Control techniques of maize diseases and insect pests

Corn is often harmed by all kinds of diseases and insects in the process of production, and its yield is seriously reduced. For example, in the epidemic years of leaf spot disease, the yield can be reduced by 15Mu30% due to the disease, and by more than 50% in seriously diseased fields; the harm of corn borer usually reduces corn production by about 10%, and by about 30% in serious years. There are many kinds of diseases and insect pests that harm corn, including large leaf spot, small leaf spot, head smut, bacterial wilt, ear rot and virus disease. in local areas, there are serious damage to sheath blight, brown spot, rust, round spot, gray spot and so on; the main pests are corn borer, ground tiger, armyworm, red spider and so on.

Maize leaf spot and small leaf spot

[symptom identification] the typical symptom of corn leaf spot is that the small spot rapidly expands into a long prismatic spot, the serious one is more than 10 mi 30 cm long, and sometimes several spots are linked together to form irregular spots. The disease spot is immersed in water at first, and soon becomes green, and finally becomes black mildew, that is, the conidiophores and conidia of the pathogen.

[symptom characteristic] the symptom characteristic of corn leaf spot is that the disease spot is small, generally no more than 1 cm long, the width is only between two leaf veins, nearly oval, the color of the spot edge is dark, it is Auburn. In addition, the number of disease spots is generally more.

[pathogenic factors] the germination and invasion of spores and the formation and spread of spores all need certain climatic conditions, of which temperature and humidity are the main. The optimum temperature for spore formation, germination and invasion of Xanthomonas oryzae was 20 ℃ 25 ℃, while that of Xanthomonas oryzae was slightly higher than that of Xanthomonas oryzae, and the optimum temperature was 20 Mel 32 mol. Therefore, the small spot is more serious in the summer corn planting area, while the big spot is more serious in the spring corn area. Heavy rainfall and high humidity are easy to cause the epidemic of diseases.

[control methods] the prevalence of the disease is determined by three factors: first, planting susceptible varieties in a large area; second, the existence of a large number of bacteria; and third, suitable environmental conditions for the disease. Therefore, the prevention and control of diseases should start from these three aspects.

Selection of disease-resistant varieties for ①: this is the fundamental way to control large and small spot. There are obvious differences in disease resistance among different varieties. At present, the disease-resistant varieties commonly used in production are Baoyu 7, Tunyu 7, Yunrui 7, Haihe 14, Qing3, Huidan 4, Xinghuangdan 892, Denghai 3, Dianfeng 4, Yunrui 1, Yunrui 2, Yunrui 8, Ludan 10, Qichen 3, Haihe 2 and so on.

Deep ploughing of ② rotation can reduce the amount of bacteria, thoroughly remove the disease and residue in the field after corn harvest, and reduce the source of primary infection. In the early stage of the disease, the lower diseased leaves were knocked out before the disease occurred in the bottom 4 leaves, which could reduce the degree of the disease. It is suitable for early sowing and has the effect of avoiding disease. Strengthening the management of fertilizer and water can improve the disease resistance. The poor growth of the plant is easy to be infected, and the resistant varieties can not show their disease resistance potential even when they are short of water.

③ medicament control: 40% Ke Fei San emulsion 500ml 1000 times, 50% Tuichuite wettable powder 800x, 50% Daoxianjing 1000 times, 50% methyl topiramine 500,800 times. It is necessary to spray again every 7 days or so.

Maize head smut

It is mainly harmful to the ear and flowering of corn, and there is usually no harvest of the whole plant once the disease occurs. Therefore, the incidence of the disease is equal to the loss rate of the disease, and the harm is quite serious. Commonly known as "Wumi" or "gray bag".

[symptom identification] the symptoms of systemic diseases invaded from maize coleoptile at seedling stage were mainly after heading. The appearance of the diseased ear is shorter than that of the normal ear, the base is large and the tip is pointed, and there is no filament at the top. Sometimes one side of the bract split, revealing black powder, the diseased ear all turned into a dark brown pile of spores, the spores were not easily scattered, which were mixed with the remains of the vascular bundles of corn plants. The plants with smallpox disease generally have no spike, and the tip of the newly extracted flower axis becomes a small pile of black spores, and sometimes the floret deforms into leaves after smallpox extraction.

[pathogenic factors] chlamydospores fall into the soil, mixed with manure or carried by seeds to survive the winter. In the following year, under suitable conditions, chlamydospores germinated and invaded the host seedlings through the coleoptile. After the invasion, the hyphae entered the plant growth point, spread to the ear and smallpox, formed a pile of spores, and then released spores after maturation, completing the infection cycle once a year, and there was no further infection. When the soil temperature is low and dry, the emergence of maize seedlings is slow, which increases the chance of bacterial infection, and the incidence is high, which is conducive to the epidemic of head smut. Therefore, the occurrence of head smut is serious in cold areas. The pathogen can survive in the soil for about 3 years, and stubble for 3 years can effectively control the disease.

[prevention and control methods]

① selects disease-resistant varieties: at present, the disease-resistant varieties commonly used in production are Dianfeng 4, Ludan 10, Quchen 3, Baoyu 7, Haihe 14, Yunrui 1, Yunrui 2, Yunrui 7, Yunrui 8 and so on.

② implements rotation and deep ploughing: continuous cropping for many years is easy to increase the amount of bacteria in the soil and cause serious disease. The practice of rotation for more than 3 years can basically eliminate the harm of bacteria in the soil. Turning deep into the soil and pressing the spores below the sowing layer can reduce the source of bacteria and reduce the disease.

③ early extraction of diseased plants: when the white membrane of the diseased ear is not ruptured, pull out the diseased plant, and take the diseased plant out of the ground and bury it or burn it, so as to prevent the bacteria from falling into the soil.

④ chemical control: this disease is an one-time infection disease in the seedling stage, the use of chemicals to prevent the invasion of bacteria in the seedling stage will effectively control the occurrence of the disease. First, the control effect can reach about 90% when seeds are mixed with 25% trimethoprim or hydroxyrustine at a dose of 0.3%. Corn paste can also be used as an adhesive to increase efficacy. Second, the use of seed coating agents to prevent diseases. At present, there are many kinds of coating agents in production, which can effectively control diseases and insect pests.