Frequently Asked Questions

Can I apply too much inoculum?

No. You must apply enough inoculum so that the mycorrhizal fungus propagules will come into direct contact with roots that can be colonized.

What is the minimum amount of inoculum needed to form mycorrhizae?

Mycorrhizae can form from only one spore that germinates and infects a root, but it may take a long time for the fungus to spread to a significant portion of the root system. Therefore, it is better to initiate multiple infection sites to speed up the colonization process. The minimum needed depends on the size and age of the root system. In other words, there is no specific answer to the question.

How do mycorrhizae work?

Mycorrhizal fungi colonize roots forming a biological link between the root and the soil. The fungus grows into the root and out into the soil. The plant responds by altering its physiology in a number of ways. The fungus in the soil absorbs water and nutrients from the soil and conducts them back to the root. Formation of mycorrhizae affects the composition of the microorganisms around the roots, and some of those microbes can influence the plant growth and health.

If there are mycorrhizal fungi in the soil, why inoculate?

The mycorrhizal fungi in the soil my be relatively few and located some distance from new plant roots, thus delaying the formation of mycorrhizae for some time. That delay could be critical to the growth process and benefits from mycorrhizae. The sooner mycorrhizae form, the better for the plant.

Are some types of mycorrhizae better for some plants?

VA mycorrhizae exhibit relatively little host specificity, but some species or strains function better in certain soils than others, so the plant response can be greater. Therefore, fungi can be selected to best match the soil of application regarding soil pH, organic matter content, etc.

Can I apply pesticides with mycorrhizal fungi?

Pesticides applied to the foliage of plants generally do not have any adverse effects on mycorrhizae formation or function. Some fungicides applied to soil do inhibit mycorrhizae; soil fumigants can kill mycorrhizal fungi.

Do fertilizer applications affect mycorrhizae?

High rates of fertilizers, especially phosphorus, inhibit the formation of mycorrhizae; organic forms of fertilizers seems to have less inhibitory effect on mycorrhizae than inorganic, soluble fertilizers.

Do mycorrhizae stimulate root growth?

Generally, mycorrhizae stimulate plant growth, including root growth, due to improved plant nutrition.

Do mycorrhizae fix atmospheric nitrogen?

Mycorrhizal fungi themselves do not fix nitrogen, but bacteria that may associate with them can.

Do mycorrhizae control plant diseases?

Generally, mycorrhizae improve the health of plants and their roots, so diseases may cause less damage. Mycorrhizal plants are better able to resist infections by plant pathogens.

Are mycorrhizal fungi present in composts?

Mycorrhizal fungi are not present in composts unless the compost contained plant roots. If the compost has been heated from microbial activity, then the mycorrhizal fungi may have been killed.

Do composts affect mycorrhizae?

Some composts may be compatible with mycorrhizal fungi, but others may have high salt or nutrient content that can inhibit mycorrhizal fungi.

How long do mycorrhizal fungi survive in soil?

The spores of VA mycorrhizae are highly resistant and can live for many years in the absence of plant roots. When roots come near, they germinate and colonize the roots. Thus the shelf life of Agbio-Endos/Ectos can be years in some cases, but always at least two years.

Can mycorrhizal fungus inoculum be applied to established plants like trees, plants and vines with beneficial effects?

Mycorrhizal fungi must be brought in contact with infectable roots, so it is not likely that established plants can be inoculated. Furthermore, established plants probably have already acquired mycorrhizal fungi, and trying to add inoculum would not be effective. If plants are struggling to survive in the absence of mycorrhizae, then injection of inoculum or drenching liquid suspensions of inoculum into the root system may be helpful.

How fast do VA mycorrhizal fungi come back into soils that have been fumigated?

It could take a long time for fumigated soils to become recolonized with VA mycorrhizal fungi. Their spores are large and are not readily blown around in the air. However, they can be moved around in dust or soil movement, in water that carries soil, or can follow roots up into fumigated soil from below the fumigation level.

How can one know that inoculation with mycorrhizal fungi is needed?

Most all agricultural crop plants can form VA mycorrhizae, but some are much more dependent on them than others. Highly dependent plants will need to be inoculated if natural inoculum is not likely to be present in sufficient numbers, as when the soil has been fumigated to kill pathogens, weeds, or insects; or plants are grown in soilless media devoid of mycorrhizal inoculum. Highly disturbed sites like road cuts, mine sites, highly eroded or salinized soils, or soils that are very nutrient deficient or drought stressed should be inoculated or plants to be grown in them should be preinoculated.