Latest Corn Pest and Disease Prevention and Control Techniques: A Step-by-Step Guide
During the production process, corn is often harmed by various pests and diseases, causing severe yield reductions. For example, in years when northern corn leaf blight is epidemic, yields can be reduced 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, stalk rot, ear and kernel rot, and viral diseases. In some areas, sheath blight, brown spot, rust, round spot, and gray leaf spot cause severe damage; the main insect pests include the Asian corn borer, cutworm, armyworm, and red spider mite.
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 spots, with severe ones reaching 10—30 cm or more, and sometimes several lesions join together to form irregular large spots. The lesions are initially water-soaked, quickly turn grayish-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 no 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 and invasion of pathogen spores, as well as spore formation and dissemination, 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 southern corn leaf blight is slightly higher than that of northern corn leaf blight, with an optimum temperature of 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.
[Prevention and Control Methods] The epidemic of a disease is determined by three factors: first, large-scale planting of susceptible varieties; second, the presence of large amounts of pathogens; third, the presence of environmental conditions suitable for disease development. Therefore, disease prevention and control should start from these three aspects.
① Select disease-resistant varieties: This is the fundamental approach to preventing and controlling northern and southern corn leaf blight. Different varieties have obvious differences in disease resistance. Currently commonly used resistant varieties in production 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.
② Crop rotation, stubble turnover, and deep plowing can reduce the amount of inoculum. After corn harvest, thoroughly remove diseased residues from the field to reduce the primary infection source. In the early stage of disease onset, 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 show their disease resistance potential when lacking water.
③ Chemical 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 after about 7 days.
Corn Head Smut
It mainly harms corn ears and tassels, and once the disease occurs, the whole plant usually produces no grain at all. Therefore, the disease incidence rate equals the loss rate, and the damage is quite severe. Commonly known as “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. Diseased ears appear shorter than normal ears, with a large base and pointed tip, and no silks emerge from the top. Sometimes one side of the husk splits open, revealing black powder. The diseased ear entirely becomes a black-brown spore mass, the spores are not easily dispersed, and it is mixed with remnants of corn plant 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 spores, and sometimes after the tassel emerges, the florets are deformed into leaf-like structures.
[Disease Factors] The pathogen's chlamydospores fall into the soil, mix with manure, or are carried by seeds to overwinter. The following year, under suitable conditions, the chlamydospores germinate and invade host seedlings through the coleoptile. After invasion, the hyphae enter the plant growth point and, as the plant grows, spread to the ears and tassels, 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 relatively dry, corn emergence is delayed, increasing the chance of pathogen infection, resulting in high disease incidence and favoring the epidemic of head smut. Therefore, in cool regions, head smut occurs more severely. This pathogen can survive in soil for about 3 years, and a 3-year crop rotation can effectively control this disease.
[Prevention and Control Methods]
① Select disease-resistant varieties: Currently commonly used resistant varieties in production 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.
② Implement crop rotation and deep plowing: Continuous cropping for many years easily increases the amount of pathogens 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 of the soil presses pathogen spores below the sowing layer, which can reduce the inoculum source and lessen disease occurrence.
③ Pull out 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 deep bury or burn them, so as to prevent pathogens from falling into the soil.
④ Chemical 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 at a 0.3% dose for seed dressing, 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. Currently, there are many coating agents available in production that can effectively prevent and control pests and diseases.
Corn Ear and Kernel Rot
Corn ear and kernel rot is divided into many types due to different pathogens harming corn, mainly including Fusarium rot, Aspergillus ear rot, Penicillium ear rot, and dry rot caused by Diplodia species.
[Symptom Identification] The ear begins to develop disease from the top or base, with large areas or the entire ear rotting. Diseased kernels are shriveled, dull, and not plump, and sometimes pink or gray-white mycelium is produced between kernels. Some symptoms appear only on individual or local kernels, on which dense red powdery material grows, and diseased kernels are easily broken. Some pathogens (such as Aspergillus flavus and Fusarium) produce toxins during growth. Kernels with ear and kernel rot caused by these pathogens can cause dizziness, nausea, and vomiting when made into products or directly consumed by humans. When diseased kernels are used as feed, they often cause vomiting in pigs, and in severe cases can cause the death of livestock and poultry.
[Disease Factors] Infected seeds, diseased residues, and diseased residues of other crops can all cause field disease onset, and in years with heavy rain in the later period, they easily cause disease epidemics.
[Prevention and Control Methods]
First, select disease-resistant varieties. Currently relatively resistant varieties include Baoyu No. 7, Tunyu No. 7, Yunrui No. 7, Haihe No. 14, Qingsan, Huidan No. 4, Dianfeng No. 4, Yunrui No. 1, Yunrui No. 2, Yunrui No. 8, Ludan No. 10, Quchen No. 3, Haihe No. 2, etc.
Second, collect diseased residues, burn or deep bury them, and implement 2—3 year crop rotation.
Third, use coated seeds.
Fourth, strengthen field management to achieve robust plant growth and improve disease resistance. Timely control the Asian corn borer, because the Asian corn borer is the infection vector of ear and kernel rot pathogens.
Fifth, during storage, maintain ventilation, dryness, and low temperature.
Corn Stalk Rot
Corn stalk rot mainly occurs at the late grain-filling stage. It is an explosive, destructive disease that easily causes severe yield losses.
[Symptom Identification] At the late grain-filling stage of corn, it often shows sudden green wilting, with the whole plant's leaves drying up and fading like water-scalded; the ear droops and the husk dies; the stem base is initially water-soaked, then gradually turns light brown, and when squeezed by hand it feels hollow, often leading to lodging.
[Disease Factors] First, caused by Fusarium; second, caused by Pythium; third, caused by combined infection of Pythium and Fusarium. Heavy rain from the grain-filling to milk-ripe stage has an important impact on disease occurrence, and high soil water content is an important condition for the occurrence of stalk rot.
[Prevention and Control Methods] Select disease-resistant varieties Tunyu No. 7, Ludan No. 10, Yunrui No. 1, Yunrui No. 2, Baoyu No. 7, Yunrui No. 7, Haihe No. 14, Qingsan, Huidan No. 4, Dianfeng No. 4, Yunrui No. 8, Quchen No. 3, Haihe No. 2. In cultivation measures, attention should be paid to drainage.