Pest Management for the Organic Gardener

Pest Management for the Organic Gardener
Presented by Laura Karr at the Indiana Organic Gardeners Association, January 21, 2012

Effective organic gardening should be holistic.

Good plant health should be a primary goal, strong plants tolerate pest and disease attacks and weed pressure better than plants in poor health

  • Plant health depends on Suitability of the plant for the chosen location

    • Climate and microclimate

    • Good soil health: composition, structure, macro- and microorganisms, types and amounts of amendments employed, history, moisture content and fluctuations

    • Pest pressure and types of pests present, pest solutions employed

    • Plant density

    • Companion planting, succession planting, weed pressure, types of weeds present

Integrated Pest Management: a key to holistic gardening. We should consider…

  • Variety selection. Many non-GMO, organic seeds and plants, and even heirloom varieties, have inherent resistance to some insects and diseases. Opt for varieties with a good history in your zone and microclimate. Experiment! Each garden is unique.

    • Knowledge of pests, their life-cycles, how they interact with their hosts

    • Your tolerance of damage or loss (economic vs. aesthetic)

    • Using multiple approaches (i.e., integrated solutions). Try lowest environmental impact solutions first!

    • Pay attention to what your plants are telling you.

Types of Solutions

  • Biological: encouraging or supplementing natural enemies of pests

  • Cultural: companion planting, crop rotation, soil management, cover crops, trap crops

  • Mechanical: exclusion, picking bugs and pulling weeds, barriers, trapping (random or pheromone-based)

  • OMRI-approved chemicals and other materials (be aware of side effects, effects on non-target organisms and, thereby, unintended effects: resurgence, replacement, resistance). Great (though slightly dated) resource for info on approved materials:

What is OMRI?

  • Organic Materials Review Institute “Founded in 1997, the Organic Materials Review Institute (OMRI) provides organic certifiers, growers, manufacturers, and suppliers an independent review of products intended for use in certified organic production, handling, and processing. OMRI is a 501(c)3 nonprofit organization. When companies apply, OMRI reviews their products against the National Organic Standards. Acceptable products are OMRI Listed® and appear on the OMRI Products List. OMRI also provides subscribers and certifiers guidance on the acceptability of various material inputs in general under the National Organic Program.” 

    • Note that OMRI approval does not address efficaciousness, per se. Is primarily focused on identifying non-synthetic chemicals and other materials for organic growing according to National Organic Standards, which are established under the National Organic Program by the USDA.

Common OMRI materials for insect management: (tip: all will work best at targeting smaller, younger stages of insects). Read the label–it is the law.

  •  Physical Toxins

    • Pesticidal Soaps These work by smothering soft bodied insects and some of their eggs. Generally fast-acting but little residual activity. Apply to where insects congregate (generally undersides of leaves). Sometimes are phytotoxic to certain plants; test on a few leaves before fully applying.

    • Kaolin Clay A mineral that is applied as a film. Doesn’t kill insects, but works best as a physical barrier, repellent, irritant. Inexpensive.

    • Oils Several petroleum, plant, and fish-based oils are OMRI approved. Direct toward soft-bodied pests such as aphids, mites, thrips, whiteflies, and mealybugs. Test for phytotoxicity. Often applied to dormant permaculture to kill dormant insects and their eggs (smothering and cuticle disruption). On leafed out plants can suppress powdery mildew and some other fungi.

    • Diatomaceous earth A naturally occurring, soft, silica-based material that is easily crumbled into a fine white to off-white powder. Insecticidal due to its abrasive properties and affinity for lipids. The fine powder absorbs lipids from the waxy outer layer of insects' exoskeletons causing them to dehydrate. This also works against snails and slugs, but since these inhabit humid environments, efficacy tends to very low. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Moisture destroys activity. Do not inhale dust.

  • Biologicals/fermentation products

    • Bacillus thuringiensis This bacillus produces a crystalline toxin that disrupts the gut epithelium of a variety of insects, especially lepidopterans. Different varieties of B.t. target other insects, however. Rarely, if ever applied as a living organism. Must be ingested by insect, therefore is slow acting. Breaks down rapidly in sunlight.

    • Spinosad (Entrust™ and others) Bacterial fermentation product that works specifically on the nervous systems of arthropods. Especially good on lepidopterans and coleopterans. Expensive, but targeted applications can be highly efficacious. Breaksdown rapidly in sunlight, has short residual action, but is active via both ingestion and contact.

    • Beauveria bassiana This fungus is produced via fermentation technology to produce large quantities of spores. It is then applied via a formulation containing spores which can cause fungal infection in a variety of insects (depending on strain of fungus). Difficult to get consistently good results, works best under high humidity.

  • Botanicals

    • Pyrethrum Derived from the flowers of an African daisy (which can be grown in Zone 5), is a fast acting contact poison that ‘knocks down’ susceptible insects. Insects are left paralyzed by the toxic effect of pyrethrum. The normal function of the nervous system is affected, stimulating repetitive nerve discharges leading to paralysis. However, some insects are able to recover after the initial knockdown if the dose is too low. Works best with the synergist PBO, but this is not an approved NOP material. Therefore, best applied under conditions which can leave the “knocked down” insects vulnerable to other factors. Breaks down rapidly in sunlight.

    • Neem, Azadirachtin Derived from the Neem tree of India. Works as an molting disrupter, anti-feedant, an oviposition deterrent. Contact and ingestion activity. Some systemic activity when applied to roots (very crop dependent). Like most botanical insecticides, is rapidly broken down in sunlight. Requires multiple applications for best efficacy.

    • Rotenone Derived from subtropical leguminous shrubs of the genera Derris, Lonchocarpus, and Tephrosia. Very broad spectrum against insects and ticks. (timing and targeting important so as not to kill bees or other beneficials) Also pretty toxic to fish. Usually must be ingested, although there is a little contact activity. Works by inhibiting mitochondrial electron transport. Slow-acting and readily degraded by sunlight.

  • Insect Pheromones

    • Often used as tools for detecting certain pests via traps, or as attractants that lure insects to a bait or trap. Tend to be expensive. Use as a “confusant” is debatable and probably not reliable in small plots. 

OMRI-approved materials for fungal management. Info.

  • Biological Agents

    • Bacillus subtilis is a ubiquitous naturally occurring saprophytic bacterium that is commonly recovered from soil, water, air, and decomposing plant material. Under most conditions, however, it is not biologically active and is present in the spore form. Different strains of B. subtilis can be used as biological control agents under different situations. There are two general categories of B. subtilis strains; those that are applied to the foliage of a plant, and those applied to the soil or transplant mix when seeding. B. subtilis bacteria produce a class of lipopeptide antibiotics including iturins. Iturins help B. subtilis bacteria out-compete other microorganisms by either killing them or reducing their growth rate (CPL 2002). Iturins can also have direct fungicidal activity on pathogens.

    • Coniothyrium minitans is a fungus that can be utilized as a biological control against the fungal pathogens Sclerotinia sclerotiorum and Sclerotinia minor (causal agents of white mold on many plant species). C. minitans is naturally occurring and can be found in soils world-wide. This biocontrol fungus is sold as conidia (spores) which are dried and mixed with glucose. C. minitans attacks and destroys the sclerotia (overwintering structures) of S. sclerotiorum and S. minor in the soil. Normally these sclerotia will germinate in the spring and summer, producing spores that infect many crops, enabling white mold disease to develop. If C. minitans is applied either in the fall just after harvest or in early spring, many of the sclerotia will be destroyed. 

    • Trichoderma fungus Several strains of Trichoderma have been developed as biocontrol agents against fungal diseases of plants. These work by various mechanisms including: antibiosis, parasitism, inducing host-plant resistance, and competition. Most biocontrol agents are from the species T. harzianum, T. virideand T. hamatum. The biocontrol agent generally grows in its natural habitat on the root surface, and so affects root disease in particular, but can also be effective against foliar diseases.

  • Copper-containing materials Copper usually can be described as an insoluble compounds, yet its action in fungicides and bactericides is due to the release of small quantities of copper (Cu++) ions when in contact with water. Copper hydroxide is more water soluble at low pH (high acidity). It is important that this product be applied in a spray solution (such as water) at a pH above 6.0. If the solution is more acidic, phytotoxicity could occur. Bordeaux mixes are preparations of copper sulfate and calcium hydroxide (hydrated lime), working in much the same way as the newer copper fungicides, which are effective at lower rates of application. Following absorption into the fungus or bacterium, the copper ions will link to various chemical groups (imidazoles, phosphates, sulfhydryls, hydroxyls) present in many proteins and disrupt the function of these proteins. Thus, the mode-of-action of copper hydroxide (or any other copper fungicide) is the nonspecific denaturation (disruption) of cellular proteins. The toxic copper ion is absorbed by the germinating fungal spore and thus for best results copper must be reapplied as plants grow to maintain coverage and prevent disease establishment. Copper can remain active on leaves for up to two weeks unless washed off.

  • Other materials that are approved for use against fungi in specific circumstances: neem, soaps and oils, potassium or sodium bicarbonate, hydrogen peroxide, peracetic acid.

OMRI-approved materials for weed management. GOOD LUCK!

  • Some copper and iron-containing materials, some soaps.

  • Organic Weed Management (from Wikipedia–based on IFOAM info)

  • Organic weed management promotes weed suppression, rather than weed elimination, by enhancing crop competition and phytotoxic effects on weeds. Organic farmers integrate cultural, biological, mechanical, physical and chemical tactics to manage weeds without synthetic herbicides.

  • Organic standards require rotation of annual crops, meaning that a single crop cannot be grown in the same location without a different, intervening crop. Organic crop rotations frequently include weed-suppressive cover crops and crops with dissimilar life cycles to discourage weeds associated with a particular crop. Organic farmers strive to increase soil organic matter content, which can support microorganisms that destroy common weed seeds]

  • Other cultural practices used to enhance crop competitiveness and reduce weed pressure include selection of competitive crop varieties, high-density planting, tight row spacing, and late planting into warm soil to encourage rapid crop germination.

  • Mechanical and physical weed control practices used on organic farms can be broadly grouped as:

    • Tillage - Turning the soil between crops to incorporate crop residues and soil amendments; remove existing weed growth and prepare a seedbed for planting;

    • Cultivation - Disturbing the soil after seeding;

    • Mowing and cutting - Removing top growth of weeds;

    • Flame weeding and thermal weeding - Using heat to kill weeds; and

    • Mulching - Blocking weed emergence with organic materials, plastic films, or landscape fabric.

  • Some naturally sourced chemicals are allowed for herbicidal use. These include certain formulations of acetic acid (concentrated vinegar), corn gluten meal, and essential oils. A few selective bioherbicides based on fungal pathogens have also been developed. At this time, however, organic herbicides and bioherbicides play a minor role in the organic weed control toolbox]

  • Weeds can be controlled by grazing. For example, geese have been used successfully to weed a range of organic crops including cotton, strawberries, tobacco, and corn,[26] reviving the practice of keeping cotton patch geese, common in the southern U.S. before the 1950s. Similarly, some rice farmers introduce ducks and fish to wet paddy fields to eat both weeds and insects.


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