Rice sheath blight

　　The disease known as "wén kū bìng," commonly referred to as "huā zú gǎn," gets its nickname because, once infected, the stems and lower parts of the rice plants turn visibly discolored—hence the term "flowered legs." This disease is caused by a fungus, so we might as well call it "rice foot fungus." Interestingly, just like human athlete's foot or tinea pedis, this fungal infection shares a similar mechanism of action. As one of the three major diseases affecting rice, this ailment has become increasingly severe in recent years, partly due to changes in rice cultivation practices, improvements in farming techniques, and increased fertilizer application rates. Typically, early-rice crops are more severely affected than single-season late-rice and second-season rice. In mild cases, the disease can impair grain filling—the process during which the developing rice grains absorb large amounts of nutrients. In severe cases, the disease causes the entire plant to wither and lodge, preventing it from heading altogether or leading to poor grain set even when it does head. In seriously affected fields, yield reductions can exceed 50%. Remember: it’s not just 10% or 20%; it’s a whopping 50%!

　　Let’s first talk about how to recognize this condition and its underlying causes:

　　Blast disease is a fungal infection that thrives in hot, humid conditions—just like how people with athlete’s foot tend to experience more severe symptoms during the hot, humid summer months. Typically, this disease first appears at the end of the tillering stage. (Tillering is the stage when, after you plant a seed, it starts branching out and branching out again—kind of like Nezha’s three heads and six arms, though this “arm” count is even higher.) The disease reaches its peak during the jointing and booting stages. (The jointing stage is when sunlight and fertilizers and water cause the rice plants to grow rapidly upward—a period akin to human puberty. During this time, people tend to be more active and lively, but also more prone to injury.) In the early stages of blast disease, small, elliptical, dark-green, water-soaked lesions first appear on the leaf sheaths near the water (the part that wraps around the leaves and stems—let’s call it the “little sheath”). As the disease progresses, these lesions gradually expand into cloud-like patterns—kind of reminiscent of those white cloud-like marks that form when a child wets the bed. Ha ha! However, the center of these lesions is grayish-white and turns grayish-green when the environment is damp. The lesions spread upward from the bottom, gradually increasing in number—much like how a condition might spread from the feet up the legs. The lesions on the leaves are similar to those on the leaf sheaths. When the panicle neck is affected, it becomes moist and turns bluish-black. In severe cases, the entire panicle can wither and die—just as if a person’s athlete’s foot were to spread all the way up to their neck, it would likely turn bluish-black too, and in extreme cases, could even prove fatal. Under conditions of high temperature and humidity, fungal hyphae gather on the surface of the infected tissues, initially appearing white before turning dark brown. Once mature, these hyphae become easily detached and fall onto the soil. (What exactly are hyphae? Hyphae are simply a structural component of fungi—think of them as individual members of a family, typically composed of a mom, a dad, and children. Each hypha is an individual entity.)

　　The pathogen primarily overwinters in the soil as sclerotia—these are clusters of mycelium that, once they reach a certain stage of growth, come together and form compact masses to stay warm during the cold winter months. The pathogen can also survive the winter as mycelial strands and sclerotia on diseased straw and other host plant residues. The following year, these nasty little sclerotia—oops, I mean, the nasty sclerotia—float to the water surface with irrigation water, then settle onto rice plants. When environmental conditions become favorable, the sclerotia give rise to mycelium, which invades the leaf sheaths and triggers disease development. From the infected areas, the mycelium spreads upward along the rice plants or toward neighboring rice plants.

　　Next, let’s talk about the conditions that trigger this disease—just like athlete’s foot, its transmission is also conditional.

　　1. Overcrowding, excessive or overly late application of nitrogen fertilizer can cause rice plants to grow rapidly and develop lush, tender green shoots. Additionally, excessively deep irrigation, poor drainage, inadequate aeration and light penetration, and high field humidity—all these factors promote the elongation and spread of fungal mycelium, thereby facilitating disease development. Simply put: imagine you already have athlete’s foot during the height of summer, and then you put on a pair of shoes that are too small, stuffy, and damp—just try walking around for a few steps and see what happens!

　　2. The disease is most prevalent in hot and humid environments. When the microclimate in the field ranges from 25 to 32 degrees Celsius and is accompanied by consecutive rainy days, the disease progresses particularly rapidly. Did you know that the old saying “a leaky roof meets continuous rain” actually originated from this very phenomenon? Remember: as soon as high temperatures are combined with prolonged rainy weather, misfortune is bound to strike!

　　3. Dwarf, high-yielding varieties, with their numerous tillers and densely packed leaves, are prone to disease. If you’re short, that’s fine—but if you’re also overweight, well, then what are you? You’re just a stone roller!

　　3. Prevention and control measures.

　　The book states that, based on agricultural control measures, special attention should be paid to fertilizer and water management, and chemical agents should be used to protect fields showing a serious tendency toward disease outbreaks.

　　1. Agricultural Control

　　1. Reduce the source of pathogens: Deeply plow rice fields to bury pathogen sclerotia deep in the soil, ensuring they’ll never resurface—this is entirely feasible. After preparing and flooding the rice fields, skim off the floating debris to minimize the sources of disease—this is what experts recommend. Fellow farmers, don’t listen to those eggheads; just ignore them! Combined with fertilization, remove weeds along field edges to eliminate wild hosts that harbor pathogens. When farming, always stay grounded and keep it real!

　　2. Strengthen cultivation management, focusing on reasonable plant density, and implement appropriate fertilizer and water management practices. Apply sufficient base fertilizer, carry out timely topdressing according to seedling conditions, and increase the application of phosphorus and potassium fertilizers. During the early growth stage, irrigate frequently with shallow water; in the mid-stage, temporarily suspend irrigation and allow the fields to dry slightly; in the later stage, alternate between wet and dry conditions. This approach ensures steady rice growth without excessive vigor, prevents premature greenness in the later stages, avoids lodging, and enhances disease resistance.

　　Clang, clang! Xiao Li has been talking all sorts of nonsense—but the most important and practical moment is about to arrive. Everyone, don’t just stare with wide-open eyes; what’s coming next is absolutely thrilling! If you miss it, you’ll regret it for the rest of your life. For chemical control, generally apply the first treatment at the very early stage of disease onset, and then repeat the spray every 10 days or so for one complete treatment course. The specific timing should be adjusted according to the current weather conditions and the trend of disease development. As for the choice of fungicide, you can use either: 70 grams of 15% Jinggangmycin soluble powder per 666 square meters, or 80 grams of 6% Jinggang-Snail Seed oil wettable powder, or 100 grams of 20% Jinggang-Layajun suspension concentrate. Depending on the rice’s growth stage, mix each formulation with 40–50 kilograms of water for foliar spray. For fields with severe disease outbreaks, choose 240 milliliters of thifluzamide per 666 square meters.

　　20 ml of suspension agent for spray treatment. I originally had a picture uploaded, but unfortunately, I can’t get it to upload—so never mind; just make do with what we’ve got. Looks like there’s something wrong with this website. If you find it inconvenient to view it here, feel free to check out our WeChat official account instead—starting tomorrow, we’ll be sharing tech insights daily.