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
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.
and aggressive marketing practices have been the substitute for independent
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 .
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
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.
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
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
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.
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.
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 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.
With little doubt,
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.
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?
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
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.
a product sounds good and will cause no harm is not reason to use it, and such
a decision is representative of poor management.
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 !
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.
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.
The intent of
this article and previous articles relating to TreeLife, the first of the series
The New Cure For Oak
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
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
encourage growth without destroying balance;
We must preserve balance without
W. R. Dixon