Green house pest management can be an overwhelming problem; especially in an aquaponic system. I posted this in my other blog Chicoaquaponic.blogspot.com. But these fungi are not limited to soil less gardens or greenhouses.
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I'd like to thank Forestry Images for thier wonderfully helpful site.
With great photos to help identify various problems, microscopic slides and petri dish samples they have made identification much simpler.
GH (Green House) pest management has three strategies, and which is best is really open for debate.
1- intentionally low pest security, meaning wide open large screens for
honey bees, pests, and pest predators. This works pretty good for lazy
folks like myself, especially if you are planting beneficial plants to
attract the predators. No fuss about pollination, and no big concern
about sterilizing everything.
2- moderate pest security. This one is fine for new greenhouses, and
light traffic GH's with cleanly guests. Once a pest gets inside, though,
trouble trouble.
3- high security, meaning positive pressure and HEPA filters, thrips
screening, humidity and temp control, haz-mat suits and dissinfect
routines. Just the thought of all that work spoils my mood, but is
probably the smartest long term plan for commercial use.
I'm a low security type guy. Address the pest directly. Mold? Increase
airflow and temp, decrease humidity. Spider mites, fungus gnats, white
flies, aphids? Allow predators, spray with tea, nuke them with CO2.
Nasturtiums are awesome for the garden by the way; trap crop or aphids,
pest predator magnets, repel white fly and spider mites. Yep. And
borage, and multicropping.
You can use the 'ol 3-5% oil + 0.5% dish washing detergent
remedy...works well but you have to be real careful to get as little of
the concoction into your system and take measure to cover up your FT to
protect from overspray. And even this low % of oil will burn pepper
plants if you have any...won't damage them beyond repair or anything,
just don't be freaked out by the necrotic lesions that will be left on
their leaves. peppers seem especially sensitive to this type of
treatment.
A better/easier/more fish safe bet might be a
naturally occurring fungus called Beauvaria bassiana that will take care
of a whole host of common garden pests...spider mites included (and
then some). B. bassiana can be purchased under the trade names
Botaniguard, Naturalis-L or Mycotrol-O the later two being ok'd by
OMRI...and more importantly it is fish safe (unlike any kind of oils or
most soaps).
Whatever you spray with make sure to repeat after 3 or 4
days...then again after 3 or 4 days...and then once more...since most of
these sprays wont kill the eggs that they've laid...so make sure you
get the bastards that have hatched...and spray the under-sides of the
leaves...Good luck. Spider mites are a royal PITA.
First I want to say Paul Holowko is one of my favorites. Check out his other videos.
In
this video Paul demonstrates how to grow your own oyster mushrooms. It
takes a while, but what fun especially if you have kids!
This is really interesting stuff! Most of what I have written was
learned from reading Teaming with Microbes by Lowenfels & Lewis. It
began as notes I was taking as I read the book. I think the book is a
masterpiece.
<<<==================>>>
The Soil Web
Plants secrete chemicals made of
proteins and carbohydrates, called exudate through their
roots.
The dark spots are bacteria. The less defined areas are the excudates emanating from the root on the right
Rhizoshere
The excudates are soluble sugars, amino acids and other compounds secreted by roots. They attract specific beneficial bacteria and fungi
in the rhizoshere which looks like jam under a microscope.
Bacteria, fungi, nematodes, and protozoa and even some larger
organisms compete for the excudates, water, and minerals within
the rhizoshere.
Nutrients which would otherwise wash out of the soil are
retained by these organisms which cling to the rhizoshere. .
Both good, and bad bacteria compete for the excudates, but if
the soil is healthy good organisms such as fungi that produce
inhibitory compounds such as penicillin and streptomycin
prevent disease from entering the plant. Also Mycorrhizal
fungi will be present to protect the roots, and deliver water,
phosphorus, and other nutrients.
Nitrogen is a basic building block of amino acids.
In general perennial trees and shrubs prefer fungal dominated
soil while annuals, grasses and vegetables prefer bacteria
based soils.
The key is to encourage the type of soil (fugal or bacteria)
to thrive so that the plants get the type of nitrogen they
they prefer.
It has become common practice to add "-icides" which are an
irritant to the worms. These poisons kill, or drive the worms away. On top of that, the common practice of adding salt based chemical fertilizers
rather than replacing organic material deprive the worms of
food, and tilling crushes, and kills any worms and arthropods
that might remain. The soil now lacks life, and becomes
compacted. Water no longer brings oxygen down into the soil,
and pathogens establish themselves.
Healthy soil will contain between 20 to 30 thousand different
species in just one teaspoon of good soil. Each group must be
kept in balance. Nature does a good job of this but
agricultural chemicals can kill off entire groups and decimate
the balance, which in turn removes food supplies for other
groups.
Jeff Lowenfels Soil Food Web Lecture
Letters are used to describe the soil layers The 'O' layer lies above the 'A'
layer. Several other horizons
lie below until bedrock is reached, but 'O and 'A' are the only two
layers gardeners are concerned with. . The 'O' horizon is
broken down further into 'Oi', 'Oe' and 'Oa' depending on the condition of decomposition the organic mater is in . The specific plant
source of organic material can still be identified in 'Oi' . In
'Oe' the organic material can only be identified as plant, and
finally 'Oa' has decomposed so much that identification is not
possible.
The roots grow in the rich humus of the A layer which is full
of organic matter, and biological activity which has leached
down into it from the 'O' layer above. It's important that
these layers have a good mixture of air, water, minerals and
organic matter. Humus or humified organic matter is complex organic compounds that remain after many
organisms have used and transformed the original material. Humus is not readily
decomposed because it is either physically protected inside of aggregates or
chemically too complex to be used by most organisms. Humus is important in
binding tiny soil aggregates, and improves water and nutrient holding capacity.
Minerals can influence the color of soil. Red
and yellowish tints are an indication of iron, purple - black
indicates manganese. Gray can indicate a lack of organic
matter, and an anaerobic condition due to the microbes having
converted the iron to Fe2+. Organic matter
produces much stronger coloring agents as it decomposes, but in an anaerobic soil it can also provide food for anaerobic bacteria that reduce iron
and manganese. Therefore gardeners are looking for dark soils the color of
coffee.
There are three categories of soil texture: The categories are
a description of how the particles sizes feel to your touch,
not the actual mater. Sand which is gritty, silt which is
like flour and clay is slippery. An ideal garden soil texture
will have all three in approximately equal amounts. This is
called loam. Loam has the ability to drain and draw air down
into the soil like sand while holding water and nutrients like
clay and silt.
An ideal ratio would be about 30 to 50% sand, 30 to 50%
silt, 20 to 30% clay and 5 to 10% organic material. You can
easily test you own soil by adding a tablespoon of water
softener to 2 cups of water and a sample of your soil. Shake
and let stand for 24 hours then compare the stratification.
Sand will settle to the bottom, silt will form the next layer
and then clay will finally settle leaving the organic mater to
float for a while at the top. With this knowledge you will be
able to adjust your soil as required.
Nematodes
may be useful indicators of soil quality because of their tremendous diversity
and their participation in many functions at different levels of the soil food
web. Several researchers have proposed approaches to assessing the status of
soil quality by counting the number of nematodes in different families or
trophic groups.* In addition to their diversity, nematodes may be useful
indicators because their populations are relatively stable in response to
changes in moisture and temperature (in contrast to bacteria), yet nematode
populations respond to land management changes in predictable ways. Because they
are quite small and live in water films, changes in nematode populations reflect
changes in soil microenvironments.
Nematodes
Polysaccharides produced by worms, fungus, and bacteria stick
the aggregates of the soil together, and make it easier for
the soil to hold capillary water and soluble nutrients. This
is the type of soil that will support soil biology, giving it
the ability to withstand floods, drought, freezing and animal
traffic.
Small particles of clay and humus carry positive electrical
charges call ions. Positive ions are called cations and
negative charges are called anions. The positive ion (cations) - pronounced as 'CAT Ion'
of humus and clay attract the negative ions (anions) of
calcium (Ca++), potassium (K+), sodium (Na+), magnesium
(mg++), iron (Fe+), ammonium (NH4+), and hydrogen (H+) so strongly that very little remains in solution. The nutrients are held in clay and humus where roots exchange (H+) cation for a nutrient cation.
There are also anions of chloride (Cl-), nitrate (NO3-),
sulfate (SO4-) and phosphate (PO4-) in the soil as well.
Since these are repelled by the humus and clay cations they
are easily leached away.
Plant root hairs also have cations which are exchanged for the
cations in the clay and humus. The root hairs exchange one
(H+) for every nutrient cation absorbed. This occurs at the
cation exchange site. The Cation Exchange Capacity (CEC) is a
measurement of how many exchange sites there are in the soil.
Higher CEC measurements indicate that the soil can store large
amounts of nutrients, which is why gardeners like a high
CEC. But the clay and humus which give the soil this quality
also prevents good drainage and aeration so a mixture with
good soil texture is important.
Each cation exchange, as well as some fungal and bacterial
exchanges effect the pH of the soil. Knowing the pH is
important because different microbes prefer different soil pH
and depending on the plant certain microbes may be required
for nutrient exchange.
Bacteria come in two basic types. Anaerobic which lives
without oxygen and produces offensive odors, and aerobic which
lives with oxygen and produces pleasant fresh odors. Bacteria
are responsible for recycling carbon, sulfur, and nitrogen.
CO2 is a by product of aerobic bacteria, and sulfur is
recycled by anaerobic bacteria.
Soil nutrients occur in two forms: inorganic compounds dissolved in water or attached to minerals and organic compounds part of living organisms and dead organic mater. Bacteria, fungi, nematodes, and arthropods are always transforming nutrients between these two forms. When they consume inorganic compounds to construct cells, enzymes, and other organic compounds needed to grow, they are said to be "immobilizing" nutrients. When organisms excrete inorganic waste compounds, they are said to be :mineralizing" nutrients.
Free-living nematodes can be divided into four broad
groups based on their diet.
Bacterial-feeders
consume bacteria.
Fungal-feeders feed
by puncturing the cell wall of fungi and sucking out the internal contents.
Predatory
nematodes eat all types of nematodes and protozoa. They eat smaller
organisms whole, or attach themselves to the cuticle of larger nematodes,
scraping away until the prey’s internal body parts can be extracted.
Omnivores
eat a variety of organisms or may have a different diet at each life stage. Root-feeders
are plant parasites, and thus are not free-living in the soil.[1]
Nitrogen found in the atmosphere can not
be used directly by plants. It must be 'fixed' through a
process called nitrification where aerobic bacteria combine
nitrogen with either oxygen or hydrogen to form nitrite
(NO2-), and eventually nitrate (NO3-) ions from the ammonium
(NH4+) waste of protozoa, and nematodes which consume other
bacteria and fungi. [1] This is an example of mineralization.
Nitrification produces an acidic pH. When oxidation occurs, an electron is lost, releasing energy
that is used by the bacteria. Nitrifying bacteria do not
generally like low pH, but fortunately other bacteria called
denitrifying bacteria convert nitrogen salts created by the
nitrification process back into nitrogen N2 which returns to
the atmosphere. The roots take up negatively charged anions (H+) exchanging hydroxy (OH-)
anions. This also helps to return the pH to a higher level.
Hydrogen is the root's currency. They sell OH- for H+, and then exchange H+ for nutrient cations. Even microorganisms carry their own charges, and are also influenced by the anions an cations of the roots and soil.
Bacteria
fall into four functional groups. Most are decomposers
that consume simple carbon compounds, such as root exudates and fresh plant
litter. By this process, bacteria convert energy in soil organic matter into
forms useful to the rest of the organisms in the soil food web. A number of
decomposers can break down pesticides and pollutants in soil. Decomposers are
especially important in immobilizing, or retaining, nutrients in their cells,
thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.[1]
A
second group of bacteria are the mutualists
that form partnerships with plants. The most well-known of these are the
nitrogen-fixing bacteria. The third group of bacteria is the pathogens.
Bacterial pathogens include Xymomonas
and Erwinia species, and species of Agrobacterium
that cause gall formation in plants. A fourth group, called lithotrophs or
chemoautotrophs, obtains its energy from compounds of nitrogen,
sulfur, iron or hydrogen instead of from carbon compounds. Some of these species
are important to nitrogen cycling and degradation of pollutants.[1]
Bacteria live in a matrix of sugars, proteins, and DNA called
Bio-film or Bacteria Slime which helps sustain them through
drought and attack from antibodies and other bacteria.
Bacteria prefer the vicinity of root hairs because of the
available food from the excudates. The nutrients within the
bacteria are unavailable to the plants until the bacteria die
and so goes the cycle. Bacteria feed on the excudates in the
root zone, absorbing nutrients which will be later be made
available to the plants when they die. There are also
Mutualistic Bacteria which live on the root nodules of peas
and beans. These bacteria trade amino acids containing
nitrogen for carbohydrates without the need for the bacteria
to die.
Pathogenic bacteria often produce toxic alcohols if the soil
has poor texture and drainage. They can cause citrus canker,
diseases of potatoes, melons and cucumbers and fire-blight of
pears, and apples, galls and tumors, root rot on onion, leaf
curl and black spot on tomatoes, but beneficial bacteria
compete strongly for food and starve out pathogenic bacteria.
By keeping your soil alive you can avoid these problems, but
intervening with "-icides" will kill the good bacteria as
well, leaving you with dead soil.
Certain strains of the soil bacteria Pseudomonas
fluorescens have anti-fungal activity that inhibits some plant pathogens. P.
fluorescens and other Pseudomonas
and Xanthomonas species can increase plant growth in several ways. They
may produce a compound that inhibits the growth of pathogens or reduces invasion
of the plant by a pathogen. They may also produce compounds (growth factors)
that directly increase plant growth.
[2]
These
plant growth-enhancing bacteria occur naturally in soils, but not always in high
enough numbers to have a dramatic effect. In the future, farmers may be able to
inoculate seeds with anti-fungal bacteria, such as P. fluorescens, to ensure that the bacteria reduce pathogens around the seed
and root of the crop.[2]
The roll fungus plays in soil is astounding. Saprophytic fungi decompose dead organic matter while mycoohrhiza fungi associate with the plant roots exchanging energy and nutrients. Bacteria are good
at breaking down the sugars in organic mater, but saprophytic fungi can
break down harder mater such as chitin and bark. We are
unable to see most of the fungal hyphae, but it can branch out
as fast as 40 micrometers per second extending it's network
over relatively large areas, and can extend down deeper than
bacteria. The fungal hyphae absorb nutrients very much like
bacteria, but they also have the ability to locate and reach
out to these nutrients. Fungi even have the ability to
attract and suck the nutrients out of unsuspecting nematodes.
Organic mater is broken down into compounds, and ingested by
acidic substances leaked out of their hyphal tips. The fungal
network transports nutrients, and water long distances to the
roots which attract the fungus with exudate.
When the fungus dies, it too just like bacteria, make the
nutrients it previously absorbed available to the plant
roots. It also leaves behind long tunnels which bacteria,
air, and water can move through.
Fungi release nitrogen as ammonium (NH4+) or nitrite (NO3-)
and other nutrients as part of their waste, which feeds the nitrifying bacteria. But the acidic emzimes produced by the
fungi lower the pH and as we know nitrifying bacteria prefer a
pH over 7. Without the nitrifying bacteria the ammonium
(NH4+) and nitrite (NO3-) will not be converted. This is not
good for most vegetables, but in general perennial trees and
shrubs prefer fungal dominated soil while annuals, grasses and
vegetables prefer bacteria based soils. You may have noticed
that mycillium is often found in forest soil.
Mycorrhizae fungus are very fragile. Chemicals, compaction,
roto tilling and double digging destroy the fungal hyphae.
Fungal Hyphae
There are two kinds of mycorrhizae. Ectomycorrhizal which
grow close to the surface and endomycorrhizal which penetrate
and grow inside the roots as well as extend outward. This is
preferred by most vegetables. A major function of Mycorrhizae
fungus is to transport phosphorus back to the plant. Copper,
calcium, magnesium zinc and iron are also moved back to the
plant. But just as important; the fungus also unlock and
change the ion state of these elements so that the nutrients
are soluble and available to the plant.
There are hundreds of endophytic fungal species. Some are
beneficial others are not, but nearly all plants are
infected. Endophytic fungal can occasionally transport
nutrients between more than one plant. Some produce toxins
that kill pests, limit seed production, increase the rate of
seed germination, cause resistance to disease, or speed the
decay process after a plant has died. Others are pathogenic
such as those that cause powdery mildew, rust fungus, or
fusarium wilt on tomatoes which can lay dormant in the soil
for more than a decade. The first indication of fusarium
wilt is yellow leaves starting at the bottom. Gardens are
filled with fungus that create vitamins, antibodies, affect
pH, kill bacteria and nematodes as well as those that destroy
a garden.
Fungal-dominated soils (e.g. forests) tend to have more testate amoebae and
ciliates than other types. In bacterial-dominated soils, flagellates and naked
amoebae predominate. In general, high clay-content soils contain a higher number
of smaller protozoa (flagellates and naked amoebae), while coarser textured
soils contain more large flagellates, amoebae of both varieties, and ciliates. [1]
Protozoa are much larger than bacteria and nematodes which
they feed up on. Protozoa are an important part of soil
because worms eat protozoa and when protozoa die they too
provide nutrient and food for the bacteria. The soil is a web
of unending transformation.
Nematode
Nematodes transport minerals fungi and bacteria. They are larger than protozoa
and are not be able to deliver nutrients to the
plant roots if the soil is compacted. Most nematodes in the soil are not plant parasites. Beneficial nematodes
help control disease and cycle nutrients.
Nutrient
cycling. Like
protozoa, nematodes are important in mineralizing, or releasing, nutrients in
plant-available forms. When nematodes eat bacteria or fungi, ammonium (NH4+)
is released because bacteria and fungi contain much more nitrogen than the
nematodes require. Grazing. At
low nematode densities, feeding by nematodes stimulates the growth rate of prey
populations. That is, bacterial-feeders stimulate bacterial growth,
plant-feeders stimulate plant growth, and so on. At higher densities, nematodes
will reduce the population of their prey. This may decrease plant productivity,
may negatively impact mycorrhizal fungi, and can reduce decomposition and
immobilization rates by bacteria and fungi. Predatory nematodes may regulate
populations of bacterial-and fungal-feeding nematodes, thus preventing
over-grazing by those groups. Nematode grazing may control the balance between
bacteria and fungi, and the species composition of the microbial community. Dispersal of
microbes.Nematodes
help distribute bacteria and fungi through the soil and along roots by carrying
live and dormant microbes on their surfaces and in their digestive systems. Food source.Nematodes
are food for higher level predators, including predatory nematodes, soil
microarthropods, and soil insects. They are also parasitized by bacteria and
fungi. Disease
suppression and development.Some nematodes cause disease. Others consume disease-causing organisms,
such as root-feeding nematodes, or prevent their access to roots. These may be
potential biocontrol agents.[1]
Arthropods
range in size from microscopic to several inches in length. They include
insects, such as springtails, beetles, and ants; crustaceans such as sowbugs;
arachnids such as spiders and mites; myriapods, such as centipedes and
millipedes; and scorpions.[1] Arthropods transport fungi and bacteria while shredding up to 30% of
the organic mater on temperate zone forest floor.
Springtail
Arthropods
can do damage to crops, but they are a valued member of the
soil web. Most live on the surface, but others such as Rugose
harvester ants ( Pogonomyrmex rugosus) are scavengers rather than predators. They eat dead
insects and gather seeds in grasslands and deserts where they burrow 10
feet into the ground. Their sting is 100 times more powerful than a fire
ant sting, but they help mix and aerate the soil while adding organic matter.
Mites
Termites and ants bring organic
mater down into the soil, and in tropical areas they mix more
soil than worms. Termites digest their food with the help of
pathogenic archea creating methane and are a major contributor
to greenhouse gas. Their populations are very important to
the soil web.
Although the
plant feeders can become pests, most arthropods perform beneficial functions in
the soil-plant system. Shred organic material. Arthropods increase the surface area accessible to microbial attack by shredding
dead plant residue and burrowing into coarse woody debris. Without shredders, a
bacterium in leaf litter would be like a person in a pantry without a can-opener
– eating would be a very slow process. The shredders act like can-openers and
greatly increase the rate of decomposition. Arthropods ingest decaying plant
material to eat the bacteria and fungi on the surface of the organic material. Stimulate microbial activity.
As arthropods graze on bacteria and fungi, they stimulate the growth of
mycorrhizae and other fungi, and the decomposition of organic matter. If grazer
populations get too dense the opposite effect can occur – populations of
bacteria and fungi will decline. Predatory arthropods are important to keep
grazer populations under control and to prevent them from over-grazing microbes. Mix microbes with their food. From a bacterium’s point-of-view, just a fraction of a millimeter is
infinitely far away. Bacteria have limited mobility in soil and a competitor is
likely to be closer to a nutrient treasure. Arthropods help out by distributing
nutrients through the soil, and by carrying bacteria on their exoskeleton and
through their digestive system. By more thoroughly mixing microbes with their
food, arthropods enhance organic matter decomposition. Mineralize plant nutrients.As they graze, arthropods mineralize some of the nutrients in bacteria and
fungi, and excrete nutrients in plant-available forms. Enhance soil aggregation.In most forested and grassland soils, every particle in the upper several inches
of soil has been through the gut of numerous soil fauna. Each time soil passes
through another arthropod or earthworm, it is thoroughly mixed with organic
matter and mucus and deposited as fecal pellets. Fecal pellets are a highly
concentrated nutrient resource, and are a mixture of the organic and inorganic
substances required for growth of bacteria and fungi. In many soils, aggregates
between 1/10,000 and 1/10 of an inch (0.0025mm and 2.5mm) are actually fecal
pellets. Burrow.Relatively few arthropod species burrow through the soil. Yet, within
any soil community, burrowing arthropods and earthworms exert an enormous
influence on the composition of the total fauna by shaping habitat. Burrowing
changes the physical properties of soil, including porosity, water-infiltration
rate, and bulk density. Stimulate the succession of
species.A dizzying
array of natural bio-organic chemicals permeates the soil. Complete digestion of
these chemicals requires a series of many types of bacteria, fungi, and other
organisms with different enzymes. At any time, only a small subset of species is
metabolically active – only those capable of using the resources currently
available. Soil arthropods consume the dominant organisms and permit other
species to move in and take their place, thus facilitating the progressive
breakdown of soil organic matter. Control pests. Some arthropods can be damaging to crop yields, but many others that are present
in all soils eat or compete with various root- and foliage-feeders. Some (the
specialists) feed on only a single type of prey species. Other arthropods (the
generalists), such as many species of centipedes, spiders, ground-beetles,
rove-beetles, and gamasid mites, feed on a broad range of prey. Where a healthy
population of generalist predators is present, they will be available to deal
with a variety of pest outbreaks. A population of predators can only be
maintained between pest outbreaks if there is a constant source of non-pest prey
to eat. That is, there must be a healthy and diverse food web.
A fundamental
dilemma in pest control is that tillage and insecticide application have
enormous effects on non- target species in the food web. Intense land use
(especially monoculture, tillage, and pesticides) depletes soil diversity. As
total soil diversity declines, predator populations drop sharply and the
possibility for subsequent pest outbreaks increases.[1]
Earthworms shred debris so other
organisms can digest it. they make the soil more porous,
increase water retention, fertility and add to the organic
mater of soil. while the inch their way through hard soil they
move nutrients, transport microbes, and create pathways for
roots, leaving behind a slime which helps to bind soil
particles together. Why then would a gardener roto-til the
soil killing the worms that were already breaking up the
soil? Then add fertilizers and pesticides which either kill
what ever worms remain or drive them away. If you have worms
- chances are you have healthy soil full of organic matter,
bacteria, archea, fungi, protozoa, nematodes and arthropods. A healthy soil wed will provide your garden with all that it
requires.
I know
this is hard to believe, but even moles and snails are beneficial. Moles aerate the soil and move smaller organisms great distances. Snails accelerate
decomposition, aerate the soil, leave slime behind that binds
particles of soil and as are all creatures they too leave
nutrients behind when they die. The snails you encounter
above ground are only a small percent of the total population,
and they are not exclusively after your crop. They consume
more than just your lettuce. Slugs and snails eat
fungi, algae, lichens, and rotting organic mater. In a healthy soil web they will be kept in
control by snakes, lizards, spiders, and birds. In return these
predators will also keep other pests under control, and help
spread fungi, and bacteria.
Predators like
centipedes, spiders, ground-beetles, scorpions, skunk-spiders, pseudoscorpions,
ants, and some mites eat crop pests, and some, such as beetles
and parasitic wasps, have been developed for use as commercial biocontrols.
And lastly here is a strange fact: Cicada live underground for 17 years before emerging, The nanopattern on their wings protect them from bacteria.
The greenhouse environment can produce over whelming problems.
Fungal problems have been common in my garden room. Humidity and a lack of air exchange are most likely the problem. This article from Associated Environmental Consulting Group goes into further detail about mold and fungus problems in greenhouses. Controlling Mold In Greenhouses - Catalogs.com offers advice for greenhouse control.
Here is a safe and natural product which I have not used but looks promising. Actinovate
Jon Parr has also taught me to use H2O2 (Hydrogen Peroxide) I now keep a spray bottle filled and handy at all times. It's great for sanitizing tools and seedlings. Yep a 3% solution is safe for your plants, you and any fish you may have. Of course I'm talking about small amounts sprayed on your plants. H2O2 converts back to H2O and O very quickly.
Jon Parr and Vlad are some of the best contributors to the aquaponic forums.
Here's a little advice they have pasted on that I appreciate.
GH (Green House) pest management has three strategies, and which is best is really open for debate.
1- intentionally low pest security, meaning wide open large screens for
honey bees, pests, and pest predators. This works pretty good for lazy
folks like myself, especially if you are planting beneficial plants to
attract the predators. No fuss about pollination, and no big concern
about sterilizing everything.
2- moderate pest security. This one is fine for new greenhouses, and
light traffic GH's with cleanly guests. Once a pest gets inside, though,
trouble trouble.
3- high security, meaning positive pressure and HEPA filters, thrips
screening, humidity and temp control, haz-mat suits and dissinfect
routines. Just the thought of all that work spoils my mood, but is
probably the smartest long term plan for commercial use.
I'm a low security type guy. Address the pest directly. Mold? Increase
airflow and temp, decrease humidity. Spider mites, fungus gnats, white
flies, aphids? Allow predators, spray with tea, nuke them with CO2.
Nasturtiums are awesome for the garden by the way; trap crop or aphids,
pest predator magnets, repel white fly and spider mites. Yep. And
borage, and multicropping.
You can use the 'ol 3-5% oil + 0.5% dish washing detergent
remedy...works well but you have to be real careful to get as little of
the concoction into your system and take measure to cover up your fish tank to
protect from overspray. And even this low % of oil will burn pepper
plants if you have any...won't damage them beyond repair or anything,
just don't be freaked out by the necrotic lesions that will be left on
their leaves. peppers seem especially sensitive to this type of
treatment.
A better/easier/more fish safe bet might be a
naturally occurring fungus called Beauvaria bassiana that will take care
of a whole host of common garden pests...spider mites included (and
then some). B. bassiana can be purchased under the trade names
Botaniguard, Naturalis-L or Mycotrol-O the later two being ok'd by
OMRI...and more importantly it is fish safe (unlike any kind of oils or
most soaps).
Whatever you spray with make sure to repeat after 3 or 4
days...then again after 3 or 4 days...and then once more...since most of
these sprays wont kill the eggs that they've laid...so make sure you
get the bastards that have hatched...and spray the under-sides of the
leaves...Good luck. Spider mites are a royal PITA.
Pythium diseases 
brown spot 
Phytophthora blight
Fusarium wilt 
blue mold
powdery mildew
leaf scorch
sour rot 
white ear rot and seedling blight of maize
bitter rot and anthracnose 
Botrytis blight 
Sclerotinia rot 
