Key Disease Control—Pepper Edition

　　Dead plants are the "primary culprit."

　　For vegetable farmers who grow hot (or sweet) peppers, the issue of pepper plants dying is a major headache—especially in greenhouses where the same crop has been grown for more than three consecutive years. Many farmers have experienced reduced yields or even complete crop failure due to plant death. After years of cultivation, farmers have concluded that the early stage of transplanting is a critical period for preventing plant death. Controlling plant death at this crucial stage is far more effective than applying root-soaking treatments during the peak fruiting period; it’s more than 50% cheaper and results in significantly less loss.

　　Through interviews, the author learned that there are multiple causes of pepper plant death. Besides root burn caused by excessive fertilization and root rot due to overwatering, diseases such as seedling blight, stem base rot, and root rot are also major contributors to plant death. These diseases are collectively referred to as soil-borne diseases. In production, sometimes a single disease occurs, while at other times multiple diseases occur simultaneously; among them, root rot is the primary cause of plant death. There are various types of pepper root rot. Right now, peppers grown in greenhouses are in their peak fruiting stage, yet many vegetable farmers have reported a serious increase in pepper plant deaths recently—some greenhouses even show that two-thirds of the plants have died, and the situation tends to worsen with increased watering. After observing several pepper greenhouses and talking with farmers, the reporter believes that the main diseases causing plant death are Fusarium root rot and Phytophthora root rot.

　　Fusarium root rot caused by Fusarium oxysporum primarily affects the roots of chili peppers. After uprooting the plants, one can observe that the root cortex has turned from light brown to dark brown and become rotten, resembling a mushy, bran-like substance that peels off very easily, exposing the underlying woody tissue, which darkens in color. The disease is mainly spread via water flow. Once infected, chili peppers exhibit wilting during the day, but recover from dusk until the following morning. This cycle repeats several times before the plants eventually die.

　　Medication regimen: Use a 1,000-fold dilution of 50% chlorobromoisocyanuric acid soluble powder mixed with an 800-fold dilution of 3% metalaxyl-mandipropamid for root irrigation. At the same time, when watering, isolate the affected plants to prevent the pathogen from spreading to other plants.

　　Phytophthora root rot in peppers is primarily spread via water runoff. However, the pathogen can also infect the base of the pepper plant’s stem, causing water-soaked rot and constriction at the base of the plant. The affected areas turn dark brown or black. After pulling up the infected plants, you’ll notice that their roots are also water-soaked and rotten. This disease mainly affects mature pepper plants. For plants that have already died from the disease, dig them out, carefully wrap them in plastic bags, and remove them from the greenhouse to prevent widespread infection.

　　Treatment regimen: The causal agent of Phytophthora root rot is primarily an oomycete. Vegetable farmers can use a mixture of 58% Ridomil at a dilution of 500 times, combined with 72.2% Pulik at a dilution of 600 times, or alternatively, use 50% Dimethomorph.

　　It’s important to note that when watering, you must avoid allowing water that has flowed over diseased plants to come into contact with healthy ones. Otherwise, the disease could easily spread to other robust plants, potentially causing widespread plant death within the greenhouse. At the same time, we would like to remind vegetable growers that when transplanting chili peppers, they should apply bio-organic fertilizers (such as Jiji Kangjun 968) directly into the planting holes. The beneficial microorganisms in these fertilizers will multiply and thrive in the soil, and their effectiveness will not diminish over time.

　　Pepper plants are prone to leaf drop.

　　Peppers suffer extensive leaf drop due to disease infections; in severe cases, entire plants can become completely bare, with no leaves left on the branches. Without leaves, the plants are unable to carry out photosynthesis, eventually leading to exhaustion and death, resulting in significant yield reductions. Recently, during a visit to pepper greenhouses in Jitai Town, Shouguang City, many vegetable farmers reported precisely this situation. Because they couldn't correctly identify the diseases, they ended up using inappropriate treatments, which led to poor control and prevention results. To help farmers better manage these issues, the reporter has summarized four common diseases that cause severe leaf drop in peppers—information that vegetable farmers may find useful as a reference.

　　1. Pepper leaf blight. The most distinctive feature of this disease is its upward progression—from bottom to top. The lesions are grayish-white with a perforated center. In the later stages of the disease, if you gently shake the base of the stem, the leaves will fall off with a rustling sound, leaving behind a “bare stem.” To control and prevent this disease, it is recommended to spray a solution consisting of 10% difenoconazole diluted at 1,500 times or 20% thiacetam 600 times, or 20% Guanlv (mefenoxam + copper resinate) diluted at 800 times.

　　2. Bacterial leaf spot of peppers. This disease has been occurring more frequently recently, primarily affecting the upper leaves. In the early stages of infection, small yellow-green, water-soaked spots appear on the leaves; later, these lesions turn rust-colored and become thin and brittle as the mesophyll tissue is lost, leaving only the epidermis. The disease develops rapidly under conditions of high temperature and high humidity, leading to severe leaf drop in the later stages. In the Qingzhou area of Shandong Province, vegetable farmers commonly refer to this disease as “bacterial yellow shoot.” For prevention and control, spray with a 600-fold dilution of 2% Kasumin (kasugamycin) plus a 4,000-fold dilution of 72% agricultural streptomycin, or a 1,000-fold dilution of 20% chlorothalonil, or a 750-fold dilution of 33.5% Jingguojing (quinoxine copper).

　　3. Pepper powdery mildew. Powdery mildew is relatively easy to identify: at the onset of the disease, white powdery spots appear on the leaves; later, these spots expand into large patches that cover the entire leaf surface, causing severe leaf drop in the plants. To control and prevent this disease, you can spray the plants with a 1,000-fold dilution of 25% ethirimol or a 1,000- to 1,500-fold dilution of 30% azoxystrobin aqueous suspension.

　　4. Pepper white star disease. The key identifying feature of this disease is that the lesions on the leaves are nearly circular, with small white spots that resemble scattered white stars. In the later stages of the disease, extensive leaf drop occurs. To control and prevent this disease, you can spray a 500-fold dilution of 12% copper resin acid emulsifiable concentrate or a 300-fold dilution of 14% cuprous ammonium aqueous solution.

　　Pepper stem rot is relatively common.

　　In recent years, during bell pepper cultivation, the most troubling issue for vegetable farmers has been the phenomenon of stem rot and plant death that occurs when winter temperatures drop. In the early stages of the disease, lesions typically appear on one side of the main stem, near the branching points in the lower to middle sections, characterized by brownish decay. If left untreated, the lesions quickly spread around the entire stem, eventually causing the inside of the stem to rot and leading to plant death—severely impacting farmers' economic returns.

　　This phenomenon is primarily caused by three diseases: first, phytophthora blight; second, sclerotinia stem rot; and third, bacterial soft rot. These three diseases can be distinguished by the following symptoms: In the early stages of phytophthora blight in peppers, lesions appear as water-soaked spots, which later develop into brown or dark-brown stripes that encircle the epidermis. Above the affected area, branches and leaves gradually wilt. When field humidity is high, a white mold layer forms on the diseased parts, accompanied by a faint odor. Sclerotinia stem rot initially manifests as light-brown, water-soaked spots that turn to brownish-black and rapidly encircle the stem, then spread both upward and downward. Under high humidity conditions, a white, cotton-like mycelium develops on the surface of the infected area. Later, the bark of the stem rots away, with no odor; after drying, the affected area turns grayish-white. Bacterial soft rot initially appears as dark-green, water-soaked spots, which then turn brown and become soft and rotten, emitting a foul odor.

　　In recent years, Master Zhang has also developed an effective method for preventing and controlling stem rot and plant death—essentially “performing surgery” on the plants. In the early stages of the disease, as long as the rot hasn’t spread to half the circumference of the stem, this approach can save the plant with a success rate of nearly 90%. The specific procedure involves using a blade to carefully remove the rotted portion of the plant. Then, a paste is prepared by mixing fruit-setting agent with methyl tobuazin and DT, and this paste is applied to the cleaned-out area. It’s crucial to thoroughly clean out the diseased tissue; after application, a tumor-like growth will develop on the stem, but this won’t affect the plant’s normal growth. Master Zhang says that every year during this season, he spends four or five consecutive days lying down inside the greenhouse, meticulously searching for and treating any areas of rot. While performing these “surgical” treatments on individual plants, he also sprays the entire greenhouse with fungicides to eliminate pathogens and prevent further spread of the disease. If the type of disease has already been identified, treatment can be tailored accordingly—details on this are not repeated here. However, if the exact disease cannot be determined, a combination of chlorothalonil or pyraclostrobin with either Bacillus subtilis or kasugamycin can be used for prevention and control.