There’s a sort of principal of mutual correspondence in the limiting factors of a plants productivity, and these factors can be loosely grouped quite naturally by their functions. For example the question of “how much carbon dioxide should I use” has the functional group of photosynthesis containing the factors ‘CO2+Light+Heat+Nutrient‘, as well as being loosely factored to functions such as plant health, maturity, pests, et al. As a writer it is a peripheral goal to convey ideas in a sensible linear train as they relate to each other, but incidentally the products of topic herein were inspired by the not-entirely random contents of a grow store shelf. We have discussed base nutes and boosters so far, so let’s continue with the buffers that calibrate the devices that we monitor nutrients with.
Buff it up
Learning often constitutes finding out about what you will never truly understand. When someone asks me “why do I need to use both buffers 7 and 4/10 to calibrate my pH meter,” I can only hope that “because you do” will suffice. If not, it’s a major challenge, since the average person can hardly be bothered to read a book with a technical description. Moreover, just because someone has, it doesn’t mean they are particularly prepared to explain it. This is one of those times where nobody is attempting to juice your every penny into some trendy marketing propaganda – buffers are cheap – use them and use them often.
Buffers ’7&4′ or ’7&10′ are part and parcel of the calibration of most Grow Store pH meters. Sometimes there is a ‘single cal’ option in the instructions, but if a two-point calibration is recommended don’t opt out. You’ve gone this far, spent the money – why botch a 2 minute step that improves the accuracy? Keep your probe clean with an Electrode Cleaning Solution, and dip/swab it in water between solutions when calibrating it, and you can reuse your pH buffer for a while. As a buffer it should be able to stand up to moderate delusion and hold it’s target value.
EC/TDS Calibration Solutions, on the other hand, are not “buffers”. They dilute with every dip, so reuse is a literal contamination of the value. The thrifty thinkers salvation is ‘who really cares’, and I tend to agree; if you reuse your solution and it loses 10-50 ppm (2-10 μS/cm) on the meter, big deal. For the average person diluting liquid fertilizers from a feed chart, that much variation isn’t going to make a lot of difference.
Which EC/TDS calibration solution you need to use is dependent on what conversion factor you prefer (or your pen is limited to, as in most cases). Check the instructions that came with your meter as they often specify which solution is recommended for it. If you have already disposed of the instructions, UG Mag Issue 11 has the conversion factors of several popular TDS Meters.
The Dark Cide
Bugs bug, it’s in the name. You are thinking insect, and that’s great, but the brown blotches and wilt that plague the grass and garden are also bugs. It would require a large tome to detail the various pesticides available, so I will discuss the active ingredients found in many popular indoor gardening pesticides.
Soap (Potassium/Alkanolamine Salts of Fatty Acids), (Potassium cis-9-octadecenoic acid): One of the more under-rated indoor gardening insecticides available to us today, the insecticidal property of Soap is often misunderstood as “making leaf surfaces sticky” or “having a bitter taste”, but this is not the case. As bitter as we all know Soap is, to soft-bodied insects and mites it is much more insidious; weakening cell membranes and allowing internal fluids to weep out until the insect dehydrates. Since a soap’s function is not as a toxin, insect pests are not able to recuperate with detoxifying processes. Species targeted include: spider mites, thrips, aphids, as well as other indoor insect pests; and a high pH soapy solution will also help control fungal attacks.
Soap has a low mammalian toxicity, combined with a low-toxicity to beneficial insects such as honeybees and butterflies. Soap is not non-toxic to all plant species however, and several species such as jade, fern, and succulent species are known to be sensitive.
Pyrethrins: Extracted from the pyrethrum flower (Chrysanthemum cinerariaefolium), Pyrethrins have been used in an unrefined state for possibly over 2000 years. The compounds collectively termed Pyrethrins have been found effective at controlling a large variety of insect pests over the centuries, including thrips, aphids, whitefly, and mites. Pyrethrins are in fact a neurotoxin to all insect species. Pyrethrins are quickly detoxified by enzymes in insects (Cytochrome P450), so an immobilized insect may recover. To combat this, enzyme delaying synergists or carbamates are sometimes used in conjunction with Pyrethrins.
Aerosol Pyrethrins have a higher risk of absorption in the body through the lungs than liquid spray, so greater caution should be taken. Some aerosol Pyrethrins have synergists such as Piperonyl Butoxide which will delay detoxification within the insect, increasing the efficacy of the Pyrethrins; however piperonyl butoxide is a class C (possible) carcinogen. Lock-top foggers and aerosol dispensers can be used to reduce respiratory exposure – just don’t forget to disable the dispensers when working in the garden.
Pyrethrins are sometimes called “nearly non-toxic” or having “low mammalian toxicity”. In reality Pyrethrins should be used with caution, as they have a higher oral toxicity than Diazanon, Malathion, or DEET, and are also highly toxic to aquatic life and beneficial insects such as honeybees. Though the Pyrethrin compounds have acute toxicity in humans and animals, they are not known to accumulate in the body or excrete in milk.
Permethrin (Pyrethroid): One of the better known of the various semisynthetic derivatives of the chrysanthemumic acids is Permethrin, which has been marketed highlighting the much lower mammalian toxicity than its natural relative Pyrethrins. The lethal dose of Pyrethrins to kill 50% of a population of rats is around 200mg/kg compared to 4000mg/kg of Permethrin. Unfortunately the lower acute toxicity of Permethrin is balanced by the likelihood of human carcinogenicity, as well as observed genotoxicity in human tissue samples. Though some insecticides still contain Permethrin, it is more commonly used on children as a delousing agent. Other Pyrethroids you may see labeled on insecticides are Resmethrin, Allethrin, and Tetramethrin found in sprays targeting insect species which include the fungus gnat, mosquito, and fly.
Carbaryl: The third-most used pesticide in the USA, “the development of the carbamate insecticides has been called a major breakthrough in pesticides.” This is contextually related to the low persistence of Carbaryl in the environment compared to chlorinated insecticides, yet the use of Carbaryl is illegal in several industrialized European countries including the UK. Carbaryl is a broad-spectrum insecticide with a host of target species, yet it is also toxic to beneficial insects, crustaceans, and bacteria as an indiscriminate acetylcholinesterase inhibitor.
Carbaryl is slightly less acutely toxic than Pyrethrins, and detoxifies quickly in vertebrates without concentrating in fat or being excreted in milk, and this has led to its preferred use in US food crops. As a cholinesterase inhibitor however Carbaryl poses high risk of toxicity to humans, and has been classified by the US-EPA as a likely human carcinogen.
Malathion: The most commonly used organophosphate in the U.S., Malathion has been found to control aphids, thrips, spider mites, scales, and other common insect pests as an irreversible cholinesterase binder. Some plants such as petunias, ferns, and African violets can be injured by applications of Malathion, so if you are unsure do a small strip-test on a leaf or branch.
The toxicity of Malathion is dubious since it is has a relatively low toxicity until it metabolizes inside the human body into malaoxon, which has been found in a US EPA study to be 61 times more toxic than Malathion. If Malathion is used indoors the risk of poisoning is greatly increased, to the degree the US EPA has set standards imposing label restrictions to be clear to avoid use indoors, or in a poorly ventilated environment such as a greenhouse. The carcinogenicity of Malathion has been classified as “suggestive” due to lack of clear evidence for or against.
Diatomaceous Earth [ref. DE] (Silicon Dioxide): Composed of biogenic silica from the fossilized remains of the single cell diatoms which lived many millions of years ago, DE is today mined from marine sediments around the world. Prepared as an insecticide, it’s small shards of sharp edged silica scratch and cut at the waxy cuticles of insect bodies, eventually dehydrating and killing them. The efficacy of DE, based on the desired result of dessication, is reduced when DE (and particularly the environment the pest is within) becomes moist. Target pest species that DE is known to control include ants, centipedes, thrips, slugs, and as an aid against fungus gnats; however it is indiscriminate and can also control non-target pest specie who contact it.
DE is slightly more toxic than Sulfur, Soap or Neem Oil, but is still among the least toxic naturally occurring pesticides. DE is a registered food additive in the USA and Canada, and is Generally Recognized as Safe (GRAS). Protection is advisable when applying DE in fine powder form, as it can irritate the mucous membranes in the mouth and nose.
Neem Oil (oil of Azadirachta indica): One of the newer botanical insecticides available to consumers today is also one of the most versatile, and safe to use. Neem Oil has been found effective in controlling a wide variety of garden insect pests, as well as powdery mildew, black spot, and rust; yet is not harmful to birds, earthworms, or beneficial insects. That is not to say that all gardeners have had success with Neem Oil. Oil is not water soluble so Neem Oil must be blended into an emulsion or shaken well during application or the Neem Oil will separate and be applied in either a lower or higher concentration than intended. Neem Oil has a similar toxicity to “soap” without the skin irritation or sensitization – in fact Neem Oil has been used as topical treatment for arthritis, bruises, cuts, and even to treat cold sores.
Azadirachtin: One of the various compounds found within the Neem tree seed, Azadirachtin is highly toxic to over 200 insect species as an anti-feedant and growth regulator while having low toxicity to beneficial insects. This is because Azadirachtin must be injested to be effective, so insects which do not feed on your plants are not at risk. Small populations of honeybee’s can experience insect-growth-regulating effects if Azadirachtin is present in high quantities on flowering plants, and contaminated nectar is in turn fed to the brood. Azadirachtin has been found to control spider mites, aphids, thrips, nematodes, and other soil-born pests.
Sulphur (Powder, Paste, Dust, Liquid): One of the oldest pesticides in use is Sulfur in it’s various physical states. Sulfur has been used for thousands of years to control insect pests such as thrips and spider mites, as well as fungal pests like powdery mildew, leaf blight, fruit rot, and some rusts. Sulfur is considered primarily a fungicide with only secondary acaricidal (mite killing) properties, and caution should be taken if applying Sulphur on leaf surfaces to avoid contamination with oil-based sprays, as they react to form a plant toxin. The toxicity of Sulfur in mammals is low and it poses little risk on human and animal health; however it is considered a respiratory hazard if applied in a powder or dust state without protection.
Potassium Bicarbonate [ref. PB] (KHCO3): One of the few inorganic compounds to be accepted by Organic certification organizations around the world, PB is used to control fungal pests such as powdery mildew. Phytotoxic at rates higher than .5%, PB can be applied at any time during the crop cycle as it is relatively non-toxic to humans and is a registered food additive.
The focus of pesticides has traditionally been to kill pests. Toxicity, environmental damage, and preservation of organisms both seen and unseen have been secondary ideals. The solutions to our problems in the past have created new unanticipated problems, and eventually we’ve learned it’s most profitable to preserve the organisms which benefit our production. There has been growing interest in using natural and relatively harmless bacterium or predator insects to target specific pest species without any concerns of toxic residue or environmental persistence.
Bacillus thuringiensis var. israelensis [ref. Bt]: Another one of natures insect control agents, the bacterium Bt, has two subspecies which have been used to control different insect populations. A relief to indoor gardeners is the Israelensis variety, which has been found to control the larval stage of fungus gnats. Used primarily for mosquito control, Bt comes in various forms for use in ponds, pools, and indoor garden reservoirs. In order for Bt to be effective it must be consumed by an insect in its larval stage. Bt is not known to be toxic to humans, animals, fish, or beneficial insects, and has been the brunt of the most extensive toxicology testing of any bio-control agent used today.
Predatory Mites: Phytoseiulus persimilis are commonly available from Nurseries and do well in flats of bedding plants, however indoor gardeners often do not have any luck with them since they do not climb taller plants or tolerate low humidity. Neoseiulus californicus is more tolerant of temperature and humidity extremes than the persimilis, but californicus is still relatively sensitive and should be applied during moderate conditions, particularly when the soil is cool. Mesoseiulus longipes are suitable for high temperatures and low humidity, and is frequently used on taller plants. Longipes’ uniqueness is in it’s ability to thrive in lower humidity conditions than its peers. Galendromus occidentalis is a prize Predatory Mite that thrives in hot and dry conditions, yet can tolerate stages of higher humidity. Commonly used on tall plants, the occidentalis can sometimes be purchased with some mild resistance to insecticides; yet as versatile as occidentalis is this variety is intolerant of extreme cold. No matter which Predatory Mite you chose, keep in mind they all have a range of environmental tolerances, but extreme conditions can be fatal.
Ladybugs (Lady beetles), (Ladybirds): An object of superstition and folk-lore, the gardeners winged companion has been known to be a beneficial insect for several hundred years. There are thousands of species of Ladybug, and some have been imported into North America for pest control, that have since began to out-compete native species. Ladybugs have an insatiable appetite for aphids, and their larvae have been described as alligator-like with powerful aphid-crushing jaws. If aphids are in short order Ladybugs will also feed on scales, mites, and other small insects as well as pollen or nectar. Some specie of Ladybug even prefer mites or scales over aphids. It should be noted some species may require pollen or nectar in order to complete their life cycle, which can be limited in indoor gardens.
Beneficial microbial bio-controls
The term “beneficial” is redundant when relating to a bio-control. The terms are used loosely here, as there are bio-controls which have alternative benefits to plants, and vice-versa. The term is sometimes questionable, as when the cascade of effects from introducing “beneficial” organisms turns bad. Too much of a good thing, right.
Entomopathogenic Nematodes [ref. EPN]: Though they do not often see the spotlight, the endoparasitic EPNs have been found to suppress populations of insect root herbivores. Target pest larva, such as fungus gnat or flies, are invaded by the EPNs through an orifice such as the mouth or anus. The mutualistic Xenorhabdus or Photorhabdus bacterium are released by the nematode into the host larva, where enzymes break down its internal structure for the nematode to ingest.
Because EPNs and their symbiotic bacteria cannot develop in vertebrates, there is no mammalian or human risk associated with EPNs. Within the microbial community however, there may cascading effects, as studies have shown a reduction in plant-parasitic nematodes with the introduction of EPNs. EPNs are predators and will often also consume other nematodes, which in turn can raise bacterial and fungal populations. At first glace this seems good, but the other nematodes EPNs eat provide important roles in the nitrogen cycle.
Mycorrhiza Fungi: Considered by many the mechanism which gave aquatic plants the advantage needed to migrate to land, fossil evidence suggests fungi have formed mycorrhizal relationships with plants for hundreds of millions of years. These primitive fungi, known today as Arbuscular mycorrhizas [AMs], have mutualistic symbiosis with over 90% of land plant families, including many indoor and field food crops. Other groups of mycorrhizas have adapted from AM, each independently, and likely a result of coevolution with specific plant host species, such as ectomycorrhizas.
AMs infect host plant specie by penetrating epidermal or cortical cells, and enter the root system, where nutrients extracted by the fungi’s absorptive hyphae in the soil can be exchanged for carbohydrate root exudes. Since the mycillium of the fungi have more surface area than plant roots they can absorb more mineral nutrients, in turn providing more resources to the plant than it can acquire alone.
Trichoderma Fungi: Present in all soils and commonly isolated from forest or agricultural lands, Trichoderma fungi are used as a bio-control agent against fungal pests such as botrytis or fusarium. Trichoderma fungi parasitize other fungi, inactivating enzymes, and invading hyphae of plant pathogens. Trichoderma colonize root surfaces or cortex, sequester and dissolve otherwise immobile minerals, and have also evolved mechanisms which actually improve root growth.
Bacteria: The types of bacteria and their diverse roles in all scales of a garden’s ecology are far too numerous to note. In recent years there has been a noticeable shift towards bacterial isolates; nitrogen fixers, hormone and enzyme synthesizers, nutrient mobilizers, and one strain which even has natural fungicidal activity. Bacteria ultimately require carbon, and their means of acquiring carbon defines their nutritional groups. Monosaccharides, or simple sugars, are generally provided in carbohydrate products, which are suitable to feed most beneficial bacteria.
Microbial brew systems are available at Grow Stores, along with various prepared ingredient to make fresh microbial inoculations from home. Fresh-brewed “microbial teas” often produce highly diverse populations of fungi, bacteria, protozoa, and nematodes, to enliven any garden; and are a good way to avoid any cascading negative effects from inoculating with too much of one microbe or another.
Next up: Grow Store 104 – Meters, Monitors, and Controllers of the New World Grower