Corn stem rot, also known as corn stalk rot or bacterial wilt, has become a serious issue in recent years. This disease is often caused by the widespread planting of inbred lines and hybrid varieties that lack resistance, especially after frequent exchanges between different regions. As a result, the disease spreads rapidly across corn-producing areas, leading to plant wilting, underdeveloped ears, and significant yield losses for farmers and companies alike. The incidence rate of intercropped maize and summer-sown corn can reach up to 10%–25%, with some cases even exceeding 48.6%, causing a production loss of about 25%. Currently, the main method of control relies on resistant varieties. However, due to the long breeding cycle, many varieties become susceptible within 4–5 years, creating instability in production. To address this, it's essential to understand the disease's occurrence patterns and implement comprehensive prevention strategies.
**First, Understanding the Disease Occurrence**
1. **Symptoms and Characteristics:**
Corn stem rot is a systemic disease that affects the entire plant. It typically becomes most noticeable during the milk and wax ripening stages. Symptoms vary depending on the pathogen involved:
- **Blue and Dry Type:** Infection starts from the lower leaves, spreading upward with water-soaked, blue-green lesions. In severe cases, the whole plant may suddenly wilt, especially after rainy days.
- **Stem Rot Type:** Affected plants have stunted roots and soft, rotted stems. The pith becomes loose, and the roots may show white or pink mold, depending on the stage of infection.
- **Ear Rot Type:** Infected ears droop, the husks become soft, and the kernels appear gray and dull.
2. **Cause of the Disease:**
Stem rot is primarily caused by pathogens like *Pythium* and *Fusarium*, which thrive in different environmental conditions. *Pythium* prefers cooler, wetter soils, while *Fusarium* thrives in warmer, drier conditions. The disease is soil-borne and persists in infected tissues and soil, re-infecting crops in subsequent seasons. Factors such as continuous cropping, poor drainage, and high humidity increase disease risk. Varieties with a more open growth habit are generally more resistant than compact ones. For example, summer corn varieties tend to be more resistant than spring corn, with specific hybrids like Zhongyu No. 5 and Nongda 3138 showing strong resistance.
**Second, Comprehensive Prevention and Control Measures**
1. **Breeding Resistant Varieties:**
Selecting and cultivating resistant inbred lines and hybrids is crucial. Recent efforts have led to the development of several resistant varieties, including Bai Ji 815, Va35, and Zhongdan 11, among others.
2. **Removing Diseased Residues:**
Prompt removal and burning of diseased plants after harvest helps reduce pathogen buildup in the field.
3. **Crop Rotation:**
Rotating maize with non-host crops like rice, potatoes, or vegetables can break the disease cycle and reduce pathogen accumulation in the soil.
4. **Appropriate Sowing Time:**
Delaying sowing, especially in northern regions, can help avoid peak disease periods. Late planting can reduce disease incidence by 11.3%–67.5% and improve yields.
5. **Rational Fertilization:**
Applying potassium, phosphorus, and nitrogen fertilizers at critical growth stages improves plant health and reduces susceptibility. For example, applying 100–150 kg/ha of potassium sulfate can significantly enhance yield.
6. **Biological Control Methods:**
Using beneficial microorganisms like *Trichoderma harzianum* or seed treatments with biocontrol agents can effectively suppress pathogen activity. These methods offer a sustainable alternative to chemical pesticides.
By combining these strategies, farmers can better manage corn stem rot, reduce economic losses, and ensure more stable and productive harvests.
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