Spray adjuvant is a powerful tool for increasing the efficiency, reducing the amount and reducing the residue of pesticide products

Definition of Spray adjuvant 
 

Pesticide adjuvants The adjuvants added to the formulation of pesticide formulations (such as for oil phase liquid emulsification, particle wetting and dispersion, preventing particle sedimentation, stabilizing dosage forms, etc.) are called formulation auxiliaries; when pesticide products are applied, before spraying Used in the medicine barrel (or sprayer), the adjuvant that is mixed and added is called spray adjuvant, also known as tank mixing adjuvant. The main function of this kind of auxiliaries is to prevent the drift, evaporation, rebound and loss of droplets, and improve the wetting, expansion, attachment, penetration and absorption of the liquid on the crops, and finally achieve the increase, reduction and residue reduction of pesticide products Quantitative purpose. Different types and uses of pesticides require different types and dosages of spray adjuvants to achieve the best results.

In fact, the use of spray auxiliaries originated very early. As early as the end of the 19th century, it has been used in other industries. For example, in order to improve the adhesion of preparations such as sulfur, copper, arsenic, and lime, flour, sugar, and soap are temporarily added before use. Additives such as liquid, such additives can be called tank mix additives used in this industry. Around 1920, in order to improve the insecticidal and bactericidal activities of pesticides, there were reports of adding oils (as auxiliary agents) before using the pesticides. In the 1940s and 1950s, the research and development of surfactants developed rapidly, and new surfactants began to be used in agriculture. For example, non-ionic surfactants used in pesticides instead of soap liquid can improve the activity of active ingredients of pesticides; In addition, in agriculture, there are also cases where ammonium sulfate is added to improve the activity of herbicides, and the use of kerosene and surfactants can reduce the amount of herbicides used; later, there are reports on the application of trisiloxane silicone additives, which can Effectively improve the expansion and absorption of pesticides on the leaves of crops, thereby enhancing the efficacy of pesticides.

At present, pesticide spray adjuvants have been widely used, especially in the past ten years due to the increase of global harsh climate conditions (low temperature, drought, little rain, waterlogging), frequent occurrence of diseases, insect pests and weeds, the cost of development and use of pesticides and formulation products continues to increase. Increase and other factors, coupled with spray adjuvants can make the biological activity of the active ingredients of pesticides play a greater role, so that the development and application of spray adjuvants has been developed rapidly. According to expert forecasts, the demand for spray adjuvants is expected to increase to 500,000 tons in 2023, and it is currently becoming an indispensable part of the application in the field of pesticides. Therefore, skilled selection and use of the most suitable and effective spray adjuvants is one of the key factors for pesticide products to sell well in the market. The application of spray adjuvants in the future has great prospects and will become one of the effective means of pesticide application technology.

Why Use Spray Aids

Pesticide preparation products (such as emulsifiable concentrates, wettable powders, suspension concentrates, water emulsions, microemulsions, water dispersible granules and dispersible oil suspension concentrates, etc.) are all diluted with water and sprayed. During the application process, due to factors such as drift, evaporation, droplet rebound, and loss of the agent, as well as poor wetting and spreading of the agent, coupled with poor penetration, absorption or distribution of the agent, these factors will eventually act on the plants. Thinking that the medicine is very limited, it will eventually bring a certain loss (this loss is estimated to be at least 10%~15% of the medicine reaching the final target). Therefore, this is also the reason for the low spray efficiency.

In order to improve this efficiency, it is usually possible to add spray adjuvants when spraying. The ultimate goal of rainwater scouring and moisturizing is to improve the efficacy of pesticides, reduce the dosage of pesticides, increase the utilization rate of pesticides, and reduce the cost of farmers' use; at the same time, it reduces the pollution of pesticides to crops, soil, water and the atmosphere, thus protecting the ecology environment and food safety.

Types of Spray Auxiliaries

Spray auxiliaries are divided into synergistic type and application type, and from the chemical category, they are roughly divided into surfactants, silicones, mineral oils, vegetable oils, inorganic salts, etc.

1. Surfactants
The main components of surfactants are nonionic surfactants, cationic surfactants, anionic surfactants, etc. Among them, nonionic surfactants (such as polyoxyethylene fatty alcohols, fatty amine ethoxylates, etc.) are used more as spray aids. Alcohols, or/and a mixture of fatty acids and esters, or polyoxyethylene fatty alcohols plus a very small amount of silicones (the content of active substances is generally greater than 80%, and the dosage is 0.1%~0.5% of the spray volume). Since non-ionic surfactants are non-dielectric, they are chemically inactive in the presence of ordinary salt, so they remain chemically inert when mixed with most herbicides. Non-ionic surfactants help reduce surface tension and contact Corner, so that the agent can better wet, expand, penetrate, absorb, etc., improve the efficacy of the drug, and can also reduce the drift and loss of droplets and dissolve non-polar substances.

The disadvantage of using surfactants compared to other types of spray auxiliaries is that they will lose their effect when used in dry conditions with humidity below 65% or air temperature above 28°C. It has no affinity with crops, but it can dissolve the cuticle and cell membrane of crops. Mixing with contact herbicides will aggravate phytotoxicity and even death, so the safety is slightly worse.

2. Silicone
Silicones mainly refer to compounds whose ingredients are polyether-modified trisiloxane, tetrasiloxane and polysiloxane, and trisiloxane generally has the best performance. It can reduce the surface tension of the agent. For example, the surface tension of trisiloxane is 21.6mN/m, and its maximum spreading area can reach 172mm2, which can completely spread and cover the agent on the hard-to-wet leaves. Silicone spray adjuvants are mainly used in herbicides, insecticides, fungicides, foliar fertilizers, plant growth regulators and biological pesticides. Generally, it is effective in the neutral range of pH value. If it is used in the pH value of the agent <6 or >8, it will degrade rapidly and lose its effect, so the application range is narrow.

3. Mineral Oils

Mineral oil has been used in agriculture for a long time. As early as 1865, unemulsified kerosene was used to control scale insects on citrus; Oil is used in agriculture to prevent and control pests and weeds on crops, fruit trees and flowers, and has played an extremely important role. The types of mineral oils used include paraffin oil, engine oil, diesel oil, kerosene, etc. Generally, emulsifiers need to be added to form emulsions. The oil content of commercial products is 95%~98%, and nonionic surfactants are added 1%~2%. Mineral oil is mainly used in herbicides and insecticides, which can promote the penetration and absorption of pesticides on the waxy layer on the surface of plant leaves and insect bodies; it can also block the pore of pests, making it difficult for pests to breathe and suffocate to death. As people pay more attention to the environmental protection and food safety issues caused by the use of chemical pesticides, people are also forced to use low-toxic and environmentally friendly mineral oil products. At present, most countries stipulate that agricultural mineral oil with a content higher than 92% of non-sulfonated substances can be safely used on crops, while non-sulfonated substances with a content of less than 92% can easily cause acute phytotoxicity to young parts of plants.

In addition, the use of mineral oil as a spray adjuvant also has disadvantages, such as poor selectivity to certain crops, and harsh conditions of use, usually the best humidity is >65%, otherwise phytotoxicity is prone to occur.

4. Vegetable oils

Vegetable oils used include soybean oil, rapeseed oil, corn oil, linseed oil, modified vegetable oil (methylated vegetable oil, etc.), renewable resources (such as waste oil, biodiesel, esterified vegetable oil), etc. Commercial products contain 80%~85% vegetable oil and 15%~20% nonionic surfactant. When using vegetable oil tank mixing additives, it is characterized by its affinity to plants, which increases the adhesion of the agent, reduces the volatilization and drift loss of the agent, has good safety, strong permeability, and is resistant to rain erosion; good stress resistance , regardless of drought and low temperature, the effect is significant, and it is not easy to cause phytotoxicity; the applicable conditions are wide, and the effect is not limited by pH conditions, and there is no special requirement for humidity and temperature. Although it is not as good as surfactants and organosilicon-based tank-mixing adjuvants in reducing surface tension, its final control effect is sometimes significantly better than these two adjuvants, so it is more widely used in herbicides and insecticides .

5. Inorganic salts

In the application of herbicides, water is often inseparable. Many substances are often dissolved in the water used by people, such as calcium, magnesium, iron and sodium ions, especially groundwater contains more cations such as calcium and magnesium. The content of metal ions such as calcium and magnesium in the water determines the hardness of the water, and the physical and chemical properties of the water used have a great influence on the control effect of many herbicides.
The function of inorganic salt auxiliaries is to promote the absorption of herbicides and relieve the antagonism of Ca, Mg, Fe and other metal ions on herbicides. The ingredients used in inorganic salts include urea, ammonium sulfate, ammonium nitrate, superphosphate, etc. These salts can be mixed with non-ionic surfactants or vegetable oils to have a synergistic effect on contact or systemic herbicides Obviously, the added amount is generally 0.12%~0.5% of the sprayed liquid amount.

In addition, it has been reported in the literature that ammonium ions can help herbicides to penetrate the plant epidermis, which is beneficial to the absorption of herbicides by weed leaves, such as increasing the amount of bentazone infiltrated into the wheatgrass, thereby increasing the effect.

Generally, inorganic salts generally have no obvious synergistic effect when the humidity is lower than <65% and the temperature is >28°C, and the safety is poor.

Efficacy of Spray Auxiliary

1. Improve droplet performance and reduce drift

During the pesticide spraying process, the droplet size will become smaller due to the evaporation of the pesticide droplet water or solvent, which not only affects the deposition amount of the pesticide on the plant, but also increases the drift of the pesticide droplet, making the droplet It is easy to enter other environments and have adverse effects on people, animals and the environment.

The size of the droplet diameter generated during spraying has a significant impact on the risk of drift and the efficiency of liquid application and is therefore considered to be the most important factor affecting drift. The size of spray droplets is represented by the diameter of the droplets in microns. When the size of the droplets is about 100 μm, the problem of spray drift should be paid attention to. When the diameter of the droplet is less than 100 μm, it is easy to drift, and when it is larger than 100 μm, the risk of drift is not high.

The general solution is to try to improve agricultural spraying equipment and spraying techniques, such as electrostatic spraying with fine mist, which can produce a charged fine mist of 50 μm, thereby reducing drift; The mist droplets will not produce continuous sheets of liquid medicine, thus avoiding the loss of medicine from the leaves, so as to achieve the purpose of increasing (reaching) the amount of target pesticides.

In addition, if it is used for aerial defense, TIS-331 special anti-drift spray additive for aerial defense developed by Jiangxi Tiansheng New Material Co., Ltd. can be added to increase the size of the droplets, reduce the formation of small droplets, and improve the air quality. Droplet performance, anti-drift effect, also has the functions of anti-evaporation, promoting sedimentation, promoting adhesion and promoting absorption. This adjuvant is a special spray synergist developed by using advanced production technology and excellent synergistic technology, which can significantly improve the utilization rate of pesticide and fertilizer spraying. Practice has proved that it has a significant synergistic effect when combined with insecticides, fungicides, biological pesticides, foliar fertilizers and plant growth regulators.

2. Reduce the surface tension of the agent and improve the wetting of the plant surface

There are many kinds of plants in nature, with different surface structures, and the hydrophilicity and hydrophobicity of plants are also different. According to the difficulty of wetting the leaves of plants with aqueous solution, plants can usually be divided into two types: easy to wet and difficult to wet (the leaves have a hydrophobic waxy layer on the surface). Under the normal spraying conditions of pesticides, the excessive surface tension of the pesticides will not easily wet the plants, and will also lead to a large amount of pesticide loss; and when the surface tension is too low, the wetting and spreading ability will be too strong due to the large contact angle of the pesticides , It will also cause the pesticide to drip from the edge of the leaf surface, both of which will reduce the effective utilization rate of the pesticide.

Plant critical surface tension (CST) is an important parameter in the application of pesticides. When the surface tension of the spray agent is less than the critical surface tension of a certain plant, the spray liquid on the surface of the plant can be wetted and expanded. The agent greater than this value It cannot completely wet and spread on the plant surface. Since the surface structures and shapes of various plants are different, the values of the critical surface tension of various plants are also different, and there are large differences among them. Table 1 shows the critical surface tension values of some plants.

Table 1：

It can be seen from Table 1 that cabbage, rice, wheat, brome, goosegrass, and Aurora have small critical surface tension values, and they belong to plants that are difficult to wet; cucumber and cotton have large critical surface tension values, and are susceptible to pesticides. Wet plants; water peanuts, cowpeas, thorns, eggplants, peppers, loofahs, corn, and split-leaf morning glory are in the middle state.

When a certain pesticide formulation product is registered for the control of multiple crops (diseases or insects or weeds), the result may not be suitable for use on hydrophobic plants or hydrophilic plants. At this time, it must be regulated by pesticide application technology. On hydrophilic plants, if the surface tension value of the applied pesticide is lower than the critical surface tension of the target plant, it will be easy to wet and spread. The amount of liquid medicine and the droplet density per unit area of the target plant are used to reduce the loss of pesticides. On hydrophobic plants, when the value of the surface tension of the applied agent is greater than the critical surface tension of the target plant, it will be difficult to wet and spread. The critical surface tension of the target plant is used to improve the wetting and spreading ability of the target plant, thereby reducing the loss of the drug and improving the efficacy of the active ingredient. Table 2 shows the surface tension values of some surfactants (the amount of surfactant added above its critical micelle concentration (CMC)).

Table2：

For example, for difficult-to-wet plants with a waxy layer, when the surface tension or contact angle of the agent is large, it is difficult for the agent to wet and adhere to the leaf surface, thereby limiting the efficacy of the agent. At this time, adding a suitable tank-mixing aid can make the drug effect play a role.

3. Improve the spreadability (or coverage) of the liquid medicine

Spreading is the property of allowing spray droplets to increase the area covered on a target. In order to facilitate the absorption of the wetted medicament, it is necessary to increase the spread and coverage of the medicament.

Usually the leaf surface of plants has a critical surface tension (CST) lower than 35mN/m. Thus, formulations with a surfactant higher than 35 mN/m are not likely to spread well on any foliage, while formulations with a surfactant lower than CST do not ensure full spread on foliage. cloth.

Different surfactants have different spreading (or covering) abilities, and most of them have limited spreading area (except organosilicon trisiloxane surfactants). Table 3 shows the properties of some representative surfactants. spreading ability.

Table3：

It can be seen from Table 3 that the use of different surfactants can reduce the surface tension, but not all surfactants that reduce the surface tension have great spreadability. For example, the surface tension of fluorocarbon surfactants can reach 16.5mN/m, and the ability to reduce surface tension even exceeds that of silicone surfactants, but its spreading area is very small. The surface tension provided by conventional surfactants such as octylphenol polyoxyethylene ether (OPE-10), fatty alcohol polyoxyethylene ether (JFC), sodium dodecylbenzenesulfonate (ABS), etc. is generally in the range of 30~ In the range of 40mN/m, it can only roughly improve the spreading performance on the leaves of difficult-to-wet plants, and rarely achieve good results. Among silicone surfactants, only trisiloxane silicone surfactant has the largest spreading area (up to 172mm2), can provide complete coverage on both easy-wetting and difficult-wetting leaf surfaces, and is generally considered to be the best for spreading agent. The spreading properties of surfactants are also related to the concentration. For most usage ratios, the amount of surfactants should be above its critical micelle concentration (CMC). However, considering that the conditions of the spray droplets are not the same, on the waxy surface that is difficult to wet, in order to spread effectively, the surface tension should generally be between 25 and 30mN/m, which is also similar In need of the best droplet retention value.

The use of oil-based tank mix aids can also increase the spreading of droplets in some plant species, but they are not as effective as when applied to plants with a waxy layer on the surface. Their spreading properties also depend on the viscosity of the oil tank mix aid used and the amount of emulsifier used.

4. Increase the retention (or deposition) of the liquid medicine

The process of increasing spray retention on plant foliage is controlled by the interaction of many physical-chemical factors, the most important of which are the number, size, velocity, surface tension, viscoelasticity, evaporation, The drift is related to the structure of the target canopy. Studies have shown that after adding spray adjuvants, pesticide droplets are more likely to stay on weed leaves, increase deposition, promote absorption, reduce losses, and thus improve drug efficacy.

Studies have shown that for targets on easily wetted plants such as sugar beets and field legumes, the addition of spray adjuvants generally has little effect on retention when compared to water alone; Sedimentation of grains. There are also data studies that show that if the surface tension of the liquid is too small, although it can increase the deposition on hard-to-wet leaves such as pea and barley, it also reduces the deposition on sunflower and rapeseed.

The use of most surfactants (due to their surface-active properties) as spray adjuvants will increase the amount of spray deposition on difficult-to-wet foliage, promote absorption and thus improve efficacy. These can be checked and confirmed using fluorescent tracers or labeled pigments. Therefore, according to different surfactant components, their relative efficiency is not the same, and is directly related to the amount of spray liquid added. For maximum impact, the added concentration must exceed the critical micelle concentration (CMC) of the surfactant, independent of the equilibrium surface tension of the spray solution.

Although silicone surfactants have excellent spreadability, they also have negative effects. If they are added in excess, unless they have good adhesion, they will also be lost due to the spray liquid, which will reduce the retention of the spray liquid.

The use of oil spray adjuvants can also greatly increase the retention on the leaves. For example, the use of methylated vegetable oil in the sulcotrione liquid can increase the retention of methyl red on the leaves of Amaranthus retroflexus by 62.7%, far better than Use engine oil emulsion (refined mineral oil) and 885 surfactant additives (retention only increased by 4.95% and 13.2% respectively).

5. Improve penetration

Penetration refers to the process in which the agent penetrates the epidermis of the target body (plant or insect body) after staying on the target body, and enters the interior of the target body to exert its biological activity. Regardless of whether it is a plant or an insect, the outer skin is composed of a waxy layer with a certain thickness. The drug must first penetrate (or dissolve) into the waxy layer, and then penetrate the epidermis and enter the internal tissue according to its distribution coefficient. Generally speaking, as long as the agent can enter the waxy layer, it will produce a penetration-promoting effect. Therefore, some surfactants, oily substances and solvents with strong lipophilicity all have a certain penetration-promoting effect, but this penetration-promoting effect sometimes cannot meet the penetration of the drug. achieve a synergistic effect.

The penetrating agents used as spray aids in pesticides are generally nonionic and anionic surfactants. More use synergist TIS-310, wetting agent TIS-372, wetting agent TIS-386 and so on.

The main purpose of adding the penetrating agent is to increase the penetration of the liquid medicine into the surface and interior of the target body, reduce the dosage of active ingredients, increase the penetration speed and shorten the penetration time (improved the ability to prevent rainwater erosion), reduce the environmental pollution of pesticides, and reduce the impact on the environment. The impact of bad weather on pesticide application, etc. For example, using 1% Abamectin EC (1000 times liquid) on cabbage leaves, it takes more than 8 hours for the penetration rate to reach 50%. 4 hours.

For another example, the active ingredient 2mg/L biopesticide milbemycin used alone has very little activity on whitefly adults, and the control effect is only 29% after 3 days of treatment; Beamycin active ingredient 2mg/L treated cotton seedlings, 3 days later the adult mortality rate of Bemisia tabaci was 96%, 10 days and 15 days after treatment, the adult mortality rates were 67% and 32% respectively, which indicated that the addition of tank mixing adjuvant Mineral oil increased the penetration of milbemycin into the leaf cuticle, reduced photolysis and enhanced its insecticidal effect.

Azone, also known as laurozone, has stable chemical properties and can be kept in the dark for more than 5 years at room temperature. It has a good transdermal and permeable effect on hydrophilic and lipophilic pesticides. Used in pesticides, it can promote the penetration of insecticides to insects, promote the penetration of herbicides to weeds, moisten the leaves of plants, promote the absorption of drugs by plants, improve the application effect of the active ingredients of the medicine and reduce the dosage of the medicine. Thereby reducing the pollution of pesticides to the environment and lowering the cost of use. The dosage of azone in pesticides is only 0.5%~10%, but it can double the efficacy.

Laurozone is another class of high-efficiency penetrants used in cosmetics as skin penetrants. Due to its non-toxic, safe and high-efficiency permeation-enhancing properties, it has been used in pesticide dosage forms for many years and has obvious synergistic effects. Its mechanism of action is to affect the orderly stacked structure of the cell wall in the biological stratum corneum, and act on the subcutaneous lipids, increase the fluidity of the lipids, and promote the liquid to enter the target body through the surface layer, thereby increasing the transdermal penetration of the liquid Absorption, improve efficacy.

Application examples of tank mix additives

The following are examples of the application of several different types of tank mix additives in improving the efficiency and reducing the dosage of the agent.

Application of trisiloxane organosilicon additives in herbicides

Compared with conventional (hydrocarbon) surfactants, trisiloxane silicone surfactants have the ability to greatly reduce the surface tension of aqueous solutions; at the same time, they can increase the complete spreading of spray droplets on the surface of plant leaves, which is conducive to promoting Liquid penetration and absorption, and reduce the environmental pollution of pesticides. Table 4 shows the test results of the synergistic effect of nicosulfuron using the silicone QS-302 tank mixing adjuvant.

Table4：

It can be seen from Table 4 that the spray adjuvant using silicone QS-302 does have a synergistic effect on nicosulfuron; and as the amount of silicone adjuvant QS-302 increases, the effect of controlling barnyardgrass and foxtail is also better. At the same time, it can also be seen that it is not that the more the amount of silicone additives is added, the better, sometimes it is not good if it is too much (the agent is easy to lose), and the more reasonable amount of silicone additive QS-302 is between 0.02% and 0.08%. room as well.

Application in insecticide
The insecticide spinosad is difficult to control pests on tea leaves. Because the leaves have a waxy surface, the liquid medicine is difficult to wet; and it is even more difficult to spray the liquid medicine completely to the place where the caterpillars are on the plant. Using tank mix additive QS-326 silicone additive can provide wetting and spreading, making it easier to reach hidden caterpillars. There are about 2.88 caterpillars per plant on average in untreated tea leaves, and the average number of caterpillars per plant can be reduced to 1.03 caterpillars per plant with spinosad + conventional non-ionic surfactants, which can partially control the pests. However, the application of spinosad + QS-326 organic silicon adjuvant can reduce to 0.13 caterpillars per plant, and the effect is very significant.

Application in fungicides

(1) When the fungicide triadimefon was added to conventional non-ionic surfactants such as polyoxyethylene alkylphenol, it failed to improve the severity of grape fruit infection by pathogens, because the sprayed liquid was difficult to wet Each berry in a bunch of grapes.

When the fungicide triadimefon is added to QS-3240 (0.06% v/v) organosilicon additive, the area and damage degree of grape powdery mildew can be well controlled at the same time. It can help the medicinal liquid reach places that are difficult for crops to reach, very effectively reduce the chance of grape fruit being infected, and ensure that each grape fruit is fully and effectively protected.

(2) Add 0.1% v/v of QS-3240 organic silicon additive to the fungicide mancozeb, and use spray to treat peanuts infected with leaf spot disease by arachidicola 5 times (period is about 1 week). One hour after each treatment, artificial rainfall of 4 mm can better control peanut leaf spot, with a control effect of 95%. It shows that the use of QS-3240 organosilicon additive increases the anti-rainwater erosion ability of the agent, and can make the fungicide mancozeb exert excellent bactericidal efficacy.

epilogue

Spray adjuvant refers to the adjuvant added in the medicine barrel (or sprayer) when the pesticide product is applied. The use of tank-mixing adjuvants can improve the drift of droplets during spray application of pesticide products, wetting of leaves, spreading, covering, adhesion, penetration, absorption, resistance to rain erosion and moisturizing; the ultimate goal is to improve the efficacy of pesticides , Reduce the dosage of pesticides, increase the utilization rate of pesticides, reduce the cost of farmers' use; at the same time reduce environmental pollution and residues in crops, soil, water and the atmosphere, so as to obtain the purpose of protecting the safety of human beings and non-target organisms by a good environment.

The development and application of spray adjuvants can exert a great effect on the biological activity of active ingredients of pesticides. The demand for spray adjuvants is increasing and has become an indispensable part of the application in the field of pesticides. However, spray adjuvants cannot be used blindly. Different adjuvants need to be selected according to different environments and different crops. Otherwise, not only will the efficacy of the medicine not be improved, but sometimes it will cause side effects or injury. Therefore, when using spray auxiliaries, it is necessary to consider not only the physical and chemical properties of the pesticide itself, but also the nature of the target. Selecting the most suitable and effective spray adjuvant will help improve the efficacy of pesticide products, reduce the amount of pesticide used and reduce the pesticide residues. The application of spray adjuvants has great prospects, and will also become the most important tool for synergizing, reducing and reducing pesticide residues in the fields of insecticides, fungicides, and herbicides in the market, and will become the most important tool in pesticide application technology. one of the effective means.