Symptoms and control techniques of corn bacterial wilt

Corn bacterial wilt is a major disease that affects corn during its mid to late growth stages. It is a systemic, invasive disease that can infect the entire plant. The peak period of infection usually occurs from the end of the grain-filling stage to the wax-ripe stage. The disease typically starts from the lower leaves and gradually moves upward, causing symptoms such as green blight. As it progresses, the entire plant becomes visibly affected, making it easy to distinguish from healthy plants. Some strains of the bacteria cause acute symptoms, where the whole plant suddenly wilts and dies during the milk or wax stage, without a gradual progression from the bottom up. This type of sudden death is more common after heavy rainfall. The time from the initial infection to the complete wilting of the plant can vary, ranging from one to three days in severe cases, or lasting more than 15 days in milder situations. Affected plants often show softening at the base of the stem, which becomes loose and easily bent when exposed to wind. Some ears may droop, and the stalks become weak and difficult to peel. The leaves remain green but dry out, while the roots are stunted, short, and often blackened and rotting. The internal pith of the stem becomes loose, and the kernels of the infected ear are loosely attached, making them easy to thresh and appearing dull and gray in color. **Disease Characteristics:** The bacteria overwinter in the soil and enter the plant through the roots during the early stages of corn growth, particularly up to the silking stage. High temperatures and humidity during the grain-filling to maturity phase promote rapid disease spread, with peak occurrences commonly observed on sunny days following rain. There is a significant variation in resistance among different corn varieties, with dwarf, early-maturing, and double-eared types being more susceptible. Overly dense planting, excessive nitrogen fertilizer application, and the use of unfermented crop residues as fertilizer can all contribute to higher disease incidence. Fields with low ground and waterlogging are also more prone to infection. Additionally, damage caused by hail, insect pests, or other physical injuries can create entry points for the pathogen, facilitating disease development. **Control Measures:** 1. **Plant Resistant Varieties:** Cultivating disease-resistant and high-yielding corn varieties is an effective long-term strategy to reduce the risk of bacterial wilt. 2. **Remove Infected Plants:** After harvest, all diseased plant residues should be removed, burned, and incorporated into the soil to prevent the spread of pathogens. 3. **Crop Rotation:** In fields with a history of heavy infection, rotating with non-corn crops for 2 to 3 years can help break the disease cycle. 4. **Proper Sowing Time:** Planting spring corn at the appropriate time can help avoid conditions that favor bacterial wilt development. 5. **Field Management:** Implementing proper agricultural practices such as fertilization, timely weeding, and drainage improvement can enhance plant health and resistance. Applying potassium or compound fertilizers during the jointing or booting stage can significantly improve disease prevention. 6. **Pest Control:** Controlling pests like corn borers and armyworms can reduce the likelihood of secondary infections and disease spread. *By Zhang Jinliang and Wang De (Farmers Daily)*

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