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Endomycorrhizal Benefits for Professional Growers and Horticulturists

Endomycorrhizal fungi (also known as arbuscular mycorrhizal fungi, or AMF) are beneficial microscopic organisms that live in the soil and have evolved a symbiotic relationship with approximately 85% of the world’s plant species over the past several hundred million years.  These fungi predate the evolution of terrestrial plants, and it was the partnership with mycorrhizal fungi that allowed plants to begin to colonize dry land and create life on Earth as we know it.

How does this relationship between beneficial fungus and plants work?

The AMF symbiotic relationship centers on the plant’s ability to produce carbohydrates through photosynthesis and share some of these sugars with the fungus in return for otherwise unavailable water and nutrients that are sourced from the soil or growing media by the extensive network of mycelial hyphae produced by the fungus.  It’s a two-way relationship of sharing resources between two species, thus a classic symbiotic mutualism.  The endomycorrhizal fungi rely on the plant, and the plant’s performance and survival are enhanced by the fungus.

How is this symbiotic relationship established?

Endomycorrhizal fungi can colonize plants from three main sources of inoculum: spores, colonized root fragments, and vegetative hyphae.  Collectively, these inoculants are called “propagules,” and this is the standard unit of measure that is listed on most commercially available mycorrhizal products.

To colonize plant roots, these propagules must be present in the substrate and in close proximity to actively growing roots of a compatible plant.  The growing root tips emit root exudates as they push through the substrate, which signal the fungi to colonize the roots and establish the symbiosis.  Once the roots are colonized, then the process is self-sustaining as the vegetative bodies of the AMF ( the fungal mycelium) continue to grow with the plant’s root system and additional spores and hyphae are produced.

To inoculate plants grown professionally or in a home garden, AMF propagules can be incorporated into the substrate prior to or during planting or they can be top-dressed on the surface and watered into a porous substrate.  They can also be applied as a dip or slurry at the time of sticking a cutting, seeding, or at the time of transplanting.  The propagules can also be applied as a drench to the soil and watered-in, applied to the outer surface of the rootball before transplanting, or used in transplant hole and backfill soil.

How can professional growers utilize this symbiosis?

The application rates for endomycorrhizal fungi are based upon the number of propagules per volume of soil for container-grown plants and per area of coverage for turf and landscape plantings.  Therefore, large containers will require more propagules than smaller containers.  For a professional grower, it is more cost-effective to treat plants early in the crop cycle when they are growing in smaller volumes of soil, and will require fewer propagules per plant to achieve colonization.  Germination of the spores occurs relatively quickly after contact with growing roots, but full colonization of the roots can take several weeks.  Plants will reap the full benefits of the colonization within 6-8 weeks after application.  Some plant species will demonstrate the benefits of mycorrhizal colonization sooner than others.

The mycorrhizal fungi colonize the developing roots by growing into the plant’s root cells to obtain carbohydrates and simple sugars (food).  The tiny fungal mycelial threads grow throughout the available soil volume and effectively “mine” the soil for water and nutrients that the plant cannot access or absorb on its own.  The enhanced water uptake helps the plant to resist drought conditions and ensures faster plant response if its roots are damaged by adverse conditions (drought, water-logged conditions, high salts or high soil temperatures).  The mycelium also secretes organic compounds that help solubilize nitrogen, phosphorus and other macro- and micronutrients from the substrate.  These nutrients are actively transported by the fungus to the plant to produce proteins and other components needed for vigorous growth and development.

How it Works Diagram

Why do horticulturists and professional growers need mycorrhizal fungi?

With traditional input-intensive growing protocols, nursery or greenhouse grown plants are produced under optimum conditions and may be able to perform sufficiently in the short-term, without the assistance from mycorrhizal fungi.  However, water restrictions in production and landscapes will encourage growers and consumers to be water-wise and utilize mycorrhizae as part of our water management programs and promotions.  Trials have demonstrated that the use of mycorrhizae can reduce water requirements significantly by increasing the plant’s ability to utilize and store water through the AMF mycelial network of hyphae.  Consequently, retailers and growers have realized reduce shrinkage due to drought and stressful conditions in the retail chain.

There is additional pressure to reduce the runoff of nutrients, especially nitrogen and phosphorus, from nurseries, greenhouses, and landscapes.  Both of these essential plant nutrients are accessed and delivered to the plants by mycorrhizal fungi, and in many instances these inputs can be reduced significantly by utilizing AMF without a noticeable reduction in crop time, appearance, or performance.

Excess water usage results in more runoff and excess fertilization results in more pollution of the environment.  Many conscientious growers welcome beneficial biological solutions like mycorrhizal fungi to help reduce these environmentally harmful growing techniques, and this type of technology is becoming a major part of the toolkit to increase the overall environmental sustainability of the horticulture industry in the long run.

Are professional endomycorrhizal products available for greenhouse and nursery growers?

Mycorrhizal Applications, the leading producer of mycorrhizal propagules in the US, produces a suite of professional products that make it easy for growers to trial mycorrhizae and to incorporate it into their production programs.  Their flagship “MycoApply” endomycorrhizal inoculum products contain four different Glomus species of AMF for optimal diversity and performance under most growing conditions and crops.  These flagship endomycorrhizal inoculant products are MycoApply Endo and MycoApply Ultrafine Endo.  MycoApply Endo is a granular formulation containing 60,000 AMF propagules per pound and is ideal for soil incorporation, as the granular consistency blends evenly with growing media and soils.  MycoApply Ultrafine Endo is a suspendable powder containing 130,000 AMF propagules per pound which can be soil-incorporated or prepared as a liquid suspension for use as a soil drench or plug tray dip.  Whether incorporating the granular product into your media or drenching with the suspendable powder formulation, it is important to get the propagules in the root zone as soon as possible and as early in the crop cycle as possible.

 

MycoApply Endo & MycoApply Ultrafine Endo

Where can I learn more?

Plants and mycorrhizal fungi have had a long-term relationship for over 400 million years and we are just beginning to understand this relationship better and are now employing this symbiotic mutualism in professional horticulture.  You can learn more about mycorrhizae by going to Mycorrhizal Applications’ website (http://mycorrhizae.com/) or by contacting Mycorrhizal Applications directly at 1 (866) 476-7800.  Resources and literature such as Fungicide Interactions with Mycorrhizal Fungi, and the Mycorrhizal Status of Plant Families and Genera are available through their website or by contacting them directly, in order to help you determine how to include mycorrhizal fungi most effectively into your professional growing protocols.  MycoApply products are also available through many horticultural distributors throughout North America.

Hugh A. Poole, Ph. D.

Horticultural Technical Consultant

September 12, 2017

©2017 Mycorrhizal Applications LLC.  All rights reserved.


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Managing Mites in Professional Greenhouses

We’ve all been there… You are growing your plants in your greenhouse and everything is going great, until it isn’t. The leaves are yellowing or browning, the new growth looks stunted or cupped, and old leaves are even falling off, or perhaps you see strange growths or galls on the plants, but you don’t see any obvious pests. It is possible it is a disease, but first let’s pull out the microscope and take a closer look. You might just have mites. Broad mites, spider mites, and eriophyid mites are all common mite pests that can cause these mysterious symptoms.

How do you know for sure if you have one of these types of mites?

Pull off a few leaves, both old leaves and newer leaves that look damaged or infested, and examine them under a microscope at 10x, 40x or more, depending on how good your eyesight is. Focus on the undersides of leaves when looking for mites and their eggs.

For broad mites specifically, you need to find some eggs, which are about 0.08 mm long and covered in tiny polka dots. The closer you can zoom in, the easier they are to identify. Adult broad mites are a translucent light-green to yellowish color, and the females have a white stripe down their backs. However, the eggs are really the most obvious identifier, with that tell-tale polka dot pattern.

Broad Mite Egg Photo

(Picture from Texas Plant Disease and Diagnostics Lab website.)

Spider mites are most easily identifiable by noticing the webbing along with the mites. Adult spider mites have two red eye spots near the head and females two dark splotches, one on each side of the body, and bristly bodies and legs. The eggs are small, clear and spherical.

Spider Mite Photo

(Picture from UC Statewide IPM Project,
Copyright 2001 Regents, University of California)

Eriophyid mites are elongate and have two pairs of front legs that drag the rest of the body behind it. They can be extremely small with the smallest being around 1/100th of an inch long so that field identification is virtually impossible. They often form galls on the plants and evidence of infestation is often determined by identifying the plant damage rather than trying to see the mite itself. Also note, if these mites are currently inside a gall then pyrethrins and pyrethroids won’t affect them. They are protected inside the gall and only susceptible to non-systemic insecticides like pyrethrins when they are out and about.

Eriophyid Mite Photo

(Picture from The Ohio State University website. http://bygl.osu.edu/node/751)

If you determine that you do have mite pests, then what?

Well, there are several options. If you are able to dispose of the infested plants, that can help cut down the overall population quickly, but you still need to manage the mites that are left, and luckily there are several good options. You can use horticultural soaps or oils, or other pesticide options labelled for mites. If you choose to use pesticides, PyGanic Specialty organically derived pyrethrins or EverGreen Pro 60-6 from MGK are good options to crush the mite population initially.  These botanically-derived insecticides have a very short residual persistence, so just a few days after application, you can then introduce beneficial predatory mites into your greenhouse to keep the destructive mites from returning in force.

PyGanic Specialty is OMRI listed, it contains pyrethrins, and can be used in certified organic facilities. EverGreen Pro 60-6 is not OMRI listed. It contains PBO in addition to pyrethrins which is a synthetically produced synergist. A synergist enhances the efficacy of the active ingredient, but is not itself an insecticide. Both products are in group 3A (pyrethroids/pyrethrins) of the insecticide resistance action committee (IRAC) classification system. They are sodium channel modulators.

To reduce the risk of contributing to insecticide/miticide resistance, growers must rotate modes of action in their insecticide applications. The Insecticide Resistance Action Committee (IRAC) has classified the modes of action into groups. Some other common groups of insecticides are group 4A (neonicotinoids), group 1A (carbamates), group 5 (spinosyns), and group 6 (avermectins). Something to take note of if you rotate with a group 4A neonicotinoid is that imidacloprid is known to cause outbreaks of spider mites, and other neonicotinoids may have the same effect so they may not be the best choice for a mite application. For all of these groups and the individual insecticides in them, they will have varying levels of residual activity, and other properties that may affect pre-harvest intervals, beneficial insects/mites, use sites and a host of other factors. In addition to the properties of the active ingredient itself, the formulation also plays a big role in residual activity, use sites, etc. so make sure to read the labels thoroughly on any product you use. You can check out the IRAC website to learn more about insecticide groups and rotation of modes of action to reduce the risk of resistance http://www.irac-online.org/modes-of-action/.

One of the benefits of pyrethrins over other active ingredients is the lack of residual persistence, which means they can be applied close to or even after harvest, and the ability to reintroduce beneficials soon after application without worry. Keep this in mind when deciding whether to use EverGreen Pro 60-6 or PyGanic Specialty vs another product with a different active ingredient. There are certainly times you may want a longer residual and a different mode of action. Evergreen Pro 60-6 and PyGanic Specialty aren’t always going to be the best options, but they do have some specific times where they fit in well.

PyGanic Specialty & EverGreen Pro 60-6

If you decide to utilize insecticides like PyGanic or EverGreen Pro, there are a few key points to take note of: The half-life in direct sunlight is about 11 hours. Therefore, spraying in the evening hours is recommended to prolong efficacy. Pyrethrins are also a broad spectrum insecticide so spray when pollinators are least likely to contact the sprayed area, again evening is probably a good time in this respect also.  These products will be most effective at the early stages of infestation or to knockdown large infestations that may have gotten out of control. When applying the insecticide for the initial knockdown, good coverage is the key. Make sure all the surfaces are thoroughly covered, and try to get the solution into those hard to reach areas like the buds. (Keep in mind that if you have beneficial mites in the greenhouse, pesticides or other product applications could hurt those populations too and predatory mites may have to be reintroduced into the system after insecticide treatments.)  Then, once the population has been knocked down, the introduction of beneficial mites a few days after the botanical pyrethrins will be most effective, now that the pest population has been brought down to a low to moderate level.

How can these insecticides be applied?

There are several pieces of equipment that work well. You can use a hand held manual pump sprayer, a backpack sprayer, a cold fogger, and even some types of irrigation systems. Check the label to determine which irrigation systems are okay to apply these products with. I also want to emphasize here that coverage of the plant when spraying is key. Make sure to thoroughly spray both the top and bottom surfaces of leaves.

How can I keep the mites from coming back, once the infestation has been resolved?

Mites can also hitchhike from plant-to-plant on flying insects such as whiteflies, travel on air currents, or even be transported by clothing or equipment. So if you have whitefly problems or other potential transport methods for mites, make sure the mites aren’t spreading to other areas. Mites can also hitch a ride on people or even strong air currents. Monitor healthy plants to make sure they aren’t getting new infestations that will have to be controlled too. It would also be wise to check for mites in any nearby weeds that could harbor them, as well as closely inspecting any incoming plants for mites to prevent reintroduction into the greenhouse. Treatment is always easier when you can catch the problem early, and of course, prevention of infestations altogether is always ideal whenever possible.

No matter which treatment method you use, it is important to continue to monitor new growth closely to make sure your plants are growing normally and not stunted. Remember to monitor both healthy looking and damaged plants, as scheduled monitoring of both the pest and beneficial mite populations is critical, along with good hygiene and sanitation.

Sandra Sleezer

MGK – Technical Service Coordinator

September 14, 2017


Back to Our Roots

  • Scientists, and now farmers are using beneficial mycorrhizal inoculants that will change the way you think about growing crops.
  • Learn what mycorrhizal fungi do and where they occur.
  • Unlock the power of mycorrhizal fungi for improved plant performance and yield.
  • Science helping your crops grow better, naturally.

 


What are Mycorrhizal Fungi video

What are Mycorrhizal Fungi

This brief animation shows how mycorrhizae work and how mycorrhizal fungi attach to roots, explore the soil and absorb vital nutrients for plants.