Identification of Common Maize Diseases and Their Prevention and Control Methods

Xiaochun HUANG Huihui CAO Ruihuan DU Yajing WANG Shuhong ZHANG Liwu HAO Yanpo YAO Chaohui LI Jinwen ZHANG

Abstract   Agriculture is the basic industry of China’s economic development， and maize is an important part of the agricultural economy. With the increase of global environmental warming and industrial pollution， as well as the adjustment of agricultural planting structure and the transformation of farming and cultivation methods in China， the breeding of maize varieties has been accelerated， and the planting area has increased rapidly， resulting in the condition that the occurrence of maize diseases and pests has been increasing. The damage of some minor diseases continued to increase nationwide or in local areas， and rose to major diseases， and some new diseases appeared in production， posing a threat to the safe production of maize. This paper summarized the occurrence status of important maize diseases in China， and put forward corresponding prevention and control countermeasures.

Key words   Maize; Disease control; Maize yield; Pests and diseases; Control measures

Maize is the main food crop in China， and its yield has an important impact on China’s food security. The production areas of maize in China are mainly distributed in the three eastern provinces， the Huaihai Plain and the southwestern mountains  [1] . Maize is an important food crop， as well as an important feed crop in China. It has strategic significance in the development of animal husbandry and aquaculture in China， and is also widely used in medicine and chemical industry. Therefore， with the increase of social demand for maize， the sown area of maize has grown rapidly since the beginning of the 21  st  century. According to the survey data released by National Bureau of Statistics， the sown area of maize in 2012 was 35.03 million hm 2， and achieved a total output of 205.614 million t， more than rice. Maize has become the largest grain crop in China  [2] . In 2015， the maize sown area and total yield both hit record highs， reaching 38.119 million hm 2 and 224.632 million t， respectively  [3-4] .  Through the investigation， it is found that the main diseases and pests affecting maize production in recent years are maize northern leaf blight， maize southern leaf blight，  Ustilago maydis  （DC.） Corda， bacterial wilt，  etc.  Their occurrence is closely related to cultivars， water and fertilizer management， temperature， humidity， light and wind. According to the results of the above investigation， this paper proposed some practical preventive and control measures for these common diseases.

Main Types of Maize Diseases 

Maize northern leaf blight 

Maize northern leaf blight， also known as stripe disease， leaf spot，  etc. ， is a main leaf disease of maize. Northern leaf blight is a disease that often occurs during the growth of maize. When this disease occurs， irregular spots appear on the leaves of maize， and the spots continue to spread and threaten other parts of maize. As the disease progresses， the spots change from a water-soaked state to bluish-gray and become more severe， leading to the death of maize plants  [6] .

Occurrence regularity

Maize northern leaf blight mainly damages the leaves， and can also damage leaf sheaths and bracts in severe cases. It usually occurs first from the bottom leaves， and gradually expands upwards， and spreads throughout the whole plant in severe cases. Large nucleus-like lesions form on infected leaves. They are small watery bluish-gray or gray-green spots at the beginning in the field， then expand into large diamond-shaped or long-spindle-shaped spots with dark brown edges and light brown or gray centers. They are generally 5-10 cm long. When it is wet， there is an obvious black-brown mold layer on the lesions. In severe cases， the lesions are combined with longitudinal cracks and the leaves die.

Prevention and control strategy

It is necessary to screen and promote high-yield， high-quality， disease-resistant maize varieties. Under the current conditions， matching planting should be promoted. Maize stalks should not be piled on the field， and it is advocated to compost them at a high temperature， and carry out deep ploughing and winter irrigation to eliminate the initial infection sources. Rotational planting should be adopted to avoid repeated crops and reduce the accumulation of pathogens in the field. Sowing should be carried out appropriately early to cultivate strong seedlings， and attention should be paid to fertilization and water management. Nitrogen and phosphorus should be applied in combination to enhance plant disease resistance. According to the transmission route of diseases， diseased plants can be removed in the field and the lower diseased leaves can be removed early to  reduce  the sources of the fungus.

Chemical control： From the end of the heart leaf stage to the tasseling stage or the initial stage of the disease， 750 g of 50% Haosujing wettable powder or 900 g of 80% sancozeb wettable powder is sprayed per hectare for 3 times. Commonly used agents also include 50% carbendazim WP 500 times dilution， 50% thiophanate-methyl WP 600 times dilution， 75% chlorothalonil WP 300 times dilution， 25% benomyl EC 800 times dilution， and 40% edifenphos EC 800-1 000 times dilution， which can be sprayed once every 10 d  [7] .

Maize southern leaf blight

Maize southern leaf blight can occur from the seedling stage to the mature stage， and it mainly damages the leaves， but the bracts and seeds of the stems and ears can also be damaged.  Leaf lesions are small and numerous， initially small brown watery spots， and then expand into oval or rectangular lesions of about  0.5  cm， with purple or red halo circles on the edges. The lesions on leaf sheaths and ear bracts are generally spindle-shaped or irregular， yellowish-brown， with purple-black or inconspicuous edges， and the diseased parts are often densely covered with a layer of gray-black mold， which sometimes causes the ears to rot or droop and fall off and the seeds to turn black. Southern leaf blight mainly damages leaves and stems， and oval or rectangular spots appear during the onset， which can be prevented and eradicated by diluting and spraying with azoxystrobin  [8] .

Occurrence regularity

The disease is caused by fungi， and the pathogens are fungi of Deuteromycotina. The pathogens overwinter on the disease plant residues and are the sources of primary infection. They spread by wind， rain and air flow for initial infection  and re-infection. The optimum temperature for onset is 26-29 ℃.  In case of sufficient water or high humidity conditions， the disease spreads rapidly. During the booting and heading stages of maize， the weather conditions are a lot of rainfall and high humidity， which is easy to cause the prevalence of southern leaf blight.

Prevention and control strategy

Seed treatment： Seed coating agents are medicine and fertilizer compounded seed treatment  agents，  which are prepared from pesticides， microbicides， compound fertilizers， trace elements， plant growth regulators， slow-release agents and film-forming agents. They have the functions of preventing seed-borne microbes and seedling diseases. Seed-carrying microbes are one of the primary infection sources of southern leaf blight. Treating parental seeds using the seed coating technology can effectively reduce the primary infection sources of southern leaf blight and has a certain effect in controlling the occurrence of southern leaf blight.

① Agricultural prevention and control： The diseased fields should be turned in autumn， so that the diseased plant residues are buried 10 cm below the surface of the ground. It is necessary to remove the residues of diseased plants on the ground， and fully decompose fungus-carrying residues. Seeds should be sown at the right time to avoid rainy weather during the heading stage. Sufficient base fertilizer should be applied， and top dressing should be carried out in an appropriate period at an appropriate rate， to ensure the nutritional supply of the female parent throughout the period， and to promote robust plant growth. Especially the nutritional supply from the jointing to flowering stage must be guaranteed.

② Chemical control： On the basis of agricultural control and seed coating， 750 g of 50% Haosujing WP， or 900 g of 80% sancozeb WP is applied per hectare for 3 times. Agents can also be sprayed at the early stage of the disease. Commonly used agents also include 75% chlorothalonil WP 300 times dilution and 70% thiophanate-methyl WP 600 times dilution once every 7-10 d， continuously for 2-3 times in total.

Maize rust

Maize rust mainly affects leaves， and can also occur on ear husks and male flowers in severe cases. The middle and upper leaves of the plants are seriously affected， initially scattered or clustered on the front of the leaves with inconspicuous pale yellow spots， which later protrude， and expanded into round to oblong， and are yellowish-brown or brown. Then， the surrounding epidermis turns up， and rust powder （uredospores of the pathogen） is dispersed. In the later stage， round black protrusions grow on the lesions， and after rupture， black-brown powder （pathogen teliospores） is exposed. The rust disease mainly damages the leaves. Circular lesions appear on the leaves in the early stage of the disease， accompanied by rust-colored powder， and spores will grow on the lesions in the later stage. These spores can safely overwinter， and will re-infect the leaves by air currents in the following year， and gradually expand， which is extremely harmful. When selecting seeds， hybrid varieties with strong disease resistance can be selected， and fertilizers should be applied reasonably. In the early stage of the disease， triadimefon wettable powder is diluted and sprayed， and it can be sprayed repeatedly when the disease is severe.

Occurrence regularity

The disease is caused by fungi which belong to Basidiomycotina and spread in the south with uredospores. In the north， the sources of fungi are mainly diseased bodies or uredospores from the south and the alternate host，  Oxalis corniculata  L.， which become the initial infection sources of the disease. After the leaves have been diseased in the field， the spores produced by the diseased parts are spread by air flow， perform re-infection and spread. In production， early-maturing varieties are prone to disease， and the application of excessive nitrogen fertilizer makes the disease severe. High temperature， high humidity， rainy， foggy days and insufficient light are conducive to the prevalence of maize rust.

Prevention and control strategy

Agricultural control： Disease-resistant varieties can be selected， and dent-type varieties with a long growth period can be selected. Fertilizers should be applied reasonably according to the type of fertilizers required for maize， and attention should be paid to the application of micro-fertilizers  such as phosphorus and potassium fertilizers. It is necessary to increase the application of phosphorus and potassium fertilizers and   avoid  partial application and heavy application of nitrogen fertilizers，  so as to improve host disease resistance. Field management should be strengthened， and  O. corniculata  and diseased residues should be removed by deeply burying or burning them to reduce the sources of infection.

Chemical control： Spraying of agents is started in the early stage of the disease， and commonly used agents are 25% triazolone WP 1 500-2 000 times dilution， 50% sulfur suspension agent 300 times dilution， 30% solid lime sulphur 150 times dilution， 25% propiconazole emulsified oil 3 000 times dilution， and 12.5 dinconazole wettable powder 4 000-5 000 times dilution. The spraying is performed once every 10 d or so for 2-3 times continuously.

Maize head smut

Maize head smut， also known as black ear and dumb corn， is an important disease in spring maize areas in China. It mainly affects ears and tassels of maize. It mostly show symptoms after ear emergence， but some inbred lines show symptoms at the seedling stage， with 1-4 yellow-white stripes on 4-5 leaves. For diseased tassels， sometimes whole inflorescences are destroyed and blackened， and the glumes increase and lengthen. Diseased ears are shorter than healthy ears， and show enlarged lower parts and sharper tops， and the whole ears become a mass of dark brown powder and many scattered black filaments.

Occurrence regularity

The disease is caused by a fungus that becomes a source of infection early in the following year on soil， manure or seeds. When maize seeds germinate after sowing， the  overwintering  chlamydospores also begin to germinate. They can invade from the white tip stage to the 4-leaf stage of maize， and reach the growth point. As the maize plant grows and develops， the fungus enters flower buds and ears， forming a large amount of black powder， and the ears become black and have black filaments thereon. The incidence is severe in fields with a long continuous cropping period and in maize sown early. High， cold and cool plots are prone to disease. The incidence is light in fields with sandy loam. The incidence is light in dry land with good moisture condition， but severe in that with poor moisture condition. The infection temperature limit is 15-35 ℃， and the optimum infection temperature is 20-30 ℃.

Susceptible varieties are one of the factors leading to the serious occurrence of head smut. The pathogenic fungus can appear new physiological races， resulting in the loss of resistance in the original resistant varieties. Early sowing and the low temperature after seed germination create suitable environmental conditions for the disease to occur. Continuous cropping of maize for many years results in the accumulation of a large number of pathogenic fungi in the field， which is conducive to the occurrence of maize head smut. Diseased plants that are not removed， fungus-carrying manure applied to the field， small investment and extensive management are all the reasons for disease occurrence.

Agricultural Biotechnology 2022

Prevention and control strategy

① Seed treatment： Seed coating agents with disease prevention effects can be promoted in areas with severe head smut disease. The seed coating agents for the control of maize head smut mainly contain tebuconazole， dinconazole， triazolone and other seed coating agents， but the seed coating agents containing tebuconazole have the best control effect and the highest safety. Dinconazole produces phytotoxicity when the sowing depth exceeds 3 cm under low temperature conditions. Triadimenol and triadimefon have a certain inhibitory effect on maize seedling stage， and there is a potential safety hazard. In contrast， tebuconazole not only has good control effect and high safety， but also the effects of promoting plant growth， developing root system， increasing effective tillering， increasing yield， and accelerating germination. Therefore， to prevent maize head smut， seed coating agents containing tebuconazole should be the first choice.

② Agricultural control： Varieties with good resistance to head smut can be actively promoted. Some varieties have stable disease resistance. Even in the years when the disease occurs seriously， the incidence of these varieties is generally lower than 10%， such as Nongda 108， Nongda 313， Benyu No. 9， Jidan 180， Sidan 19 and Xintiedan 10. It is necessary to eliminate the sources of initial infection， clean the field， remove diseased plants， and deal with diseased tissues. Manure should be fully decomposed. In severely diseased fields， after the flowering period of maize， once diseased plants are found， they must be cut off and buried deep to prevent the spread of germs. Even if intercropping rotation is not performed， intervarietal rotation should be performed when selecting maize varieties.

Maize sheath blight

Maize sheath blight mainly damages leaf sheaths， but also stems， and damages ears in severe cases. In the early stage of the disease， dark green watery lesions usually appear on the sheaths of 1-2 stem nodes at the base， and then expand to form large irregular or moiré lesions. The lesions have a gray-brown center， with dark brown edges. The same moiré spots are also produced in the infestation of ear bracts. After the onset in ears， ear tips are bald， and the seeds are thin and flat or brown and rotten. In severe cases， the rhizome tissues become gray-white， and the secondary roots are yellow-brown or rotten. When it is rainy and high humidity for a long time， the diseased parts give off dense white mycelia， and the mycelia further aggregate into multiple mycelium clusters to form small microsclerotia.

Occurrence regularity

The disease is caused by a fungus， and the causative fungus is the fungus  R. solani  of Deuteromycotina. Pathogens overwinter in diseased residues or soil， and overwintering sclerotia and diseased bodies scattered in the field and under-decomposed maize stalks used as fertilizers， are the primary infection sources of maize sheath blight. The pathogen germinates when conditions are favorable in spring to cause disease， and reinfection happens by contact with neighboring plants. Too dense planting， too much nitrogen application， high humidity， and continuous rain can cause the disease easily. The main disease stage is from the formation of maize sex organs to the filling stage， and the disease is milder at the seedling stage and later growth stage  [9] .

Prevention and control strategy

Seed treatment： After seed dressing with Jinzhongling 0.02% of seed weight， the seeds are piled for 24-48 h.

Agricultural control： Diseased residues and sclerotia are removed. In the early stage of the disease， the diseased leaves are removed， and the diseased parts such as leaf sheaths are smeared with drugs. It is necessary to implement crop rotation， plant reasonably densely， pay attention to ditching and drainage， reduce field humidity， and combine cultivating to eliminate field weeds.

Chemical control： The tasseling period is the best control period. Commonly used agents include 1% jinggangmycin 0.5 kg in mixture with 200 kg of water， 50% thiophanate-methyl WP 500 times dilution， 50% carbendazim WP 600 times dilution， 50% benomyl WP 1 500 times dilution， 50% tuzet WP 800-1 000 times dilution， 40% ezomycin WP 1 000 times dilution， 50% vinclozolin or 50% procymidone WP 1 000-2 000 times dilution. The focus of spraying is on the base of maize and protects leaf sheaths.

Curvularia lunata  （Walk） Boed

C. lunata  is another new leaf disease after maize northern leaf blight and maize southern leaf blight， and it occurs widely in all major maize producing areas in China.

Occurrence regularity

The disease mainly damages leaves， and sometimes leaves sheaths and bracts. Small chlorotic spots appear in the early stage of the disease， and gradually expand into circular chlorotic and transparent spots， which are withered white to yellowish brown in the middle， dark brown at the edges， and have  light yellow halo around. The size is （0.5-4.0） mm×（0.5-2.0）  mm. When the humidity is high， gray powder can be seen on the front and back of the lesions， and mostly on the back. The disease is caused by a fungus，  C. lunata  of Deuteromycotina.

Prevention strategy

Agricultural control： Attention should be paid to rational layout and rotation among varieties. Maize stalks and diseased residues on the field surface are the main sources of primary infection of  C. lunata . The stalks can be directly returned to the field， composted at high temperature， put in livestock pens or used for firewood. It is necessary to avoid using the stalks for building a fence， and maize stalks should not be left on the edge of villages or on the ground to reduce the sources of initial infection. In addition， returning stalks to the field can also improve soil structure， increase soil fertilizer and reduce the sources of primary infection fungus. Moreover， straw returning can also improve soil structure and increase soil fertility. Timely and early sowing， reasonable dense planting， and intercropping with medium-to-short stalk crops can create environmental conditions that are conducive to the growth of maize but not conducive to the occurrence and development of diseases， and can reduce the degree of disease occurrence.

Chemical control： Tuzet has a strong inhibitory effect on the germination of conidia and mycelial growth of  C. lunata ， and the disease prevention effect in the field experiment is also very good. Therefore， in the production process， tuzet can be used as the first-choice agent for the prevention and control of  C. lunata . Mancozeb and chlorothalonil have strong inhibitory effects on conidial germination of pathogens， but weak inhibitory effects on mycelial growth， so they can be used as protective agents in the early stage of the disease in production. Polysulfide mixture， thiophanate-methyl， and carbendazim have strong inhibitory effects on the growth of pathogen mycelia， but weaker inhibitory effects on the germination of pathogen conidia， so they can be used as therapeutic agents.  The use of protective agents and therapeutic agents alternately or in combination can not only improve the control effect， but also prevent fungi from developing resistance to a single agent.

Fusarium avenaceum  （Fr.） Sacc.

This disease is mainly manifested as ear infection. The ends of ear turn purple-red， and sometimes there are pink to gray-white mycelia between grains. The diseased grains are tarnished， not full. The germination rate is reduced， and the seeds are easy to rot after sowing. In addition to infecting maize， it can also infect wheat， barley， oats， rice， millet and other gramineous plants.

Occurrence regularity

Seedlings grow abnormally with yellow leaves in light cases. Sometimes there are symptoms of stem rot， with which the stems are partially brown and have purple pith， and they are easy to collapse. Leaf sheaths are infected with orange punctate sticky conidia. The fungus is easy to grow and multiply in the wounds or grooves after maize growth laceration， mechanical damage， and insect and bird damage. The disease is probability to occur at the temperature of 18-20 ℃ and the relative humidity of 95%-98% in the air. The incidence in summer maize is more serious in the conditions of early drought， rain in the middle and high temperature at later stages. High-lysine maize is susceptible to the disease. The incidence is relatively serious in susceptible varieties which are planted with high density and straw returning to the field， and in low-lying land.

Prevention and control strategy

Disease-resistant maize varieties can be chosen according to local conditions， and the farming system should be improved. The sowing period should be properly adjusted， so that the peak period of the disease， that is， the booting to heading stage of maize， does not meet the rainy season as much as possible. Field management is strengthened. Phosphorus and potassium fertilizers are applied at the jointing or booting stage of maize in combination with nitrogen fertilizers to enhance plant disease resistance. After the onset of the disease， attention should be paid to ditching and drainage to prevent moisture retention. If necessary， 5% jinggangmycin water agent is sprayed on the ears， at 750-1 125 ml/hm 2 in mixture with 1 125-1 500 L of water， or 50% thiophanate-methyl wettable powder 600 times dilution， 50% carbendazim suspension 700-800 times dilution， 50% benomyl WP 1 500 times dilution and 40% vinclozolin WP 1 000 times dilution can be used. The disease is controlled 1 or 2 times depending on the disease condition.

Prevention and Control Methods 

Biological control

Biological control mainly uses the method of overcoming the enemy with the enemy to eliminate pests and diseases. From the perspective of environmental protection， biological control technology has great advantages.

Physical control

The best method of pest control is physical control， which can reduce environmental pollution and effectively eliminate pests. The disadvantage of physical control is that the investment is relatively large， which will bring a certain burden to farmers. It is more suitable for large-scale maize production bases.

Chemical control

Chemical control is mainly spraying agrochemicals， which is a commonly used method for eliminating pests by maize growers in Henan Province. It is mainly to prepared different agrochemicals proportionally in different periods of maize growth to control pests and diseases， but this method will cause agrochemical residues in the fields and rivers， which will result in adverse effects on the environment.

Strengthen market management

Strengthening market management can prevent the sales of fake seeds， reduce the sales of fake fertilizers and agrochemicals， crack down on illegal behaviors， and protect the economic interests of farmers from losses.

Prevention and control measures of maize diseases and pests in various growth stages 

Prevention and control measures before sowing

The main thing is to choose good disease-resistant varieties， while avoiding large-scale planting of one variety. During land preparation， deep ploughing and stubble removal are required to eliminate the sources of pests and diseases. Weeds from the field and the edge of the ground should be removed to cut off the parasitic bridges of pests and diseases.

Prevention and control measures during the sowing period

In this period， the main task is to control underground pests and seed-borne diseases. The seeds can be coated with chemicals according to local conditions， and the summer direct seeding technology can be adopted to implement the rotation of maize， cotton and vegetables.

Prevention and control measures after sowing before emergence

At this stage， it is necessary to take the initiative to prevent diseases and pests. Chemicals can be sprayed after sowing and before emergence， while paying attention to keep the soil in the field flat. If the field is dry before spraying， it should be  watered  first， and then， agrochemicals can be sprayed after about  3 d.

Control measures at the seedling stage

At the seedling stage， the main task is to control underground pests， strengthen the management of fertilizer and water in the field， and use formula fertilizers to cultivate robust plants to enhance resistance. Intertillage and weeding should be carried out to cut off the parasitic bridges of pests. Combining with the characteristics of stable seedlings and different resistance to diseases and pests at different states during the growth process of maize， weak and small diseased seedlings are timely removed， and chemical weeding is carried out in time. Plants seriously affected by pests and diseases should be removed in time to avoid the spread of pests and diseases.

Control measures at the ear stage

There are many diseases and pests at this stage. It is necessary to strengthen water and fertilizer management and increase the application amount of phosphorus and potassium fertilizers to improve the ability of plants to resist diseases and pests.

Preventive measures during the filling stage

During this period， field management should be strengthened， the ventilation conditions of maize should be improved， and the quality of pollination， fertilization and grain filling should be improved.

Control measures after harvesting

After maize is harvested， diseased plants in the field should be removed in time and destroyed in a centralized manner to eliminate the source of pathogens. Meanwhile， the fields should be deeply ploughed to eliminate winter pests. Maize stalks and cobs should be thoroughly disposed before maize borer pupation in spring to eliminate overwintering maize borer larvae. After harvesting， the ears of maize should not be stacked too thick to prevent them from being exposed to rain and damp. After maize is harvested， the husks should be peeled off in time and dried in a ventilated place to prevent the occurrence of the disease due to heat. The ears are threshed as soon as possible after drying.

Conclusions

Maize occupies an important position in China’s agricultural economy， and the problem of maize diseases and pests seriously affects the yield and quality of maize. In the process of maize planting， the primary prerequisite for pest control is to first understand pests and diseases， and then carry out comprehensive control from multiple perspectives. Under the premise of effectively protecting the environment， planting technologies and physical， chemical and biological pest control methods should be used to control pests and diseases in all aspects of maize growth， so as to improve maize yield and quality and increase farmers’ income  [10] . This paper summarized the occurrence status of important maize diseases in China， and analyzed the occurrence trend. The soil-borne diseases such as stem rot and ear rot will continue to increase. Risky leaf spot diseases such as maize northern leaf blight and southern rust are still prevalent and cannot be ignored in the future. Through the introduction of the identification and prevention methods of common maize diseases， we can popularize professional technical knowledge to farmers， benefit more farmers， ensure the yield and quality of maize while ensuring the economic benefits of farmers， and reduce farmers’ losses.

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 Editor： Yingzhi GUANG   Proofreader： Xinxiu ZHU