Using Environmentally Responsible Products When Spraying for Pests and Disease
The IPM Approach
Pest control in the garden should preserve the remaining biodiversity within our urban environment. By implementing Integrated Pest Management (IPM) practices into your pest control programs, you are choosing to treat with the future in mind. I believe it is our responsibility to utilize practices that are environmentally responsible. I will briefly describe just a few sustainable pesticide options used for controlling common plant pest issues.
What are IPM Practices?
The tools included in an IPM approach include good cultural practices, proper planting, using products that have little to no impact on the environment, low-persistence chemicals, and other sustainable practices. Conventional pesticides are meant to be used as a last resort. By establishing a threshold, we can determine when it’s necessary to bring in the big guns (conventional pesticides). Using safe and environmentally friendly products such as the three listed below reduce the risk of pest resistance.
How to spray for plant pests using environmentally safe products
The following options listed below lack the residual properties of toxic conventional pesticides. Neem oil, horticultural oil, and horticultural soaps reduce pest populations effect organisms that are being sprayed during the application rather than leaving behind persistent chemicals that are meant to kill long after the time it has been initially applied. Using these earth-friendlier products will require several applications for good control considering the fact that these products “kill” from direct contact. When applying these products it is extremely crucial to thoroughly cover the entire plant material.
Products in this discussion include the following:
neem oil
horticultural oil
horticultural soap
Chemicals easily become absorbed into the environment when sprayed or applied into the ground. Using these three options reduces the negative impact of heavier pesticide accumulation.
Mark and I treated our client’s beloved citrus tree for whitefly and other soft-bodies pests using a mixture of neem oil and citrus foliar fertilizer. Mark removed rotting fruits, foliage covered in high masses of whitefly, and pruned necessary branches and twigs. The pruning and removal of plant material not only provided a better structure, but it also provided more air circulation. Both the pruning in combination to the neem oil application are practices following IPM guidelines.
Neem Oil
Neem oil is extracted from the neem tree (Azadirachta indica). Neem trees are grown for their essential properties including insecticidal, fungicidal, anti-ulcer, nitrification inhibiting, and other medicinal uses. Neem trees are given the Sanskrit name “arista” which translates to ‘perfect’ and ‘imperishable’. Neem seeds, bark, and leaves contain many components (about 100 compounds), used for horticultural purposes such as mulching and nitrification inhibitors. One of the most important components found in the neem tree is its secondary metabolite called azadirachtin.
How does neem work?
Neem’s insecticidal properties are triggered during insect feeding. One important neem component is the naturally occurring chemical azadirachtin, which mimics insect growth regulators (IGR). Once ingested, the constant presence of these hormones are prevent the insect from maturing (no to puberty!). By interrupting insect metamorphosis, you are able to prevent insects from reaching adulthood - the affected insects are no longer able to produce offspring. Studies have also shown azadirachtin prohibiting insect feeding by invoking a vomit-like reflex. The affected nymphs (younger insects) eventually starve and die.
Clarified hydrophobic extract is another neem oil component. This substance is collected during azadirachtin extraction. The clarified hydrophobic extract “eats away” the outer layer found on soft-bodied insects causing desiccation.
Plant Diseases Control
Neem oil is often used in Southern California for treating a variety of flowering plant, shrubs, and trees for powdery mildew. Rose rust diseases are also treated with neem.
Environmental Impact
Neem oil applications are a great alternative to broad-spectrum conventional pesticides. Conventional pesticides persist in landscapes, ultimately throwing off the limited natural balance available within an urban setting. Beneficial insects such as predatory insects and pollinator populations are negatively affected by the persistent active ingredients by feeding on the insects that have been treated by the pesticide and/or from pollinating flowers containing lethal toxins provided by the pesticide. Conventional pest contributing to a greater imbalance between predator and pest ratio.
Assuming that adult-stage pollinators do not typically feed on the treated plant material, they are not susceptible to neem oil applications.
Easily degradable
Generally non-toxic
Neem trees grow fairly quickly and are drought tolerant which makes them a sustainable resource
CAUTION: Aquatic organisms have shown susceptibility to neem poisoning but is relatively non-toxic to mammals and birds. We highly recommend refraining from treating plants near storm drains or bodies of water.
Citrus fruit from citrus tree showing signs of whitefly
Horticultural Oils and Soaps
Unlike conventional pesticides, horticultural oil use will not cause insect resistance due to the nature of its mechanical mode of action (I’ll explain this later).
Several applications are required with several days or 1-2 weeks apart (depending on what the label states).
Most product labels usually suggest follow-up applications 7-14 days apart. Each product has its own specialized formula, thus following the product’s unique label is crucial.
Oils
horticultural oils: processed from petroleum or vegetable based oils
Farmers back in the day used a heavy oil called “dormant oil” for their agricultural pest control applications. These heavy oils had the potential to burn precious plant tissues. The petroleum-based dormant oils are only suitable for woody plants and were specifically applied during the plant’s dormant periods. Horticultural oils used today, in an agricultural and greenhouse setting have been refined and processed for the regular use of the average plant lover. The tender plant tissues (I’m mostly referring to houseplants and other sensitive species) benefit from the lighter and less phytotoxic horticultural oil. By modifying the more harsh dormant oil material, our friendlier commercially available horticultural oil use is no longer restricted to only woody plants.
Do not confuse horticultural soaps with laundry or dishwashing soap concoctions. Household soaps may be to plant material!
How do horticultural oils work?
The oil physically suffocates insects, mites and their eggs rather than poisoning them (mechanical mode of action). When sprayed directly onto the insect, their spiracles (breathing tubes) become coated in the oil which restricts important physiological functions such as gas exchange. When using using horticultural oil, coverage is critical. You must spray the underside of leaves, the top of the leaves, stems and petioles, and anywhere else containing pests.
Do not spray flowers! Oil will cause damage to delicate parts including the flowers.
Spiracles found on a sharpshooter
How do horticultural soaps work?
horticultural soaps: potassium salts from fatty acids
Although soaps have been used to control agricultural pests for over 200 years, we have yet to fully understand the mechanisms behind horticultural soaps. Several scientific papers state that the membranes of soft-bodied insects are degraded by the potassium salts sourced from the soap’s fatty acids. An insect’s outside waxy layer becomes desiccated once cuticles are coated with soap. Essentially, soap applications are insecticidal and miticidal due to dehydration.
Unlike conventional chemicals, horticultural soaps will not help control hard-bodied chewing insects, such as beetles.
Be weary of horticultural soap overuse. The accumulation of salts causes phytotoxicity in plants.
Horticultural soaps also control pest populations mechanically, which means pest resistance will not be an issue. It is, however, only effective on soft-bodied insects.
plant disease control
Prevents the spreading of fungal disease
Both horticultural oils and soaps have shown control over powdery mildew, black sooty mold, and honeydew. Spores of each fungal disease are desiccated by both oil and soap applications.
environmental impact
Lowered risk of pest resistance
Beneficial insects may return to the treated plants
Low toxicity
Although it is likely for beneficial insects to be covered by the oil or soap during applications, the re-entry of beneficial insects such as predatory mites and parasitic wasps will occur naturally due their non-residual property.
A rough summary of the sustainable spray options
Always, always, always, always, read the label!
Reading the label of each product used during your plant pest management is essential for you and your plant’s health. Successful pest control applications result from following directions provided by both professionals and available literature. Please feel free to contact us regarding any questions about horticultural pest control options. We are here to help!
