Chapters 7.7
7.7 - Pesticide seed application
Nick Moroz, University of Guelph, Canada
Suggested citation for this chapter.
Moroz,N (2022) Pesticide seed application. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org
Introduction to Pesticide Seed Treatment and Alternative Seed Treatments
Seed treatment – the application of insecticides, fungicides and/or other growth-promoting materials to seeds – is a rapidly expanding field for pre-harvest pathogen control, working effectively to kill and reduce pests and pathogens living directly on or within seeds as well as in the soils surrounding a treated seed (Mancini & Romanazzi, 2014; Taylor & Harman, 1990). Fungi and insect pathogens, including seed-borne pathogens, can infect a variety of seeds while also harboring disease and potentially transferring infection to the next seasons’ crops (Munkvold, 2009, p.295). There are a variety of seeds vulnerable to many pathogens, including cereals and vegetable seeds, requiring sterilization and protection (Mathre, Johnston, & Grey, 2006; Mancini & Romanazzi, 2014). Pesticide seed treatments have been shown to prevent plant disease epidemics caused by seed-borne infections, while also reducing the amount of pesticides needed to manage disease (Mancini & Romanazzi, 2014). An effective seed treatment requires a relatively small amount of pesticides to treat a seed, and new systemic pesticides will eliminate the need for multiple foliar or field applications of pesticides later in the growing season (Mancini & Romanazzi, 2014; Taylor & Harman, 1990). Seed-borne pathogens are killed before they get into the field, saving money and resources.
Applications of fungicides are almost always effective (Mancini & Romanazzi, 2014). However, they can also have poor effects on their non-target environment as well as contribute to greater pathogen resistance (Mancini & Romanazzi, 2014). Furthermore, aggravated use of pesticides can pose a serious hazard to farmers applying these substances without advanced safety equipment. Although pesticide seed treatment was found to be a substantial solution to reduce overall pesticide use, alterative disease-reducing treatments to pesticide use have also been sought to completely eliminate synthetic pesticide use (Mancini & Romanazzi, 2014).
Although the main goal of this critical review is to point to the effectiveness of pesticide seed treatment, it also directs the reader to consider effective alternative treatments, including physical treatments and bio-pesticides and bio-control agents. These alternatives can be used with pesticide seed treatments or if pesticide seed treatments are not an option. Chapters on “Compost Teas” and “Surface Sterilization of Seeds” within this encyclopedia also provide more information on less-effective but beneficial technologies. Overall, modern pesticide seed treatments are a safe and affordable pest and pathogen preventative measures, leading to increased seedling survival, disease-free plants and higher yields (Taylor & Harman, 1990).
What is Pesticide Seed Treatment?
Pesticide seed treatments are specifically the application of a small amount of chemical agents to seeds in order to provide protection to seeds, at the time of planting and thereafter, against a broad range of pests and pathogens, while also helping with the establishment of healthy crops (Taylor & Harman, 1990). Plant pathogens can reduce the quantity and quality of seeds harvested for future planting seasons, and can also preserved in seed lots if they are seed-borne pathogens, leading to infection and disease in future crops (Mancini & Romanazzi, 2014). Thus, management of plant diseases is important as it directly impacts current yields, disease prevalence, and the quality of seeds that will be used for future yields (Mancini & Romanazzi, 2014).
Synthetic pesticides (fungicides, insecticides, etc.) for foliar use (i.e. pesticide leaf-spray) have some major drawbacks, as they are expensive and are typically not effective against viruses. Often foliar and soil spraying-pesticides are applied manually and in excess in regions with poor knowledge of sustainable pesticide management, posing a threat to human health and the environment. However, pesticide seed applications use less pesticide and can effectively reduce plant disease while also being much more affordable.
pesticide seed application can greatly enhance crop disease-resistance while reducing the harmful effects of aggravated pesticide use on humans and the environment. Fungicides represent a variety of modern pesticide chemicals used to treat seeds. Modern fungicides used today for seed treatment are generally low in toxicity to plant and animal life and are applied in such low doses they have a minimized impact on the environment (Mathre, Johnston, & Grey, 2006). Doses of these modern fungicides can be as low as 1 gram of active ingredient per hectare (0.4 grams/acre), resulting in a cost per hectare that is usually less than $5 per hectare and often lower than $2.50 per hectare, making seed treatment one of the least expensive growing applications on farms (Mathre, Johnston, & Grey, 2006).
The seed and crop protection industries have rapidly expanded both insecticide and fungicide seed applications since the 1990s, while also aiming to reduce the harmful impacts of active ingredients (Munkvold, 2009; Elbert, Haas, Springer, Thielert, & Nauen, 2008). This has led to systemic seed treatments that fight disease during germination, emergence, and plant growth (Munkvold, 2009). While breeding crops for pathogen resistance is key, crop protection products, such as seed treatments, are also needed to address unanticipated agronomic challenges (Munkvold, 2009). Finally, modern seed treatments can be, and is often, more than a single coating of fungicide or insecticide, and can contain several layers of active ingredients, wetting agents, colorants, and bird/wildlife repellents (DeLiberto & Werner, 2016; Munkvold, 2009).
Insecticides Seed Treatment for Fighting Pests and Pathogens
This section outlines various insecticide seed treatments, the diseases they control, the chemicals used, and their systemic/non-systemic effects on preventing insect-related plant disease. Table 1.0 outlines various seed-applied insecticide chemicals that have become widespread in the past two decades, most notably the neonicotinoid chemicals. Insecticide seed treatments only became widespread with the introduction of neonicotinoid active ingredients, starting with imidacloprid in 1991 (Munkvold, 2009; Elbert et al., 2008). Prior to this some insecticides were approved but use was often limited and sometimes dangerous (Munkvold, 2009). Imidacloprid was first used as a seed treatment for maize in 1995 and was replaced by thiamethoxam in 1997 and clothianidin in 2003 (Munkvold, 2009). Since 2000, approximately 90% of the maize planted in the USA has been seed treated with either thiamethoxam or clothianidin (Munkvold, 2009). The increased use of pesticides seed treatment in crops like maize is prevalent, and this trend is occurring for many other crops, such as in sugarbeet in the United Kingdom (Munkvold, 2009). Sugarbeet insecticide seed treatment applications went from 0% in 1993 to 75% in 2002 in the area sown to sugarbeet, corresponding to a 95% drop in overall insecticide use in sugarbeets in the United Kingdom (Munkvold, 2009). This drop occurred because soil-applied insecticides were readily replaced by insecticide seed treatments (Munkvold, 2009). Now the same seed-applied insecticides (thiamethoxam or clothianidin) are also used on canola, soybean, and cottonseeds throughout North America (Munkvold, 2009).
Adapted from: Munkvold, 2009 and aPaulsrud et al., 2001; aPaulsrud et al., 2001; bYao et al., 2006; cHainzl & Casida, 1996; dGunning et al., 1996; eNauen et al., 2003
Insecticides seed treatments can be broad spectrum, meaning they are toxic to a variety of insects, or narrow spectrum, meaning they specifically target only a one or a few insect species. Seed-applied insecticides are used to control soil-borne insects, but these compound also have the systemic ability to control above ground leaf (foliar) and stem-feeding insects (Munkvold, 2009). The modern active ingredients mentioned in table 1.0 can provide broad-spectrum, long-lasting control of pests and diseases (Munkvold, 2009; Elbert et al., 2008). Pesticide seed treatments opened the door to more seed applications, going further than simple seed-dressings to include film coating, pelleting or multilayer coating (Elbert et al., 2008). Neonicotinoids are used for seed treatment in cotton, corn, cereals, sugar beet, oilseed rape and other crops to control against a broad range of plant disease from different orders (Coleoptera, Lepidoptera, Diptera, etc.) (Elbert et al., 2008).
Fungicides Seed Treatment for Fighting Pests and Pathogens
As in the previous section, this section outlines various fungicide seed treatments, the diseases controled, the chemicals employed, and the various modes of action of these treatments that prevent fungal-related plant disease. Table 2.0 outlines various seed-applied fungicidal chemicals that have also become widespread in the past two decades, as well as some older chemicals, such as Carboxin, which was introduced in the late1960s. Historically, fungicides were developed using dangerous sulfur, copper and mercury compounds, but the toxicity of these compounds resulted in the banning of these substances for health and environmental reasons (Mancini & Romanazzi, 2014). The use of mercury fungicides continued up until the 1970s, when concerns of their toxicity in humans and animals let to their expiration (Mathre, Johnston, & Grey, 2006). Now fungicide seed treatments protect seedlings from common soil-inhabiting fungi that often cause seed rots and damping-off diseases (Paulsrud et al., 2001).
Because is environmental and health concerns, there was a need to find strong replacements that were effective and affordable, and Carboxin was the first modern systemic fungicide to act as a replacement (Mathre, Johnston, & Grey, 2006). Carboxin was found to prevent loose smut in wheat and barley and to prevent common bunt in wheat (Mathre, Johnston, & Grey, 2006). This is impressive as loose smut pathogen can survive from one season to the next by living inside the seed embryo, so the fungicide had to penetrate into the developing seed and eliminate the pathogen (Mathre, Johnston, & Grey, 2006). Carboxin was effective in this regard (Mathre, Johnston, & Grey, 2006). Now fungicides can control various plant diseases, helping farmers produce grains (Mathre, Johnston, & Grey, 2006). Table 3.0 outlines the modes of action of many of the chemicals listed in table 2.0. Readers are directed to Mathre, Johnston, and Grey’s (2006) review, which outlines many applications of fungicidal seed treatments for fighting a variety of diseases that impact wheat and barley in a useful and concise summary.
Like insecticides, fungicide seed treatments can be broad spectrum or narrow spectrum and there are various types of fungicides, including contact fungicides and systemic fungicides, in which the latter can destroy pathogens living within seed tissue (Mancini & Romanazzi, 2014). Successful seed treatment depends on the pathogen’s location within the seed (Mancini & Romanazzi, 2014). Contact fungicides do not stop internal infections and are only effective in preventing fungal spores from growing on the seed surface (Mancini & Romanazzi, 2014). Cytotropic fungicides do penetrate the outer seed layers where some fungal infections can persist (Mancini & Romanazzi, 2014). Finally, other systemic fungicides can penetrate deep into the seed, protecting against early infection from airborne and soil-borne diseases, although these fungicides are more effective later in seed development (Mancini & Romanazzi, 2014). As such, based on the fungicide’s purpose and the disease threats, farmers can select the appropriate fungicide for a particular seed treatment.
Protection of Seeds and Seedlings
Without seed treatment, it may be difficult to control for seed-borne or early season pests and diseases (Mancini & Romanazzi, 2014). Alternative treatments would have to be sought, and this could lead to the need for foliar pesticide spraying that is both harmful and expensive. Environmental stresses, including heavy rains, crusted soils, deep planting, cool soil, and very dry soils, led to ideal settings for even weak pathogens to contribute to plant population losses in young plants infected since germination and mal-equipped to survived extended such environmental stressors (Paulsrud et al., 2001).
Non-systemic fungicides or insecticides form a chemical barrier over the surface of the germinating seed preventing pests and pathogens from entering from systemic fungicides or insecticides protect the foliar parts from insects, diseases, and root rot (Paulsrud et al., 2001). Even a delay in infection can reduce plant losses due to stressors while early infection leads to more damage (Paulsrud et al., 2001). Some seed treatments last 10-14 days beyond planting, while other active ingredients can protect seedlings much longer if applied at the highest specified rate and given favorable environmental conditions (Paulsrud et al., 2001). Typically pesticide breakdown is most rapid in warm and moist conditions (Paulsrud et al., 2001). Finally, seed treatments can assist in plant-stand formation when seeds are planted in unfavorable soils or slow to germinate (Paulsrud et al., 2001; Mancini & Romanazzi, 2014).
Specific Types of Seed Treatments
Seed coating includes any process that for the addition of materials to seeds, but pesticide seed treatment itself has many forms, and seed coating can refer to seeds that have been dressed with dry powder, coated, or pelleted (Taylor & Harman, 1990). Seed dressing is when a dry formulation or a wet liquid formulation of this powder is applied to seeds and this method can be applied at the farm level (Taylor & Harman, 1990). However, these materials do not adhere well to the seed surface and active ingredients may be lost, therefore seed dressings are best applied in the form of a slurry (Taylor & Harman, 1990; Sharma, Singh, Sharma, Kumar, & Sharma, 2015). Seed coating is a formulation used with a special binders that enhance adherence of the active ingredient to the seed, increasing the seed size and shape (Taylor & Harman, 1990). Adhesives used for seed coating include methyl cellulose, dextran, gum Arabic, and vegetable oils (Taylor & Harman, 1990). Finally, seed pelleting an advanced seed treatment, changing the seed size and weight with the addition of multiple inert fillers/adhesives that also work to enhance seed growth and protection (Taylor & Harman, 1990). Seed coating and pelleting usually require treatment application machinery and, therefore, can be more expensive (Taylor & Harman, 1990; Paulsrud et al., 2001). Seed coating and pelleting has been reviewed (Taylor & Harman, 1990) and are not discussed further in this chapter.
In order for the safe application of insecticide/fungicide seed treatments, or combinations of active ingredients to seed treatments, ensure the composition of the seed treatment is thoroughly understood. The quality of the final seed treatment will depend on the treatment mixture, processing conditions, the application rate of the formulation, and the equipment available (Paulsrud et al., 2001). Seed treatments can be applied to true seeds (corn, wheat, soybean, all which have a seed coat and embryo conformation) or to vegetative propagation materials (including bulbs, corms, or tubers), such as potato seed pieces (Paulsrud et al., 2001). All pesticide seed treatment active ingredients and additives are applied to the seed stage.
Advantages and Disadvantages of Pesticide Seed Treatment
Seed treatments have many important benefits, as outlined in the above sections, but they also pose some risks that should be considered. As many of the advantages of seed treatment are mentioned above, this section will outline some of the risks and disadvantages to seed treatment to offer a critical approach.
Advantages
Seed treatments are very effective are preventing seed-borne pathogens, such as smut or bunt, by protecting seeds and attacking these pathogens when they are weak during their seed-borne phase (Paulsrud et al., 2001). Seedlings are generally more vulnerable to disease then mature plants, so the timing of seed treatment is optimal (Paulsrud et al., 2001). It should be noted that seed treatments, in protecting against pathogens and insects, can also ensure uniform stand establishment of crops, as is done for maize in many parts of the USA (Paulsrud et al., 2001). Seed treatments can also suppress root rots in some crops (Paulsrud et al., 2001). Finally, as mentioned in previous sections, new systemic seed treatments provide an alternative to traditional broadcast pesticide sprays for early-season foliar diseases (Paulsrud et al., 2001).
Disadvantages
The risks of pesticide seed treatments revolve around human, environment, and food supply exposure to pesticides. Accidental exposure to workers who produce and apply seed treatment poses a constant risk of seed treatments (Paulsrud et al., 2001). Contamination of food supplies via accidental mixing of treated seed with finished foods is also a risk (Paulsrud et al., 2001). Treated seeds are intended for planting and can be harmful if ingested. Accidental poisoning is also a concern for livestock, as treated seed can look like food to animals, and some seed treatments may require grazing restrictions (Paulsrud et al., 2001).
The treated seed itself has a limited active ingredient capacity and duration of protection (Paulsrud et al., 2001). The treatment is limited to how much active ingredient will stick to the seed, which is why seed-coatings can help (Paulsrud et al., 2001). Still, there is a short duration of protection because of the small amount of ingredient applied, the dilution of the chemical as the plant grows, and its natural breakdown (Paulsrud et al., 2001). At high-doses, a few treatments can partially cause plant-toxicity, or phytotoxicity, damaging tender seed tissue and possibly leading to lower germination and stunting, although generally treatment phytotoxicity is low (Paulsrud et al., 2001).
On a macro-level, an increase of chemical inputs in seed treatments can have the negative effects of increased pathogen resistance as well as the spreading of active ingredients to non-target organisms in the environment (Mancini & Romanazzi, 2014). Furthermore, pesticide seed treatments have been shown to significantly impact the plant rhizosphere’s (root system) fungal and bacterial communities, although the consequences of these effects must be further studied and taken in context (Nettles et al., 2016). Finally, workers can be exposed to the active ingredients of pesticides when applying seed treatments.
Seed Treatment as Part of Integrated Pest Management
Combining the use of synthetic pesticides and organic or ecological approaches is called Integrated Pest Management (IPM). The goal is IPM is to maximize crop productivity while minimizing the damages caused by pests and pathogens, while also using the practical resources available and minimizing environmental damages. IPM also aims to reduce pesticide residues from entering the food supply chain and environment, encouraging natural methods for pest control (Paulsrud et al., 2001; Elbert et al., 2008). Seed treatment is thus an integral part of IPM (Paulsrud et al., 2001). Pesticide seed treatment can control pests while reducing pesticide use per hectare, operator expose to pesticides, and can fit well into IPM programs (Elbert et al., 2008). Seed treatment can then be used in combination with biological mechanism to further control pests with IPM.
To implement IPM, identify the pests of interest and consider integrated synthetic and biological options needed to effectively manage the pest. This encyclopedia can direct the reader to other biological methods in this chapter outlined below as well as chapters on “Compost Teas” and “Surface Sterilization of Seeds” and that can be blended with the pesticide seed treatments discusses above for IPM. IPM calls for an integration of pesticide seed treatments with alternative methods for pest and pathogen control.</p.
Supplemental Seed Treatment Additives
Seed treatment products often contain a variety of additives to supplement the active ingredient, such as seed treatments with enhanced adhesive coatings in the pelleted form (Elbert et al., 2008; Paulsrud et al., 2001). If important additives are not in the initial seed treatment then they can be added to any pretreatment mixing tank before seed coating (Paulsrud et al., 2001). Be aware of the potential for redundant additives already supplied in the initial formulation in order to conserve resources (Paulsrud et al., 2001). Colorants are also a useful additive, often used to distinguish treated seeds from food grain for animals and to ensure uniformity in treatment coverage on seeds (Paulsrud et al., 2001). A specific colourant, Anthraquinone, has been shown to selectively repel birds from eating seeds treated with it, resulting from a learned avoidance of seeds treated with Anthraquinone by Avian species (DeLiberto & Werner, 2016). Anthraquinone is a common dye and a safe chemical repellent, deterring many wild birds, as well as mammals, from consuming treated seeds (DeLiberto & Werner, 2016).
Summary
In general, insecticide and fungicide seed treatments can eradicate or reduce seed-borne pathogens and are more reliable than the proposed alternative treatments, such as physical treatment, or biological controls (Mancini & Romanazzi, 2014). Despite this, alternative treatments are still often effective and sometime as effective as chemical treatments, especially physical treatments (Mancini & Romanazzi, 2014). Chemical seed treatments with insecticides and fungicides, along with alternative seed treatments, can improve crop stand quality and increase crop yields through protection and disinfection from seed-borne, and later airborne and soil-borne, pathogens (Mancini & Romanazzi, 2014).
Picture Based Lesson to Train Farmers
For the South Asian version (pictures only, text for you to insert), click this link for lesson 8.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.7_south_asian.pdf
For the East/South Asian version (pictures only, text for you to insert), click this link for lesson 8.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.7e.s.a.pdf
For the Sub-Saharan Africa/Caribbean version (pictures only, text for you to insert), click this link for lesson 8.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.7subsaharan_africa_carribean.pdf
For the Latin-America version (pictures only, text for you to insert), click this link for lesson 8.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/8.7latin_america.pdf
For North Africa And Middle East version (pictures only, text for you to insert), click this link for lesson Chapter 5. 7.7:http://www.sakbooks.com/uploads/8/1/5/7/81574912/7.7n._africa_middleeast.pdf
Source: MN Raizada and LJ Smith (2016) A Picture Book of Best Practices for Subsistence Farmers: eBook, University of Guelph Sustainable Agriculture Kit (SAK) Project, June 2016, Guelph, Canada. Available online at: www.SAKBooks.com
Resources Moving Forward
FAO on integrated pest management: http://www.fao.org/agriculture/crops/core-themes/theme/pests/ipm/en/
FAO on chemical controls for seed storage: http://www.fao.org/docrep/t1838e/T1838E1g.htm#Chemical%20control%20techniques
Website on Pesticide Environmental Stewardship: https://pesticidestewardship.org/pollinator-protection/seed-treatment-concerns/
Excellent research book of many aspects of seed treatments: Gullino, M. L., & Munkvold, G. (Eds.). (2014). Global Perspectives on the Health of Seeds and Plant Propagation Material (Vol. 6). Springer.
Excellent outline of many pests and pathogens that seed treatments can prevent, as well as the many active ingredients in seed treatments that prevent infections: Paulsrud, B. E., Martin, D., Babadoost, M., Malvick, D., Weinzierl, R., Lindholm, D. C., ... & Maynard, R. (2001). Oregon pesticide applicator training manual. Seed treatment. University of Illinois Board of Trustees, Urbana.
Queensland Government Website on Integrated Pest Management: http://ipmguidelinesforgrains.com.au/ipm-information/chemical-control/seed-dressings-treatments/
OMAFRA: http://www.omafra.gov.on.ca/english/crops/insects/ipm.html
References
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12. Nauen, R., Ebbinghaus-Kintscher, U., Salgado, V. L., & Kaussmann, M. (2003). Thiamethoxam is a neonicotinoid precursor converted to clothianidin in insects and plants. Pesticide Biochemistry and Physiology, 76(2), 55-69.
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