Rice blast

　　Rice blast, also known as "burning blight," gets its name from the fact that it resembles a plague—quite frightening, though not quite as terrifying as Ebola. This disease is one of the "Three Friends" of rice diseases, much like the "Three Friends of Winter"—plum, orchid, and chrysanthemum. The severity of this disease varies depending on the rice variety, cultivation techniques, and climatic conditions—a statement often made by experts that’s more of a generalization than a precise observation. Let me just parrot what the experts usually say: In years when the disease is prevalent, rice yields typically drop by 10% to 15%, and in severe cases, the reduction can reach as high as 30% to 50%. Pretty scary, isn’t it? Early-maturing indica rice tends to be less affected (indica rice is the basic type of rice, generally grown in low-altitude, hot-and-humid regions), whereas late-maturing japonica rice is more prone to infection—especially glutinous and sticky rice varieties. Along riverbanks and coastal areas, the disease strikes particularly hard year after year, often causing significant damage. (Japonica rice is a variant of rice cultivated in higher-altitude regions; it’s not very tolerant of high temperatures. As for glutinous rice, that’s the kind we use to make sweet rice wine—two glasses, boss, please!)

　　(1) Rice Blast Identification and Occurrence

　　Rice blast can occur at any growth stage and in any part of the rice plant. Depending on the timing and location of infection, the disease can be classified into seedling blast, leaf blast, leaf sheath blast, node blast, panicle neck blast, rachis blast, and grain blast, among others. To make it easier for everyone to remember, Xiao Li has come up with a unique technique—“Seven Palm Techniques for Controlling the Disease.” Of course, compared to Master Jin Yong’s “Eighteen Dragon Subduing Palms,” ours are more like the grandsons’ version—so just laugh about it!

　　1. Seedling blast—this is the number-one disease to watch out for. The pathogen lies dormant in the seedlings, much like a hidden dragon lurking deep in the abyss. This disease is often caused by seed-borne pathogens and can severely damage seedlings in both single-season and late-season rice fields. Typically, this disease makes its appearance before the rice plants reach the three-leaf stage. Once it strikes, water-soaked spots begin to appear on the shoots and sheaths; these lesions are not very obvious at first. However, the portion of the diseased seedlings close to the soil surface turns grayish-black, covered with a grayish mold. The upper parts of the seedlings tend to yellow, curl up, and eventually die. If you were to get hit by this disease, it’d probably leave you looking just as grayish-black—and your hair would be scorched into a yellowish-brown, frizzy mess.

　　The “Two-Leaf Blast” technique packs a tremendous punch. Right now, as the disease is raging in the fields, the dragon is already wreaking havoc across the paddies. Once this technique is unleashed, it can strike both seedlings and mature plants, leaving behind lesions that initially appear as tiny brown spots—no bigger than the head of a pin—and quickly expand into short spindle-shaped or diamond-like lesions, densely covered with irregular small spots that are either gray-green or brown. In humid conditions, the affected areas develop a gray-green mold layer. In severe cases, entire patches of seedlings can wither and die outright. Pretty nasty, isn’t it? Little Li isn’t pulling your leg—once this technique hits you, you’ll start noticing tiny brown spots all over your body, which will then rapidly grow into spindle-shaped, diamond-like lesions. Even if you don’t turn gray-green, you’ll definitely end up turning brown. If you’re hit hard by this technique, just brace yourself for wilting and eventual death. Typically, this disease peaks during the tillering stage; when it strikes severely, from afar, the infected fields look as though they’ve been scorched by fire. Of course, this disease exhibits four distinct symptom patterns—meaning this single technique has four different manifestations!

　　Type 1, the acute form: The lesions are irregular in shape, ranging in size from pinhead to nearly the size of a mung bean. The lesion edges are slightly pointed, water-soaked, dark green, and densely covered with gray-green mold. The appearance of acute lesions is a clear sign that rice blast is about to break out. The rivers and lakes are dangerous—run fast!

　　Type 2—chronic and acute lesions—can transform into chronic lesions under dry weather conditions, when plant resistance increases, or following chemical control measures. The lesions are spindle-shaped; the yellowish outer ring indicates the area affected by toxicity, while the brownish interior represents the necrotic tissue. The grayish-white center signifies the collapsed tissue. The brownish necrotic lines extend outward from the lesion and radiate toward both ends—a key characteristic of rice blast. In humid weather, a gray-green mold often appears along the edges or on the reverse side of the lesion.

　　Type 3, brown spot type: The lesions appear as small brown spots confined between leaf veins. In dry weather, they typically occur on the lower and middle leaves of rice plants with strong disease resistance. Under moderate temperatures and high humidity, some lesions may develop into chronic forms.

　　Type 4: White Spot Type—This type of lesion is rare and typically appears under unfavorable climatic conditions during the symptomatic stage. It’s highly unstable; however, when weather conditions become favorable for disease development, it can transform into an acute-type lesion. Remember to combine quick and slow approaches in this technique—this will greatly enhance your attack efficiency. You don’t need to practice the other two techniques.

　　3. Sheath Blight (also known as Neck Blight)—this technique is called “The Soaring Dragon Regrets.” Why is it called that? Because this disease primarily affects the sheath and rachis of the spike or the small pedicels, causing the most significant impact on yield. If you contract this disease, will you regret it? Don’t regret it—just turn to Xiao Li. I’ll take full responsibility for you. In the early stages, the disease manifests as small, light-brown lesions with a water-soaked, chlorotic border. Later, the affected area expands both upward and downward, eventually reaching 2 to 3 centimeters in length. The color deepens, and the lesion ultimately turns black, leading to withering and death or breakage of the spike, resulting in shriveled grains or even white spikes. Do you regret it or not?

　　4. Neck Blight, also known as "Flying Disease on the Node vs. Flying Dragon in the Sky," typically occurs on the first and second nodes below the ear. At the node, small dark-brown spots appear and gradually expand in a ring-like pattern, eventually turning the entire node black. This leads to bending or breakage of the stem at the node. Pretty severe, isn't it? The Flying Disease can prematurely end your life—killing you in the cradle, quite literally.

　　5. Grain blight—the “dragon’s head nod” corresponds to the “dragon’s tail swish.” In the grain area—specifically, the head—early-onset lesions appear elliptical, with a grayish-white center; later, the entire grain turns into a dull-gray, shriveled grain. In cases of late onset, irregular dark-brown spots often develop.

　　Let’s stop here for now. The key to mastering this technique still lies with the pathogen. The pathogen overwinters on seeds and straw, using mycelia and conidiospores—its asexual reproductive structures—to survive. Once seeds carrying the pathogen are sown, they can immediately trigger seedling blast. As the weather warms up and rainfall increases, creating humid conditions, large numbers of pathogens are released from infected plants, spreading through the air via wind and infecting young rice seedlings or mature rice plants in the field. Subsequently, the pathogen continues to multiply relentlessly on diseased plants, repeatedly reinfecting and causing further damage. Pathogen spores, carried by the wind, land on rice plants and, as soon as they encounter even a single drop of water, germinate, penetrate the plant tissues, absorb nutrients, and destroy cells. At its fastest, you can observe visible disease lesions at the site of infection within just four days. It seems that even viruses understand the principle of repaying kindness with gratitude—giving back tenfold what one has received. Everyone, please take this as your guiding principle in life!

　　(2) Pathogenic conditions,

　　The outbreak of rice blast is the result of a combination of factors, much like an epidemic—no one can predict with certainty when and how severely it will strike. The primary factor determining the varying severity of the disease from year to year is climatic conditions. Meanwhile, the main factors influencing differences in disease severity among individual fields are cultivation management practices and the disease resistance of the rice varieties grown. Generally speaking, proper fertilizer and water management can enhance rice plants' disease resistance, thereby mitigating the impact of the disease even in years when outbreaks are severe.

　　1. Climate: The temperature range of 24 to 28 degrees Celsius is most conducive to the formation and invasion of pathogen spores. Relative humidity above 92%—when both these conditions are present simultaneously, disease development is favored. If either one of these conditions is missing, the disease either won't occur at all or will develop very slowly. All of the above may sound like common sense, but in reality, it doesn't always apply in practice. During the tillering and heading stages, if the rice plants encounter low temperatures and rainy weather, they tend to grow weakly and become less resistant to disease, often leading to the outbreak of neck blast. This is just like how, during pregnancy, a person's immune system weakens, making them more susceptible to catching colds and other illnesses—kind of like being "picked up" by Uncle Cold for some fun!

　　2. Improper fertilization—especially excessive application of nitrogen fertilizer, particularly when applied too late—often triggers severe outbreaks of blast disease in the panicle neck. I’m telling you, fellow farmers: What’s the point of applying so much nitrogen? Are you just throwing money away because you’ve got more than you know what to do with? Why not give it to Xiao Li? Xiao Li could tell you some interesting stories and keep you entertained, wouldn’t that be a lot more fun?

　　3. The disease resistance of different rice varieties varies depending on the variety itself. Even within the same variety, resistance to blast disease differs across various growth stages. Generally, the plant is most susceptible to blast during the four-leaf stage, tillering stage, late booting stage, and at the onset of heading. Of course, humans—from infancy to old age—also experience varying degrees of susceptibility to diseases at different life stages.

　　Third, don't walk away—exciting content is coming right up! The most useful, practical, and cutting-edge stage is here: prevention and control measures.

　　Adopting a comprehensive control strategy—based on cultivating high-yield, disease-resistant varieties, focusing on strengthening fertilizer and water management, and promptly applying pesticides once the disease appears—this is what experts recommend. But these days, do Chinese people really trust experts?

　　1. Select high-yielding, disease-resistant varieties: Choose high-yielding, disease-resistant varieties that are well-suited to local conditions. At the same time, pay attention to the rational arrangement of different varieties to prevent monoculture and ensure regular rotation and renewal of varieties. Now, did hearing this first point make you feel like vomiting?

　　2. Promptly dispose of diseased rice straw and handle it properly, as well as weeds from infected areas. Do not pile up diseased rice straw near seedling beds, and never use diseased straw as a germination cover or for tying seedlings—this could spread pathogens into the paddy fields. You can keep spitting—it’s okay; Xiao Li won’t pull you down.

　　3. You’ve already vomited, right? After vomiting, proceed with seed disinfection: Prepare a solution by diluting 80% allicin emulsifiable concentrate at a ratio of 1:2,000. Soak 30–50 kg of seeds in every 50 kg of the solution for 2 days. After thoroughly rinsing off the solution, proceed with germination promotion. You might want to give this method a try—it’s reportedly quite effective.

　　4. Strengthen fertilizer and water management: Use a balanced combination of nitrogen, phosphorus, and potassium; increase the application of organic fertilizers; adhere to the principle of applying sufficient base fertilizer and early topdressing; prevent excessive use of nitrogen fertilizer in the later stages; and pay attention to appropriately increasing the application of phosphorus and potassium fertilizers. During the early growth stage of rice, maintain shallow-water irrigation frequently. At the end of tillering, promptly drain the fields—allowing them to dry out—and in the later stages, ensure adequate "running-water" irrigation, keeping the fields moist until maturity. This promotes robust stems, vigorous roots, and enhanced disease resistance, thereby reducing the incidence of diseases.

　　5. Absolutely don't walk away—here comes some practical science-based knowledge! For chemical control of diseases, to effectively manage seedling blight and leaf blight, it's crucial to apply pesticides at the very early stage of disease onset and promptly eliminate the disease’s focal points. To control neck blast, apply a single treatment during the late booting stage through the heading stage; then, depending on weather conditions, apply a second treatment at the uniform heading stage. As for the choice of pesticide, you can use either 100 grams of 20% triadimenol wettable powder per 666 square meters, or 80–100 milliliters of 25% imazalil aqueous solution, or 75–115 milliliters of 40% kasugamycin emulsifiable concentrate, diluted in 40–45 kilograms of water, and spray evenly.