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Abstract The occurrence of maize diseases was systematically studied at different growth stages of maize in different areas of Anhui Province. It was found that maize has a long optimal growth period in Anhui Province， and the maize planting structure is complex. The northern region is mainly planted with summer maize in large scale， while the southern region is mainly planted with spring maize in scattered pattern. In terms of diseases， the south spring maize suffered from more diverse diseases than the north summer maize. The main maize disease in Suzhou， Bozhou， Fuyang and Bengbu areas was southern rust， which was common with the highest diseased plant rate of 76%. The main maize diseases in Luюan， Anqing， Chizhou， Tongling and Xuancheng were rust， maize rough dwarf virus （MRDV）， southern leaf blight and sheath blight. Other diseases such as northern leaf blight， stalk rot and maize smut occurred commonly. The diseased plant rate of maize rust was in the range of 25%-47%.
Key words Anhui Province; Maize; Disease; Investigation
With the rapid development of Chinaюs maize processing industry and animal husbandry， maize as an important feed， an industrial raw material and a food crop， its important position has become increasingly prominent， and it has now become Chinaюs largest food crop. Anhui is located in the central region of East China， and has a warm temperate semihumid climate with abundant sunshine， abundant heat， abundant rainfall， simultaneous rain and heat， large temperature difference between day and night in spring and autumn， and these ecological conditions are very suitable for the growth of summer maize. It is one of the main maize producing areas in the Huang-Huai-Hai Plain， and has a high potential of high yield[1-2].
In 2010， the planting area of maize in the province increased from 2.33≠105 hm2 in 1978 to 7.78≠105 hm2. Especially since 2014， the provinceюs maize planting area has expanded to 8.87≠105 hm2， and the output has increased from 3.8≠108 to 3.05≠109 kg. As a result， Anhui Province has entered the ranks of the countryюs major maize production provinces. However， due to the lack of mature key techniques and insufficient integration and promotion of advanced methods， the average yield of maize per unit area in our province is around 4 500 kg/hm2， which is far lower than the national level and those of surrounding provinces and cities. Furthermore， the problem of pests and diseases has always been one of important factors influencing stable and high yield of maize[3]. Anhui Province has diverse climatic conditions， and the planting structure is complex. There are many types of maize pests， which also differ in occurrence characteristic and harm stage. Exploring the harm law of maize pests in Anhui Province is of great significance to the formulation of pest control strategies according to local conditions. For this purpose， a systematic regional investigation was conducted on occurrence of major maize diseases in Anhui Province in 2016-2017， so as to analyze the main types and occurrence degree of maize diseases in various areas of Anhui Province at different stages. This study lays a foundation for rational layout of control measures.
Materials and Methods
Investigation on main diseases of south spring maize in Anhui Province
Investigation areas： Luюan， Anqing， Chizhou， Tongling and Xuancheng.
The occurrence of summer maize diseases was investigated in Anhui Province at the seedling and ear stages of spring maize. Three representative townships/towns were selected in each area， and three villages were selected from each township/town. And in each selected village， three representative maize fields were selected for sampling. During sampling in each field， samples were collected by the double diagonal method of five points at each of which 20 maize plants were investigated randomly， which meant that 100 maize plants were investigated in each field. All diseases in the maize fields were recorded.
Investigation on main diseases of north summer maize in Anhui Province
Investigation areas： Suzhou， Bozhou， Fuyang and Bengbu.
The occurrence of summer maize diseases was investigated in Anhui Province at the seedling and ear stages of summer maize. The investigation method was the same as "Investigation on main diseases of south spring maize in Anhui Province".
Results and Analysis
Investigation on main diseases of south spring maize in Anhui Province
Many kinds of pests were observed on south spring maize. The seedling diseases mainly included maize Curvularia leaf spot disease， maize southern and northern leaf blight， maize sheath blight， maize rough dwarf virus （MRDV）， maize bacterial stalk rot and maize mosaic virus disease. Maize mosaic virus disease was observed in partial areas， and in some areas such as Shucheng， maize bacterial stalk rot was observed （Table 1）. It was found from the investigation that the maize pests and diseases in the spring maize seedlings were the most serious in Tongling， where the damage rate was 56% for the rust disease in rust disease investigation in July， and was 6% for sheath blight， and the scab was also observed with a damage rate of 4%. The diseases were the second serious in Xuancheng area， and the lightest in Luюan area and Anqing area. In addition， some minor diseases occurred severely in some areas. For instance， the MRDV was serious in spring maize in Tongling area， with a damage rate of 100 plants of 12.6%， and the maize northern and southern leaf blight showed a damage rate of 100 plants reaching 24.8%. The maize Curvularia leaf spot disease， maize southern leaf blight， maize northern leaf blight and maize sheath blight were also more serious in spring maize at seedling stage， and the damage rate of 100 plants in spring maize was 17.6% at the seedling and ear stages averagely.
Investigation on main diseases of north summer maize in Anhui Province
At seedling stage， the diseases in north summer maize mainly included MRDV， maize dwarf mosaic disease， maize southern leaf blight and brown spot disease. Among them， the Xiaoxian area of Suzhou showed the highest damage rate of maize southern leaf blight at seedling stage， which was 45%， followed by Fuyang area， which exhibited a damage rate of 11.6%. MRDV was serious in Fuyang area occasionally at seedling stage， and some of the fields had the highest MRDV damage rate of 100 plants of 30%. Maize dwarf mosaic disease was observed in Bengbu area occasionally， and the damage rate of 100 plants was 0.9%.
At ear stage， the main diseases in the summer maize were maize northern and southern leaf blight， sheath blight， maize smut， maize bacterial stalk rot and maize rust. The damage caused by leaf spot disease decreased， while the damage of maize rust was widespread and aggravated; and sheath blight was common along the Huaihe River. Specifically， maize rust commonly occurred in Fuyang area， and the damage rate of 100 plants was the highest of 76.7%， and reached 100% in some fields; Suzhou area had the second highest damage rate of 100 plants， of 68%; and the disease was the lightest in Bengbu area， where the damage rate of 100 plants still reached 45% （Table 2）. In the fields with later growth stages， the maize smut disease harmed the female ear. For instance， in Sunweizi of Suzhou City， and the damage rate of maize smut was 1.5%. The mixed damage of maize bacterial stalk rot and sheath blight occurred occasionally. For instance， in a field in Fuli Town， Suzhou City， the bacterial stalk rot showed a damage rate of 100 plants of 3.2%， accompanied by sheath blight.
Discussion
Anhui Province belongs to the transition zone of the warm temperate zone and subtropical zone， where has a long optimal growth period. Previous investigations show that maize grows in Anhui Province from March to November. In the Dongzhi area of Chizhou City， special maize has already been sown in midlate February， while in midlate November of the very year， latematuring varieties in some fields have not yet been harvested. Meanwhile， Anhui Province spans the Yangtze River and the Huaihe River， and has complex planting structure， and the maize planting patterns are diverse. In Huaibei and Jianghuai areas， as the main maize producing area of Anhui Province， summer maize is mainly planted， and spring maize is planted in some areas. For instance， in Xiaoxian County， Suzhou City， spring maize is planted in April， so as to meet the cultivation time of carrots; and in southern hilly spring maize planting area， maize， mainly special spring maize， is planted in scattered pattern mostly， sporadically around fields and behind the farmhouse. These climatic characteristics and planting methods provide the possibility of the occurrence， development and transfer of a variety of maize pests and diseases. In Anhui Province， whether for spring maize or summer maize， it was found from the growth period investigation that the maize northern and southern leaf sheath was common in various maize producing areas in Anhui Province. The maize northern and southern leaf sheath occurs in the growing period of maize and does not affect the growth and yield of maize in late period， so this disease is basically not regarded as a control object.
It was found from this investigation that certain diseases such as maize stalk rot were severe in some areas. The maize rust seriously harmed summer maize in Anhui Province at ear stage， and in some fields in Fuyang City， the damage rate of 100 plants reached 100% in summer maize at ear stage. Maize leaves， stalks and bracts all might be damaged. Maize rust mainly harms maize leaves and leaf sheaths， and also infects stalks and bracts in severe case， and as a result， the plants are covered with disease spots which inhibit photosynthesis， resulting in reduced quality and decreased yield. There is an urgent need to screen and promote highefficiency agents and control methods.
In recent years， the maize producing area in Anhui Province has been continuously expanded， and the situation of pests and diseases is complex. The understanding of the law of disease occurrence is of great significance to the screening of highefficiency agents， formulation of reasonable control strategies and improvement of the prevention and control level.
References
[1]CHEN HJ， LI XZ. The climate characteristics of Huaibei and summer maize cultivation[J]. Journal of Anhui Agricultural Sciences， 1995， 23（1）： 49-511. （in Chinese）
[2]CAO CF， XU SQ， WANG ZS. Study on yield potential and matching techniques of summer maize in Shajiang black soil area[J]. Journal of Anhui Agricultural Sciences， 1999， 27（1）： 17-191. （in Chinese）
[3]HAUNG YS. Studies on succession law and divisions of maize plant diseases and insect pests of the major maize producing areas in Anhui Province[D]. Hefei： Anhui Agricultural University， 2013. （in Chinese）
[4]DONG M， TAN GJ， WANG XY， et al. Field investigation and maize pathogen identification in Anhui Province[J]. Journal of Anhui Agricultural University， 2010， 37（3）： 429-435. （in Chinese）
[5]GAO ZG， CHEN J， XUE CS， et al. Study on incidence， regularity of epidemiology and inducing condition of gray leaf spot in maize[J]. Journal of Shenyang Aricultural University， 2000，31（5）：460-464. （in Chinese）
[6]JI ZF， WANG AL， LI JX， et al. Relationship between the occurrence of maize rough dwarf virus disease and sowing date and variety[J]. Plant Protection， 1998， 24（4）： 27-29. （in Chinese）
[7]MIAO HQ， CHEN X. Harm and prevention of maize rough dwarf virus disease in Hebei Province[J]. Plant Protection，1997，23（6）：17-18. （in Chinese）
[8]WANG XM， DAI FX， LIAO Q， et al. Field manual of maize pests and diseases[M]. Beijing： China Agriculture Science and Technique Press， 2002. （in Chinese）
[9]CHENG ZB， ZHOU YJ， FAN YJ， et al. Epidemic regularity， damage and causes of maize rough dwarf virus disease in Sheyang， Jiangsu province[J]. Jiangsu Agricultural Sciences， 1998， 3（1）： 32-35. （in Chinese）
Key words Anhui Province; Maize; Disease; Investigation
With the rapid development of Chinaюs maize processing industry and animal husbandry， maize as an important feed， an industrial raw material and a food crop， its important position has become increasingly prominent， and it has now become Chinaюs largest food crop. Anhui is located in the central region of East China， and has a warm temperate semihumid climate with abundant sunshine， abundant heat， abundant rainfall， simultaneous rain and heat， large temperature difference between day and night in spring and autumn， and these ecological conditions are very suitable for the growth of summer maize. It is one of the main maize producing areas in the Huang-Huai-Hai Plain， and has a high potential of high yield[1-2].
In 2010， the planting area of maize in the province increased from 2.33≠105 hm2 in 1978 to 7.78≠105 hm2. Especially since 2014， the provinceюs maize planting area has expanded to 8.87≠105 hm2， and the output has increased from 3.8≠108 to 3.05≠109 kg. As a result， Anhui Province has entered the ranks of the countryюs major maize production provinces. However， due to the lack of mature key techniques and insufficient integration and promotion of advanced methods， the average yield of maize per unit area in our province is around 4 500 kg/hm2， which is far lower than the national level and those of surrounding provinces and cities. Furthermore， the problem of pests and diseases has always been one of important factors influencing stable and high yield of maize[3]. Anhui Province has diverse climatic conditions， and the planting structure is complex. There are many types of maize pests， which also differ in occurrence characteristic and harm stage. Exploring the harm law of maize pests in Anhui Province is of great significance to the formulation of pest control strategies according to local conditions. For this purpose， a systematic regional investigation was conducted on occurrence of major maize diseases in Anhui Province in 2016-2017， so as to analyze the main types and occurrence degree of maize diseases in various areas of Anhui Province at different stages. This study lays a foundation for rational layout of control measures.
Materials and Methods
Investigation on main diseases of south spring maize in Anhui Province
Investigation areas： Luюan， Anqing， Chizhou， Tongling and Xuancheng.
The occurrence of summer maize diseases was investigated in Anhui Province at the seedling and ear stages of spring maize. Three representative townships/towns were selected in each area， and three villages were selected from each township/town. And in each selected village， three representative maize fields were selected for sampling. During sampling in each field， samples were collected by the double diagonal method of five points at each of which 20 maize plants were investigated randomly， which meant that 100 maize plants were investigated in each field. All diseases in the maize fields were recorded.
Investigation on main diseases of north summer maize in Anhui Province
Investigation areas： Suzhou， Bozhou， Fuyang and Bengbu.
The occurrence of summer maize diseases was investigated in Anhui Province at the seedling and ear stages of summer maize. The investigation method was the same as "Investigation on main diseases of south spring maize in Anhui Province".
Results and Analysis
Investigation on main diseases of south spring maize in Anhui Province
Many kinds of pests were observed on south spring maize. The seedling diseases mainly included maize Curvularia leaf spot disease， maize southern and northern leaf blight， maize sheath blight， maize rough dwarf virus （MRDV）， maize bacterial stalk rot and maize mosaic virus disease. Maize mosaic virus disease was observed in partial areas， and in some areas such as Shucheng， maize bacterial stalk rot was observed （Table 1）. It was found from the investigation that the maize pests and diseases in the spring maize seedlings were the most serious in Tongling， where the damage rate was 56% for the rust disease in rust disease investigation in July， and was 6% for sheath blight， and the scab was also observed with a damage rate of 4%. The diseases were the second serious in Xuancheng area， and the lightest in Luюan area and Anqing area. In addition， some minor diseases occurred severely in some areas. For instance， the MRDV was serious in spring maize in Tongling area， with a damage rate of 100 plants of 12.6%， and the maize northern and southern leaf blight showed a damage rate of 100 plants reaching 24.8%. The maize Curvularia leaf spot disease， maize southern leaf blight， maize northern leaf blight and maize sheath blight were also more serious in spring maize at seedling stage， and the damage rate of 100 plants in spring maize was 17.6% at the seedling and ear stages averagely.
Investigation on main diseases of north summer maize in Anhui Province
At seedling stage， the diseases in north summer maize mainly included MRDV， maize dwarf mosaic disease， maize southern leaf blight and brown spot disease. Among them， the Xiaoxian area of Suzhou showed the highest damage rate of maize southern leaf blight at seedling stage， which was 45%， followed by Fuyang area， which exhibited a damage rate of 11.6%. MRDV was serious in Fuyang area occasionally at seedling stage， and some of the fields had the highest MRDV damage rate of 100 plants of 30%. Maize dwarf mosaic disease was observed in Bengbu area occasionally， and the damage rate of 100 plants was 0.9%.
At ear stage， the main diseases in the summer maize were maize northern and southern leaf blight， sheath blight， maize smut， maize bacterial stalk rot and maize rust. The damage caused by leaf spot disease decreased， while the damage of maize rust was widespread and aggravated; and sheath blight was common along the Huaihe River. Specifically， maize rust commonly occurred in Fuyang area， and the damage rate of 100 plants was the highest of 76.7%， and reached 100% in some fields; Suzhou area had the second highest damage rate of 100 plants， of 68%; and the disease was the lightest in Bengbu area， where the damage rate of 100 plants still reached 45% （Table 2）. In the fields with later growth stages， the maize smut disease harmed the female ear. For instance， in Sunweizi of Suzhou City， and the damage rate of maize smut was 1.5%. The mixed damage of maize bacterial stalk rot and sheath blight occurred occasionally. For instance， in a field in Fuli Town， Suzhou City， the bacterial stalk rot showed a damage rate of 100 plants of 3.2%， accompanied by sheath blight.
Discussion
Anhui Province belongs to the transition zone of the warm temperate zone and subtropical zone， where has a long optimal growth period. Previous investigations show that maize grows in Anhui Province from March to November. In the Dongzhi area of Chizhou City， special maize has already been sown in midlate February， while in midlate November of the very year， latematuring varieties in some fields have not yet been harvested. Meanwhile， Anhui Province spans the Yangtze River and the Huaihe River， and has complex planting structure， and the maize planting patterns are diverse. In Huaibei and Jianghuai areas， as the main maize producing area of Anhui Province， summer maize is mainly planted， and spring maize is planted in some areas. For instance， in Xiaoxian County， Suzhou City， spring maize is planted in April， so as to meet the cultivation time of carrots; and in southern hilly spring maize planting area， maize， mainly special spring maize， is planted in scattered pattern mostly， sporadically around fields and behind the farmhouse. These climatic characteristics and planting methods provide the possibility of the occurrence， development and transfer of a variety of maize pests and diseases. In Anhui Province， whether for spring maize or summer maize， it was found from the growth period investigation that the maize northern and southern leaf sheath was common in various maize producing areas in Anhui Province. The maize northern and southern leaf sheath occurs in the growing period of maize and does not affect the growth and yield of maize in late period， so this disease is basically not regarded as a control object.
It was found from this investigation that certain diseases such as maize stalk rot were severe in some areas. The maize rust seriously harmed summer maize in Anhui Province at ear stage， and in some fields in Fuyang City， the damage rate of 100 plants reached 100% in summer maize at ear stage. Maize leaves， stalks and bracts all might be damaged. Maize rust mainly harms maize leaves and leaf sheaths， and also infects stalks and bracts in severe case， and as a result， the plants are covered with disease spots which inhibit photosynthesis， resulting in reduced quality and decreased yield. There is an urgent need to screen and promote highefficiency agents and control methods.
In recent years， the maize producing area in Anhui Province has been continuously expanded， and the situation of pests and diseases is complex. The understanding of the law of disease occurrence is of great significance to the screening of highefficiency agents， formulation of reasonable control strategies and improvement of the prevention and control level.
References
[1]CHEN HJ， LI XZ. The climate characteristics of Huaibei and summer maize cultivation[J]. Journal of Anhui Agricultural Sciences， 1995， 23（1）： 49-511. （in Chinese）
[2]CAO CF， XU SQ， WANG ZS. Study on yield potential and matching techniques of summer maize in Shajiang black soil area[J]. Journal of Anhui Agricultural Sciences， 1999， 27（1）： 17-191. （in Chinese）
[3]HAUNG YS. Studies on succession law and divisions of maize plant diseases and insect pests of the major maize producing areas in Anhui Province[D]. Hefei： Anhui Agricultural University， 2013. （in Chinese）
[4]DONG M， TAN GJ， WANG XY， et al. Field investigation and maize pathogen identification in Anhui Province[J]. Journal of Anhui Agricultural University， 2010， 37（3）： 429-435. （in Chinese）
[5]GAO ZG， CHEN J， XUE CS， et al. Study on incidence， regularity of epidemiology and inducing condition of gray leaf spot in maize[J]. Journal of Shenyang Aricultural University， 2000，31（5）：460-464. （in Chinese）
[6]JI ZF， WANG AL， LI JX， et al. Relationship between the occurrence of maize rough dwarf virus disease and sowing date and variety[J]. Plant Protection， 1998， 24（4）： 27-29. （in Chinese）
[7]MIAO HQ， CHEN X. Harm and prevention of maize rough dwarf virus disease in Hebei Province[J]. Plant Protection，1997，23（6）：17-18. （in Chinese）
[8]WANG XM， DAI FX， LIAO Q， et al. Field manual of maize pests and diseases[M]. Beijing： China Agriculture Science and Technique Press， 2002. （in Chinese）
[9]CHENG ZB， ZHOU YJ， FAN YJ， et al. Epidemic regularity， damage and causes of maize rough dwarf virus disease in Sheyang， Jiangsu province[J]. Jiangsu Agricultural Sciences， 1998， 3（1）： 32-35. （in Chinese）