Analysis of application of fungicides against wheat scab

1 Brief introduction of wheat scab



Wheat scab is common in the world, mainly causing seedlings, ear rot, stem rot, stalk rot and ear rot. From seedling to heading, it can be harmed. The most serious impact is ear rot, which is the most serious damage in wheat. One of the diseases. The disease is caused by a variety of Fusarium. There are non-sexual fungi such as Fusarium graminearum, Fusarium oxysporum, Fusarium oxysporum, Fusarium oxysporum, Fusarium oxysporum and other fungi. Among them, Fusarium graminearum has the strongest pathogenicity. The sexual state is Gibberella zeae, belonging to the Ascomycetes subfamily fungus.

 

Wheat scab does not only affect wheat yield, but also reduces yield, reduces wheat quality, reduces protein and gluten content, reduces flour yield, and significantly affects processing performance. In addition, the pathogen of scab can produce a tertiary carcinogen, vomiting toxin DON, which poses a threat to human and animal health and life safety, and wheat that is seriously infected with the disease cannot be eaten. It is called "cancer" of wheat.

 


2 Overview of the registration of fungicide products for the control of wheat scab


At present, the wheat varieties cultivated and cultivated have generally poor resistance to scab, and chemical control is still the key to reduce the incidence of wheat scab. According to the data of China Pesticide Information Network, there are currently 307 preparations for wheat scab in China (as of March 2019), of which the number of registered methicillin (61) is more. Ketone (35), tebuconazole, prochloraz (32), carbendazim (31), tebuconazole, carbendazim (18), and thiram (12), accounting for the total registration certificate The number of 61.56% involves 30 related active ingredients, mainly: carbendazim, thiophanate-methyl, tebuconazole, prochloraz, thiram, triadimefon, epoxiconazole, hexaconazole, Sulfur, Jinggangmycin, enestrobin, cymene and the newly approved prothioconazole in 2019.

 

From the perspective of the registered product structure, the products are mainly concentrated in carbendazim and its compound, thiophanate-methyl and its compound, tebuconazole and prochloraz, in the face of increasingly serious scab disease, lack of effective Registered varieties that control the disease. Cyanolide has been well received by the market for its special prevention and control of wheat scab and a significant reduction in gibberellin. It has become a frequent visitor in government procurement projects. There is also the latest approved mexazole, prothioconazole and its combination in 2019. According to the research results, these new ingredients have high efficacy and will become a popular promotion product in the wheat scab market in the future.

 

From the structure of the registered company, among the 307 registered products, only Japan’s Soda Co., Ltd. registered two single-dose products of thiophanate-methyl, and Andorma Maxim Co., Ltd. registered tebuconazole and For the combination of prochloraz and Bayer, Bayer has registered a mixture of tebuconazole and trifloxystrobin. Other multinational companies headed by Syngenta have not registered any products specifically for the control of wheat scab. Although we can't speculate on the marketing strategy of multinational companies, we can still do something to prevent and control the market share of wheat scab.



3 analysis of main fungicide varieties



3.1 Carbendazim



Carbendazim is a benzimidazole fungicide. It is effective against many ascomycetes and deuteromycetes. Therefore, it has a high control effect on wheat scab. It is the earliest traditional medicine for the control of scab. It has a long service life and is recognized by farmers. High and low cost.

 

Due to the long-term, single, repeated use of carbendazim, the resistance of scab to carbendazim is continuously improved, and the effect is deteriorated. According to the relevant agricultural experts, with 50% carbendazim 100g/667m2, the control effect on scab is less than 70%. Secondly, carbendazim can significantly stimulate the pathogen to produce DON toxin, making its resistant strain more virulent. In addition, carbendazim was used at the ear of wheat, and the amount of carbendazim in the grain was large, which affected the quality of wheat.


 

3.2 Methyl thiophanate


Like carbendazim, thiophanate-methyl is the benzimidazole fungicide, which can be converted into carbendazim in plants, which interferes with the formation of spindles in mitosis and affects cell division. Therefore, its control mechanism is similar to that of carbendazim, but compared with carbendazim, it has strong systemicity and long-lasting effect. For plants that have already been infected, the control effect is better than carbendazim.

 

The same problem as carbendazim exists. Long-term single use is susceptible to resistance and cross-resistance with benzimidazole fungicides.




3.3 Prochloraz


Prochloraz can inhibit the biosynthesis of ergosterol, has a protective and eradicative effect, and has significant control effects on various crop diseases caused by ascomycetes and deuteromycetes. It is low in toxicity to beneficial organisms in the soil, but inhibits fungi in certain soils. Mainly used for fruit preservation and seed treatment, prevention of melon and vegetable anthracnose and spot disease (leaf leaf spot, brown spot disease, etc.).

 

In fact, the single dose of prochloraz in the wheat scab is less, but its compounding with tebuconazole is currently the promotion product for the control of wheat scab, and the number of registered plants is 31, ranking third. The results showed that the disease rate and disease control of tebuconazole and prochloraz 25g/667m2 were 91.46% and 91.12%, respectively, which was significantly higher than that of prochloraz 50g/667m2. %, disease refers to the effectiveness of 80.61%.




3.4 Tebuconazole


Tebuconazole, like promethamine, is an inhibitor of ergosterol synthesis and has a good control effect on diseases such as powdery mildew and rust. Tebuconazole is a highly effective drug for the control of wheat scab. Bayer has registered 430 g/L tebuconazole suspending agent and 75% tebuconazole·mycophenolate water dispersible granules to control wheat scab. A number of pharmacodynamic tests have proved that the use of triazole drugs such as tebuconazole and epoxiconazole alone to control wheat scab can require better control at higher doses, and its efficacy is greatly increased with the use of drugs. Significant rise, but excessive drug use may inhibit wheat growth and affect wheat filling and fruiting. It is usually mixed with prochloraz, cymene, and thiazolone to reduce the amount of tebuconazole. It has better safety for wheat and more stable control, which significantly reduces the content of DON toxin in wheat grains. To improve the quality of wheat.

 

In recent years, pentazole and prochloraz have become the epidemic drugs registered for the control of wheat scab. Reasonable use has good control effect on wheat scab, and the efficacy is up to 80%. At the same time, it is against wheat powdery mildew. Rust also has a good effect. In view of the current relatively single market for the control of scab, the product is one of the ideal agents for the control of wheat scab.



3.5 cymene ester


Cyanolide is a cyanoacrylate compound and is a specialized bactericide of Fusarium spp. It can strongly inhibit the mycelial growth of pathogenic bacteria such as Fusarium graminearum and Fusarium oxysporum in Fusarium. It plays a huge role in the prevention and control of wheat scab, not only is it efficient, but also greatly reduces DON toxin. Studies have shown that the use of cymene can reduce the scab index and mycotoxins by more than 80%, so that the toxin content in the grain is in full compliance with national and world standards, ensuring food safety. Secondly, cyprodin also enhances crop stress and improves crops by drastically reducing superoxide radicals, reducing peroxidation products MDA (malondialdehyde), increasing antioxidant enzyme activity, delaying crop senescence, and increasing chlorophyll. Yield. Field trials have shown that cymene can increase wheat yield by more than 13%. In addition, the cost of cymene is low, and the wheat seeds are well sold after use, which increases farmers' income.

 

Because of the high control effect, stable effect, reduced toxin level and improved stress resistance of cyanidin, the product has become the most popular alternative to wheat scab. However, the cyanolide has a single site of action and strong selectivity, and there is a certain risk of resistance. In 2017, Zhejiang has reported that 25% cymene emulsifiable concentrate is not ideal for wheat scab, and the disease control effect is 51.6%. Because cyanobacterial is a specialized bactericide of Fusarium, it has poor control effect against other rot and powdery mildew. If it is not used together with other medicinal agents, it will affect the growth and development of wheat ears, and the hairy hair of wheat ears will be affected. Poor. Cyanolide is one of the pesticides produced in China. It is produced and registered by Jiangsu Pesticide Research Institute Co., Ltd. However, due to its patent reasons, other companies have limited production, which is one of the reasons for the small number of active ingredients registered. The earliest product of cymene ester was registered in the market in 2012. It can be seen that the product has just entered the market, and compounding with triazole products such as hexaconazole and tebuconazole can slow down the production of drug resistance. Therefore, the active ingredient There is great potential in the market for the control of wheat scab, and further product development is needed.

 

3.6 prothioconazole


Prothioconazole is a sterol demethylation (DMI) inhibitor that not only has a good systemic action, but also has excellent protection, treatment and eradication activities, and has a long-lasting effect. A large number of field trials have shown that prothioconazole not only has good safety to crops, but also has good anti-disease and curative effect, and has obvious yield increase. Because of its broad-spectrum bactericidal properties, it can almost control all diseases of wheat crops. Therefore, some researchers have studied its control effect on wheat scab. Field efficacy tests have shown that 25% prothioconazole WP can be used. At 80% or more, the rate of diseased spikes in wheat milk ripening stage and maturity stage did not change much, and the yield increase effect was significant, and the DON content in the grain was significantly reduced. Spraying 48% prothioconazole suspending agent on wheat at a dose of 25 mL/hm2 was better than 25% cymene 180 mL/hm2, which was significantly higher than 50% carbendazim 750 g/hm2.

 

At present, there are four products for the prevention and control of wheat scab in the latest public registration, and there are three products containing prothioconazole. It is understood that there are many projects in the field trial of prothioconazole, and the future of this component can be seen. There must be a place in wheat scab.



3.7 Pyrenazole


The same mechanism of action exists for mexazole and prothioconazole, except that the cis-trans isomer of the active ingredient has high activity. Compared with traditional fungicides, the dosage is extremely low, and the range of control of cereal plants is very wide. It can also regulate the growth of rapeseed and increase its yield.

 

The study of the active ingredient on wheat scab is also limited to the efficacy test, and the number of reports is not large. Studies have shown that 6% mexazole water has a good protective and therapeutic effect on wheat scab, compared with carbendazim, the amount is small, the control effect is high, and the wheat stripe rust and other leaf diseases are also treated. It is a highly effective agent for controlling wheat diseases. And methotrex has a report on the efficient and safe prevention and control of wheat scab in foreign countries, which can effectively reduce the incidence and severity of wheat scab. In addition, the study of 60% meconazole·fumei double wettable powder has better control effect on wheat scab and higher safety for wheat growth. The results showed that 60% of mexazole·fumei double wettable powder 900g/hm2 was sprayed at the initial flowering stage and early grouting stage, and the control effect on wheat scab was 94.33%, the effect was very significant, and the growth of wheat was safe and no. Drug damage. These literature studies indicate that the effect of meconazole on wheat scab is still very significant, and manufacturers have successfully registered 8% mesazole suspension for the control of wheat scab, so it can be deeply studied and registered The product is used to control scab.

 

3.8 Fluconazole Hydroxylamine


Fluazolidinyl hydroxylamine is a SDHI fungicide. According to Syngenta, flurazol hydroxylamine is the most active against leaf spot and powdery mildew in all chemical groups, and the breakthrough control of cereals is caused by Fusarium. Diseases such as wheat scab. The results showed that the Fusarium graminearum exhibited high indoor activity and superior field control (up to 90% control effect), while also reducing the content of DON toxin in wheat grains (reduced by 55.09%) and increasing wheat yield. (increased production effect 127% ~ 135%). Therefore, it can be used as an alternative or backup agent for controlling wheat scab in production, and has high market value.

 

At present, the United States has registered flurazol hydroxylamine + propiconazole for the control of wheat scab, but the active ingredient has not been registered in China, only Swiss Syngenta applied for the product registered in wheat scab (SY201502694), and There are long restrictions on patent protection (Chinese patents until November 30, 2029), and other companies cannot put the product on the market in a short time.

 


4 Summary and outlook


In view of the fact that carbendazim, a commonly used agent for the control of wheat scab, has developed resistance in some areas and can stimulate wheat to produce toxic DON, affecting the quality of wheat, it is urgent to find a good alternative agent. At present, it is more recognized in the market to select a mixture of tebuconazole and prochloraz and a related product of cymene. The combination of different active ingredients is the most common and direct means of controlling wheat scab, and can delay the development of drug resistance. Cyanolide has a strong specificity in wheat scab, which is different from other product selling points. It is difficult to compete with it, but this product and triazole products ( tebuconazole, hexaconazole , epoxiconazole, etc.) have good complementarity and synergy, so the triazoles can be selected for screening tests. In addition to triazoles, it is also possible to start with methoxy acrylates (such as pyraclostrobin) and SDHI fungicides (fluopyram, etc.) to find a highly effective compound for wheat scab. A powerful complement to the control of wheat scab.