How to prevent and control common corn pests and diseases? A detailed explanation of prevention and control measures
Pest and Disease Control Strategies for Organic Corn Cultivation The diseases that easily occur during corn cultivation are leaf spot, smut, rust, and mosaic virus, while the pests include corn borers and aphids. The occurrence of pests and diseases is closely related to climatic conditions, so the timing of control should be decided according to climatic factors and field diseases
Pest and Disease Control Strategies for Organic Corn Cultivation
The diseases that easily occur during corn cultivation are leaf spot, smut, rust, and mosaic virus, while the pests include corn borers and aphids. The occurrence of pests and diseases is closely related to climatic conditions, so the timing of control should be decided according to climatic factors and the occurrence of pests and diseases in the field. The symptoms and damage patterns of the main corn pests and diseases are described below, and control work is carried out using clove oil, neem extract, release of egg parasitoid wasps, and microbial preparations.
1. Corn leaf spot (southern corn leaf blight):
⟦NL> It mainly harms the leaves. At first there are pinhead-sized spots, which later become light brown lesions. Restricted by the leaf veins, they become elongated or spindle-shaped, light brown in the center with dark brown edges. It can occur throughout all growth stages of corn during the year, and is most likely to occur when the temperature is 20-32°C, with more leaf spot disease on the middle and lower leaves. When it occurs, spray a 400-fold clove oil solution for control, and the estimated control rate can reach 70-75%.
2. Corn smut:
It mainly harms the leaves. At first there are pinhead-sized spots, which gradually expand into water-soaked spindle-shaped gray-green lesions 2-15 cm long, and under high humidity a gray-black moldy substance appears on the surface. In the mid-growth period of the spring crop, that is, from late March to mid-May, when the temperature is 18-27°C and humidity is high, it is most likely to occur. In winter and summer, the temperature is unsuitable, so it rarely occurs. The control method is the same as for leaf spot. The estimated control rate can reach 70-75%.
3. Corn rust:
It is divided into common rust and southern rust. The lesions are mostly seen on the leaves, but the leaf sheaths and husks can also be infected. The uredinia of common rust form under the leaf epidermis and, after rupturing, produce coffee-colored powdery urediniospores. The uredinia of southern rust are embedded under the leaf epidermis, small and round, and golden yellow. Seedlings are more susceptible to infection, but in the field it mostly occurs in the middle and late growth stages. The control method is the same as for leaf spot. The estimated control rate can reach 70%.
4. Corn mosaic virus disease:
Maize dwarf mosaic virus strain B is the main pathogen, and it infects healthy plants through mechanical transmission or aphid vectors. In the early stage of the disease, dense yellow spots appear at the base of the leaves and then spread across the whole leaf, forming a mosaic symptom of alternating yellow and green. In severe cases, the leaves become chlorotic and yellow, and even the stems, leaf sheaths, husk leaves, and male flowers all show mosaic patterns. If infected at the seedling stage, there is slow growth and plant dwarfing. For the control method: if corn is infected at the 6th or 7th leaf stage, one additional application of nitrogen fertilizer can be made to promote the growth of diseased plants; if infection occurs after the 8th leaf, the impact on yield is very small and can be ignored, so no control is needed. In addition, attention should be paid to the control of the vector insect, the corn aphid.
5. Corn borer:
It is the most important pest of corn, and corn sown between March and September suffers more serious damage. Adults are active late at night and lay egg masses on the underside of corn leaves on plants about 20 cm or more in height. The hatched larvae damage all parts of the corn and finally pupate in the damaged parts. For the control method, starting when the plant height is 20 cm, release Trichogramma egg parasitoid wasps, applying 200 egg cards per hectare to suppress the hatching of corn borer eggs. In addition, apply Bacillus thuringiensis (16000 iu/mg) granules into the leaf whorl at the early whorl stage, mid-whorl stage, 4-5 days before tassel emergence, and 3-4 days after silking. The dosage is 5 kg per hectare. The preventive control rate can reach 70-80%.
6. Corn aphid:
It is a major pest in the late growth period of corn, especially when the climate is dry, the damage is severe. Aphids gather on the leaf whorl or husk leaves, male flowers, and female flower stalks to suck sap and cause damage, resulting in poor plant growth. When it occurs, spray a 4.5% neem oil 2500-fold solution for control. The estimated control rate can reach 70-80%.