Bio-stimulant is a loose term that includes microbial inoculums, energy sources for microbes, soil conditioners, plant hormones, and other non-nutritional growth-promoting substances. Products containing both bio stimulants and fertilizers have further muddled this definition, they tell you what they do, not what they are. Differentiating between fertilizer response and bio-stimulant response is difficult, if not impossible. No doubt this is precisely what the manufacturers of  such products have intended, a paraphrase that facilitates of mimic natural processes already occurring in trees and soils. Since the non-nutritional component alone may not elicit a plant response.

                One group of bio stimulants is plant hormones. These products may contain one or more of the following: cytokinins,  gibberellins, auxins,  abscisic acid, and ethylene. When growing under normal conditions, plants have adequate levels of hormones for normal growth and development. Physiological processes in plants involve an interaction of several hormones, and individual hormones have several functions. Many hormones have different functions in different plant species.    

                Normal hormone production can be influenced by environmental and cultural stress. Different species of trees,  growing in different environments and locations, with different stresses, at different times of the year are likely to react in different ways. One of these reactions will undoubtedly be with hormone regulation, and this is consistent with the variability in tree's response to hormone applications. There is no evidence to suggest that applications of plant hormones will yield favorable or consistent results with respect to improved plant health. Applying hormones to plants may produce an inhibitory or undesirable effect. Without research results to identify and quantify treatment regimes, it may be wise to avoid tampering with plant hormonal activity.  Testimonials and aggressive marketing practices have been the substitute for independent research results.           

                Another type of bio-stimulant available on the market contains humate or humic acid. These are naturally occurring organic compounds that are the end products of biological decomposition. They are extremely resistant to further decomposition.  Products containing humates claim to increase cation exchange capacity, increase microbial activity, and chelate micronutrients. Iron, copper, manganese, and zinc are rarely deficient in forest soils, but can be tied up due to soil pH. Supplementing micronutrient availability may only provide negligible benefits, however applying sulfur will help lower pH levels and increase nutrient solubility. Humates are the end result of decomposition and thus resistant to further breakdown, and do not stimulate increased microbial activity. Studies indicate humates and humic acids can reduce the efficacy of pesticides by reducing their absorption by plants and pathogens. However, studies  show that the fulvic acid component of humates can actually increase the solubility of pesticides and may increase mobility .

THE SOIL microbial consists of a wide array of organisms with numerous and many yet-to-be-understood complex interactions. Studies of soil microbiology have recently made considerable progress in furthering our understanding of microorganisms and their function in soils supporting tree growth.  Public opposition to the use of synthetic fertilizers and pesticides have prompted much of the recent research. While very useful findings have been obtained through research, these studies have yielded the realization that considerably more research will be necessary to develop solid recommendations for managing soil microbial populations. This article will review soil microbiology and discuss how to select and investigate the use of various products and management techniques. The intent is to provide information to arborist,  other tree managers and consumers, so they can objectively evaluate the plethora of products that claim to produce better tree health care by influencing soil microorganisms.

SOIL MICROBIOLOGY

A productive, biologically active soil can contain as many as 45 quadrillion microorganisms in the rhizophere or root zone of 1,000 square feet area around a tree. A single teaspoon of fertile soil already has few million soil based microbes. This population consists primarily of bacteria, actinomycetes, fungi, and algae. Within each of these groups of organisms are many diverse genera and species whose populations fluctuate widely both spatially and temporally. Among the factors contributing to this variation are energy sources, nutrients, oxygen, carbon, hydrogen, water availability, temperature, soil pH, atmosphere, and the genetics of the organism. The result is a very complex system influenced by a combination of biotic and abiotic functions. These specific function and characteristics of the constituents of the microbial community are not straight forward and are not thoroughly understood.

                Fungi are involved in organic matter decomposition, mycorrhizal associations, and tree diseases. Mycorrhizia  (root fungus) are known to improve nutrient and water uptake. In fact, mycorrhizal associations have been shown to provide inter-specific transfer of phosphorus and other nutrients. Endophytic fungi form associations with plants and discourage insect predation. Actinomycetes decompose organic matter, and are also capable of producing antibiotics that may confer disease-suppressive qualities.

                The bacteria populations in soils contribute a range of benefits to plant growth. These, include nutrient recycling, soil aggregation, solubilility of immobile elements, competition with pathogenic organisms, organic matter decomposition, and the production of  phytohormones. Bacteria populations and their associative functions are highly significant and diverse to plant productivity. Bacteria tend to utilize simple organic compounds, while fungi and actinomycetes are more proficient users of complex organic compounds.

                Much of this microbial activity occurs in the region of the soil, known as the rhizosphere. Within this region from the root area, microbial activity enhances nutrient cycling, the affect of soil pH, and nutrient availability. These symbiotic associations with soil based microbes, colonization of  microorganisms, their interactions with roots and pathogens and ionic mobility. Simply put, this is the dynamic interface between plants and soil where microbial function is in action.

                Trees  have a tremendous amount of rhizosphere due to their fibrous and extensive root systems, 95 % of the roots are within 12 to 16 inches from the surface and may extend three times beyond the drip line. Although our understanding of the organisms, and processes are increasing, there is still a lot more to be discovered to improve tree health. However, studies have used mineral nutrition to affect soil pH and control root-infecting pathogens. There are countless unsubstantiated product claims that purport to favorably affect rhizosphere processes. In the tree root systems, there is still a significant lack of university research to validate these claims.

                Most soils supporting tree growth contains a very active and diverse microbial population. Some people  have alleged that the use of synthetic petro-chemical fertilizers and pesticides reduces or eliminates the microbial activity by altering the soil pH or causing direct and indirect toxicity to organisms. Except for the presence of inert ingredients in some formulations of pesticides that have or may cause toxicity. One ongoing study indicate that pesticides do not adversely affect most non-target microorganisms.

                Due to the productivity of tree roots in forest settings, organic matter and microbial activity are rarely deficient. The one system that may limit microbial activity due to a lack of favorable habitat in urban construction settings, due to reduced nutrient- and water-holding capacity, due to soil compaction surface soil removal and replacement. Microbial populations generally will stabilize 3-5 years after establishment, so amendments to these soils can facilitate a more rapid colonization of the rhizosphere and should lend stability to the system. These amendments  would include various organic types, including composts and/or inorganic amendments. The re-establishing root zones could be due in part to the lack of sufficient microbial activity to buffer the system from environmental extremes and harmful pathogens.

SOIL MANAGEMENT                                                                                                                                  

The important role microorganisms play in plant and soil health is the difficulty of quantifying and qualifying that role. Molecular testing capabilities have enabled fairly accurate quantification of the microbial component in soils. This will not yield a clear understanding of the diverse function and interaction of the various organisms, it is a beginning point for assessing microbial health in soils. Keep in mind that microbial populations fluctuate widely across sites and throughout the seasons. Microbial testing may provide comparisons of soil that supports healthy or struggling trees. Be sure to account for other factors that may be limiting growth, such as sunlight, air circulation, drainage, fertility, traffic flow, landscape structures, soil compaction, and drought conditions. Soil testing for microbes may help assess whether microbial activity is influencing soil quality.

 MICROBIAL INOCULANTS                                                                                                                                                  

                Microbial inoculants have been formulated for deep root injection for trees, with claims of accelerated organic matter decomposition, improved nutrient use efficiency and availability, soil conditioning, disease control, mycorrhizal associations, and others. The success of these inoculants has been limited for a number of reasons. Be aware that the microbial community is a very diverse and complex of organisms. Natural competition, antagonism, and predation limits the successful establishment of introduced species. If the organisms can be kept alive until application, many are sensitive to UV light and must be applied frequently to establish sufficient populations. Finally, some companies will not even list what organisms they have formulated, because they are proprietary. Without knowing what is being applied, it is impossible to gauge the potential benefits. These organisms could be detrimental to your soils by competing with the beneficial soil based organisms already present in your soil !  Injecting organisms through irrigation systems has not as yet proven as an effective and consistent method of microorganism application. Population interactions within the soil are dynamic and interrelated, introduced organisms are slow to colonize habitat and generally fail to persist. Also it is unclear whether the introduction of microbes in the soils will produce a lasting change and will be beneficial in the long run.

COMPOSTS                                                                                                                                                                                                                         With little doubt, the most promising method of managing and enhancing the activity of soil microbes is with composted organic matter in wastes and other materials. Ironically, this is one of the oldest agricultural practices. Composts have been shown to add an active microbial component to soils and to stimulate those microbes already present in the soil. Well-decomposed organic matter provides excellent habitat and energy sources for soil microbes, beneficial insects and will provide more permanent benefit than inoculation with microorganisms. Composts will effectively enhance soil aggregation, provide nutrients, reduce compaction, and improve soil porosity. Soils amended with compost will exhibit greater nutrient- and water-holding capacity and can offer improved establishment and disease control. The use of composts management presents a viable means of recycling municipal and industrial wastes while improving soil quality. Composts vary considerably, depending on their source. Commonly used composts include yard wastes, poultry litter, animal manure, municipal wastes, and food wastes. It is recommended to have composts tested for organic matter content, moisture content, pH, nutrients, metals, and soluble salts.

BIOLOGICAL PEST CONTROL

                Biological control operates on basic interactions with the soil community, e.g.. competition, antagonism, predation, parasitism, and pathogenicity. Exploiting these interactions include microbial inoculants and organic amendments. While numerous organisms with potential as inoculants for disease control have been studied, few have demonstrated any efficacy or real effectiveness. Biological control of insects has been somewhat successful in recent years with such organisms as nematodes, soil bacteria and fungi, although registered products are some what limited.

                Shortcomings exist in the understanding pest control mechanisms, relationships with other organisms in the community, formulation and delivery methods. Foliar disease control with inoculants is limited due to UV sensitivity of the organisms. The difficulty in delivering organisms to the roots has preempted much success in controlling root diseases. Because successful pest control typically depends on the establishment of high population levels, frequent applications become necessary. Organic soil amendments and additives, particularly compost, have perhaps a greater potential for effective biological control of diseases than inoculants. Well-composted material (2-3 years) often exhibits disease-suppressive characteristics. University studies have demonstrated significant and lasting disease suppression root rot when composts were used as amendments. Continued research in this area to reveal the microbiological mysteries should help develop more reliable and predictable composts for disease suppression and soil conditioning. As alluded to earlier, proper composting techniques and laboratory testing coupled with on-site testing will reveal what to expect from composts.  

NEW PRODUCTS

Financial responsibility and sound management dictate that product purchasing decisions are of the utmost importance. Never before has the tree industry had as many commercially available products for use. So how does one choose between the good, the bad, and the ugly or the tree goop?

                There are products that have been registered with the EPA and can legally justify the claims of the product. The first place to start is with the product label. These are products that contain active ingredients. There are unregistered products marketed for various uses, some of which are supported by independent research. Then there are products marketed for various uses without supportive research. These products use testimonials and aggressive marketing to make a sale, and often can be classified as snake oils or tree goops. Let's be sure we understand the independent, scientific research that supports product use. Be sure you know who conducted the research, where, under what conditions, and the relevancy to trees and soils. Also, look for replication in the study, good comparative treatments, and least significant differences. Check closely to see that the results have been duplicated at another site by another independent  researcher, and Universities and that results have been published in a refereed journal. Make no mistake, slick brochures and displays can be confusing! One product advertisement claimed the product would restore and extend the useful life trees, eliminates disease, increased and boosted the metabolism among other things. This companies needs scientific counsel as much as legal counsel. Finally, call the University extension personnel and researchers and ask technical representatives what the active ingredients are and what are their modes of action.

                If a product you are interested in passes this initial screening, it is strongly recommended to conduct on-site testing for your trees. Many of these products are not cheap, and good management involves an economic analysis. Test the material at several locations on trees representative of different conditions, replicate and use untreated controls and other treatments in side-by-side comparisons. All too often, new products are tried without a control. It is impossible to determine what effect, if any, the new product has. Take consistent, monthly ratings of your test sites for leaf color, canopy growth roots and disease control and note stress tolerance differences. Good tests require at least two years of field data. Because a product sounds good and will cause no harm is not reason to use it, and such a decision is representative of poor management.

CONCLUSION                                                                                                                                                                         

                Tree Health Care management is a continually evolving science, and as our understanding of the microbial community in soil systems improves, new products will routinely hit the market. Some of these products will be useful, and others will not. Independent research will be essential to the development of effective products. Companies marketing biological products would be wiser to fund some research than to purchase full-page ads in   popular trade magazines, if they have faith in their products and insure that the product is backed by bonafide University research !

                If organic management is ever completely realized, it will certainly be through a gradual phase-out of synthetic products. With the advent of biological products, Tree Health Care Service and Arborists must also keep themselves apprised of advances in synthetic chemistry. Many new products have been developed from synthesized organic compounds that are effective at very low levels of active ingredients, have low water solubility, and a strong binding potential with soil and organic matter. New synthetic chemistries are better for the environment than many of the older chemistries.

                The importance of a strong microbial community cannot be questioned. The effectiveness of various products available to stimulate microbial activity can be questioned. Become familiar with soil microbiology and processes, check for duplicated independent research to support product claims, and test the material yourself to be sure it is effective and makes good economic sense. But whatever you do, don't forget the basic rules of  successful tree health care, proper diagnosis, safe pruning practices, proper fertility, disease control and good water management.

MISSION

The intent of this article and previous articles relating to “TreeLife”,  the first of the series  “The New  Cure For Oak Wilt” is to provide reliable information, for the consumer and report the results of studies and research demonstrating the effectiveness of  Bio-Stimulants and Soil Inoculants. These are the few companies which are spin offs from Bio-Save - Fredericksburg, TreeLife - Marble Falls, New Growth Tree Service - Pipe Creek , and the newest  “Live Oak Technologies” of  Burnet.  All, whom, aggressively sell these types of products as Oak Wilt Treatments and as an Organic Solution for tree health and as a cure for Oak Wilt.  These treatments are very expensive when you consider their effectiveness or lack thereof and remember you are paying a very high price for the additives of fertilizer (NPK) and water.

“Diseases are created when we destroy the harmony reigning among  mineral substances present in infinitesimal amounts in air, water, food and most crucially soil”.

Dr Alex Carrel, “Nobel Prize”  winning Scientist

We must encourage growth without destroying balance;  We must preserve balance without  impairing growth.

W. R. Dixon