Corn Pest and Disease Control Techniques and Methods Explained in Detail

During production, corn is often harmed by various diseases and pests, causing severe yield reductions. For example, in epidemic years of northern corn leaf blight, yields can drop by 15—30% due to the disease, and severely affected fields can lose more than 50%; damage from the Asian corn borer typically reduces corn yields by about 10%, and in severe years by about 30%. There are many types of pests and diseases that harm corn. The main diseases include northern corn leaf blight, southern corn leaf blight, head smut, bacterial stalk rot, ear and kernel rot, and viral diseases. In certain localized areas, sheath blight, brown spot, rust, round spot, and gray leaf spot cause severe damage; the main pests include the Asian corn borer, cutworms, armyworms, and spider mites.

Northern and Southern Corn Leaf Blight

[Symptom Identification] The typical symptom of northern corn leaf blight is that small lesions rapidly expand into long spindle-shaped large lesions, with severe ones reaching more than 10—30 cm in length; sometimes several lesions join together to form irregular large lesions. The lesions are initially water-soaked, quickly turn bluish-green, and finally become black moldy masses, which are the pathogen's conidiophores and conidia.

[Symptom Characteristics] The symptom characteristic of southern corn leaf blight is that the lesions are small, generally not more than 1 cm long, with width limited between two leaf veins, nearly elliptical, and the lesion margins are darker in color, reddish-brown. In addition, the number of lesions is generally relatively large.

[Disease Factors] The germination, invasion, formation, and spread of pathogen spores all require certain climatic conditions, among which temperature and humidity are the main ones. The optimum temperature for spore formation, germination, and invasion of the northern corn leaf blight pathogen is 20—25°C, while that of the southern corn leaf blight pathogen is slightly higher, at 20—32°C. Therefore, southern corn leaf blight is more severe in summer corn planting areas, while northern corn leaf blight is more severe in spring corn areas. High rainfall and high humidity easily cause disease epidemics.

[Control Methods] A disease epidemic is determined by three factors: first, large-scale planting of susceptible varieties; second, the presence of a large amount of pathogen; third, the presence of environmental conditions suitable for disease development. Therefore, disease control should start from these three aspects.

①Select resistant varieties: This is the fundamental approach to controlling northern and southern corn leaf blight. Different varieties have obvious differences in resistance to the disease. Resistant varieties commonly used in production at present include Baoyu No. 7, Tunyu No. 7, Yunrui No. 7, Haihe No. 14, Qingsan, Huidan No. 4, Xinghuangdan 892, Denghai No. 3, Dianfeng No. 4, Yunrui No. 1, Yunrui No. 2, Yunrui No. 8, Ludan No. 10, Quchen No. 3, Haihe No. 2, etc.

②Rotation, stubble turnover, and deep plowing can reduce the amount of pathogen. After corn harvest, thoroughly remove diseased plant residues from the field to reduce the primary infection source. In the early stage of disease, removing the lower diseased leaves before the bottom 4 leaves become diseased can reduce the severity of the disease. Early sowing at the appropriate time has a disease-avoiding effect. Strengthening fertilizer and water management can improve disease resistance. Poor plant growth makes plants susceptible to infection; even resistant varieties cannot express their disease resistance potential when lacking water.

③Chemical control: Use 40% Kitazin emulsifiable concentrate at 500—1000 times dilution, 50% Tuzet wettable powder at 800 times dilution, 50% Inezin at 1000 times dilution, or 50% thiophanate-methyl at 500—800 times dilution. If necessary, spray again about 7 days later.

Corn Head Smut

It mainly harms corn ears and tassels, and once the disease occurs, usually the whole plant produces no grain at all. Therefore, the incidence rate of this disease equals the loss rate from the disease, and the damage is quite severe. It is commonly called "wumi" or "huibao."

[Symptom Identification] It is a systemic disease that invades from the corn coleoptile at the seedling stage, with symptoms mainly appearing after tasseling. The diseased ear looks shorter than a normal ear, with a broad base and pointed tip, and no silks emerge from the top. Sometimes the husk on one side splits open, exposing black powder. The diseased ear entirely becomes a black-brown spore mass, and the spores do not disperse easily, mixed with remnants of the corn plant's vascular bundles. Plants with diseased tassels generally have no tassel branches; the tip of the newly emerged tassel axis becomes a small pile of black spore mass, and sometimes after the tassel emerges, the florets become deformed into leaf-like structures.

[Disease Factors] The pathogen's chlamydospores fall into the soil, mix into manure, or are carried by seeds to overwinter. The following year, under suitable conditions, the chlamydospores germinate and invade the host seedling through the coleoptile. After invasion, the hyphae enter the plant growth point and, as the plant grows, spread to the ear and tassel, forming spore masses, and after maturity release spores again, completing its once-a-year infection cycle, with no secondary infection occurring. When soil temperature is relatively low and conditions are relatively dry, corn emergence is delayed, increasing the chance of pathogen infection, and the incidence rate is high, which favors the epidemic of head smut. Therefore, in cool regions, head smut occurs more severely. This pathogen can survive in the soil for about 3 years, and rotating crops for 3 years can effectively control this disease.

[Control Methods]

①Select resistant varieties: Resistant varieties commonly used in production at present include Dianfeng No. 4, Ludan No. 10, Quchen No. 3, Baoyu No. 7, Haihe No. 14, Yunrui No. 1, Yunrui No. 2, Yunrui No. 7, Yunrui No. 8, etc.

②Implement crop rotation and deep plowing: Continuous cropping for many years easily increases the amount of pathogen in the soil, resulting in severe disease. Implementing crop rotation for more than 3 years can basically eliminate the harm of pathogens in the soil. Deep plowing the soil to press pathogen spores below the sowing layer can reduce the pathogen source and lessen disease occurrence.

③Remove diseased plants early: Pull out diseased plants before the white membrane of the diseased ear ruptures, and take the diseased plants outside the field to bury deeply or burn, so as to prevent the pathogen from falling into the soil.

④Chemical control: This disease is a one-time infection disease at the seedling stage. Using chemicals at the seedling stage to prevent pathogen invasion will effectively control the occurrence of this disease. First, use 25% triadimefon or triadimenol, seed-dressed at a dose of 0.3%, and the control effect can reach about 90%. Corn paste can also be used as an adhesive to increase efficacy. Second, use seed coating agents to prevent disease. At present, there are many coating agents in production that can effectively control pests and diseases.