How is non-polluting control of pepper Phytophthora blight carried out?

I. Field damage symptoms

The peak incidence of Phytophthora blight in sweet (hot) peppers grown in open fields is from mid-July to the end of August. It is a fungal disease, and the incidence rate in vegetable fields is above 85%. The pathogen has a short incubation period, infects quickly, and spreads rapidly. In mild cases, yield is reduced by 30%; in severe cases, large areas of plants die, with a plant death rate of 20%-80%, or even total crop loss, causing devastating disaster. Symptoms: In affected areas there are obvious primary infected plants. In the early stage of the disease, plants wilt, while leaves and fruits do not drop and do not change color. Upon careful observation, it can be found that the stem base of the plant turns brown around its circumference for a week, and may even become constricted. In severe cases, the upper stems, leaves, and fruits all become infected. When humidity is high, the fruits produce a white mold layer, and after drying and shriveling they still hang on the branches. After leaves are severely infected, dark green water-soaked lesions rapidly expand and cause soft rot; after drying, the lesions turn light brown, and at this time fruits and leaves tend to drop. Stems are prone to first develop disease at the branching area near the roots, and in severe cases the cortex softens and rots, making them easy to break.

II. Causes of the disease

1. Climatic conditions are the determining factor for the occurrence and epidemic of Phytophthora blight. When temperature conditions are suitable, generally with an average daytime temperature of 25°C and a nighttime temperature of 11°C, and with continuous rainy days or foggy or dewy weather, the field is hot and humid, and sweet (hot) pepper Phytophthora blight is likely to occur sharply and spread rapidly, leading to a major epidemic.

2. Poor varietal resistance.

3. Seeds or seedlings carry the pathogen. Seeds or seedlings carrying the pathogen are the main source of primary infection. After diseased seedlings are transplanted, the pathogen spreads to other plants with soil moisture; it can also infect other plants through cultivation and rainwater, forming primary infected plants and expanding infection to nearby plants.

4. Severe continuous cropping and return cropping. Continuous cropping and return cropping cause the pathogen that overwinters in the soil and on diseased residues to continue infecting pepper plants the following year.

5. Improper plot selection. Low-lying plots with poor drainage and heavy clay soil are conducive to the occurrence and epidemic of Phytophthora blight.

6. Improper cultivation management. Excessive application of nitrogen fertilizer, high planting density, poor land preparation quality, untimely intertillage, severe weed infestation, weak seedling growth, flood irrigation, water accumulation in the field, and failure to prevent the disease in time are also important factors in disease occurrence.

III. Non-polluting control

Implementing the policy of "prevention first, integrated control" to control diseases, insects, and weeds in sweet (hot) peppers is a key strategy for non-polluting vegetable production. In integrated control, agricultural control should be the foundation, and chemical control, biological control, physical control, and other measures should be reasonably applied according to time and local conditions.

(I) Agricultural control

1. Select good disease-resistant varieties. On the premise of selecting varieties that sell well and are suitable for local planting, varieties with high yield, good quality, resistance to diseases and insects, and strong stress resistance should be planted. For example, excellent varieties such as Chitianjiao No. 1 and Chijiaowang are moderately resistant to Phytophthora blight and Fusarium wilt, but varieties resistant to Phytophthora blight are somewhat weaker in resistance to downy mildew and powdery mildew.

2. Correct plot selection. Select plots with a good regional ecology, far from pollution sources, clean air and irrigation water, convenient drainage and irrigation, and deep, loose, fertile loam or sandy loam soil with a pH value of 6.0-7.5. The previous crop should be wheat, soybean, or corn stubble with autumn plowing. Plots whose previous crop was solanaceous fruit crops, potatoes, or cucurbit crops must not be selected, and particular attention should be paid to avoiding plots where long-residual pesticides were used the previous year.

3. Cultivate disease-free strong seedlings. (1) Seed disinfection: soak seeds in warm water at 52°C for 15 minutes, or pour 1 kg of seeds into 80 mL of 98% concentrated sulfuric acid, stir thoroughly, and let stand for 5-6 minutes. After rinsing with clean water, soak for 4-8 hours to promote germination and sow. (2) Seedling raising in disease-free soil: select fertile soil that has not been planted with solanaceous fruit crops, cucurbit crops, or potatoes, and mix it evenly with fully decomposed farmyard manure as seedling soil to cultivate disease-free seedlings. (3) Chemical treatment of seedbed soil: for each square meter of seedbed, mix 1 g of Lüheng No. 1 and 5 g of 50% thiram with 20 kg of fine soil, then spread 1/3 on the bed surface and use the remaining 2/3 as covering soil after sowing. (4) After emergence, spray the seedbed with 40% fosetyl-aluminum 300-fold solution or 25% metalaxyl 800-fold solution. 10 days before transplanting, spray twice with 50% metalaxyl-copper 500-fold solution to prevent the pathogen from entering the field.

4. Improve cultivation measures and strengthen field management. (1) Autumn plowing and land preparation, with a plowing depth of 18-22 cm, and level and fine harrowing. (2) Scientific fertilization. The fertilizer requirement characteristics of sweet (hot) peppers are potassium ≥ nitrogen > phosphorus. For every 1000 kg of marketable peppers produced, 3.54 kg of nitrogen, 1.03 kg of phosphorus pentoxide, and 3.38 kg of potassium oxide need to be absorbed. High-quality farmyard manure should be used mainly as base fertilizer, potassium fertilizer should be increased, timely topdressing should be applied to promote plant growth and fruit development, and trace element fertilizers should be used as needed. (3) Adopt plastic film mulching and high-ridge cultivation. (4) Strengthen field management, carry out timely deep plowing and weed control, and enhance pepper plant resistance. Diseased plants should be pulled out in time and taken outside the field for destruction, and diseased planting holes should be covered and leveled with quicklime for sterilization. (5) Master the cultivation characteristics of the planted varieties and achieve good varieties with good methods.

(II) Chemical control

1. Focus on prevention, that is, spray protective agents before the disease occurs, with emphasis on the root and stem base. It is recommended to use Lüritong 600-800-fold solution and apply it 2-3 times; it has both protective and therapeutic effects and can basically ensure that the disease does not occur.

2. For diseased fields, spray imported Previcur 500-fold, or use 64% oxadixyl-mancozeb 400-fold solution, or 58% metalaxyl-mancozeb 500-fold solution, or 25% fosetyl-aluminum 300-fold solution, alternating pesticides to prevent the pathogen from developing resistance.

3. Master the pesticide pre-harvest interval. In summer and autumn, pesticides must not be used 8-10 days before fruit harvest, or marketable peppers may be harvested only 10 days after pesticide application.