Symptoms and control techniques of corn bacterial wilt

Corn bacterial wilt is one of the most significant diseases affecting maize during its middle to late growth stages. It is a systemic, invasive disease that can affect the entire plant. The peak period for this disease usually occurs from the end of the grain-filling stage to the wax ripening stage. Typically, symptoms begin at the milk stage and gradually spread upward from the lower leaves, causing a condition known as "green blight." Eventually, the whole plant becomes visibly affected, making it easy to distinguish from healthy plants. Some strains of the bacteria cause acute symptoms, where the entire plant suddenly wilts and dies in the later milk or waxy stage without showing a gradual progression from the bottom up. This type of rapid onset is particularly common after heavy rainfall. From the initial infection to the point where the entire plant is affected, the disease usually takes about a week, though in some cases, it may develop in as little as 1 to 3 days, while in others, it can last more than 15 days. Affected plants show softening of the stem base, which becomes loose and easily bent when exposed to wind. Some ears sag, and the stalks become weak and difficult to peel. The leaves remain green but dry out, and the roots are stunted, short, and often blackened and rotten. The internal pith of the stem becomes loose, and the kernels of infected ears are loosely attached, making them easy to thresh and appearing dull and gray in color. **Disease Characteristics:** The bacteria overwinter in the soil and infect the corn plants through the roots during the early growth stages, such as after sowing and during the silking phase. High temperatures and humidity during the grain-filling to maturity stages create ideal conditions for disease development, with peak occurrences often observed on sunny days following rain. There are significant differences in resistance among corn varieties, with dwarf, early-maturing, and double-eared types being more susceptible. Overly dense planting, excessive nitrogen fertilizer use, and the application of unfermented crop straw as fertilizer can also contribute to disease severity. Fields with low-lying areas and standing water are especially vulnerable. Additionally, damage caused by hail, insect pests, or mechanical injuries can increase the likelihood of infection. **Control Measures:** 1. **Planting Resistant Varieties:** Choose and cultivate corn varieties that are resistant to bacterial wilt. 2. **Remove Infected Plants:** After harvest, completely remove and burn any diseased plant residues, and incorporate them into the soil through deep plowing. 3. **Crop Rotation:** In fields with a history of severe infection, rotate crops for 2 to 3 years with non-host plants to reduce pathogen buildup. 4. **Proper Sowing Time:** Plant spring corn at the appropriate time to avoid periods of high disease risk. 5. **Field Management:** Implement practices such as proper fertilization, timely weeding, and drainage improvement to promote plant growth and enhance resistance. Applying potassium or compound fertilizers during the jointing or booting stage can significantly improve disease control. 6. **Pest Control:** Timely management of pests like corn borers and armyworms can help reduce the occurrence of bacterial wilt. *By Zhang Jinliang and Wang De (Farmers Daily)*

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