Detailed Explanation of Pepper Pest and Disease Control Methods and Technical Key Points

Pepper Phytophthora Foot Rot

PepperPhytophthora foot rot, also known as pepper basal rot, rapid decline disease, and black water disease, is the most important pepper disease in pepper-growing regions worldwide. It was first discovered in 1926 in Sundara Man in India, and subsequently occurred in Indonesia, Malaysia, Cambodia, and some countries in South America and Africa. In Sarawak, Malaysia, it broke out in epidemics multiple times, causing massive pepper yield reductions and forcing severely affected pepper gardens to be abandoned. In China's Hainan Province, pepper Phytophthora foot rot first reached epidemic proportions over a large area in 1960, destroying large tracts of pepper gardens; the pepper planting area did not recover until 1969, but from 1970 to 1972 it was again damaged by pepper Phytophthora foot rot, and 78% of pepper gardens were destroyed by this disease, causing serious losses to China's pepper production. This disease also occurs in pepper-growing areas of Guangdong, Yunnan, and Guangxi.

Symptoms: The root system, main vine base, branches and vines, leaves, flowers, and fruits of pepper plants are all affected. Damage to the main vine base (called the pepper head) causes the greatest harm, often leading to wilting and death of the entire pepper plant. When the already suberized part of the main vine base 20 cm above and below the ground surface is affected, there are no obvious external symptoms in the early stage of infection; when the outer bark is scraped away, the inner cortical layer is seen to have turned black, and the xylem is light brown. A longitudinal cut of the main vine reveals blackened xylem vessels, with brown streaks spreading upward and downward, and the boundary between diseased and healthy tissue is indistinct. In the later stage, the outer bark turns black, rots, and falls off, and a black liquid flows out from the rotting xylem (hence the name black water disease), and the central column splits into a bundle of loose vessel fibers. When diseased plants are dug up and examined, the root system near the infected underground main vine is seen to be diseased, blackened, and rotting, gradually spreading toward the root tips, while other roots in the lower layer are not yet affected. This is clearly different from the symptoms of pepper water damage and fertilizer damage, which begin with necrosis at the root tips and later cause large roots to rot. In plants where the main vine base is diseased and rotting, the entire leaf canopy becomes lusterless, the leaf color is dull, and the plant appears dehydrated, with leaves wilting and dropping. If the weather is dry and hot, such diseased plants may suddenly wilt green within a few days, and finally turn black together with the tender vines; the dead tender vines may drop off segment by segment.

Leaves on the lower branches and vines of the plant are affected first, starting as light brown or grayish-black water-soaked spots. The spots rapidly expand into dark brown, circular lesions, with edges spreading radially and an indistinct outline. In humid conditions, a white mold-like substance, namely the pathogen's mycelium and sporangia, grows on the underside of diseased leaves. In dry weather, the mold-like substance disappears, the lesions turn grayish-brown, and the diseased leaves eventually drop off. When tender branches and vines are infected, the cortex produces water-soaked, dark green diseased marks, and in severe cases they drop off segment by segment. When inflorescences and fruit spikes are infected, the disease generally begins at the tip, producing water-soaked spots that later turn black and dry up.

Pathogen: The pathogen is a fungus, with the scientific names Phytophthora capsici and Phytophthora parasitica. It belongs to the subdivision Algal Fungi (Phycomycotina), order Peronosporales. In China's pepper-growing areas, the occurrence rates of these two Phytophthora species are roughly equal, and both are major pathogenic fungi of pepper Phytophthora foot rot.

Infection cycle: Both Phytophthora pathogens can survive in the diseased tissues of pepper plants and in the soil. Infested soil, diseased (dead) plant residues and the diseased remnant tissues of other host plants can all provide primary infection sources. The pathogen is mainly transmitted by running water (stream water, irrigation water) and by wind and rain; humans, livestock, farm tools, seedlings, and giant African snails can also carry the pathogen and transmit the disease. The germ tubes of sporangia or zoospores can invade through natural openings or wounds of the host, and can also directly penetrate young tender tissues. When inoculated onto suberized pepper main vines, the incubation period is 15 to 20 days; when inoculated onto tender leaves or tender vines, the incubation period is 2 to 5 days.

Epidemic patterns: The epidemic of pepper Phytophthora foot rot is closely related to the soil type, topography and terrain, cultivation measures, and rainfall conditions of the pepper garden in that year. Generally, in places with heavy clay soil, poor drainage, or low-lying waterlogged areas, the disease occurs earlier and is more severe; conversely, in sandy soil with good drainage, the disease is milder. Pepper gardens that are too concentrated and lack shelterbelts, or where the pepper head is injured by twisting when changing posts and tying vines, or where weeding is done in diseased gardens on rainy days, or where diseased plants are not removed promptly and preventive spraying is not carried out, are prone to epidemics in rainy years, especially in years with many typhoons. The occurrence and epidemic of this disease within a year can be roughly divided into the stage of central diseased plants (areas), the stage of general spread, the stage of severe disease with massive death, and the stage of declining epidemic speed. The disease begins to appear on a small number of plants from March to April each year, and August to November is the epidemic period of the disease. Control methods: To control the epidemic of pepper Phytophthora foot rot, comprehensive disease control measures combining agricultural measures and chemical control must be adopted.

1. Agricultural preventive measures

(1) Site selection and garden establishment. New pepper gardens should carry out proper land planning and basic farmland construction. That is, choose land with good permeability and easy drainage for planting pepper; pepper gardens should not be too concentrated, and the area of each pepper garden should preferably be 3 to 5 mu, with shelterbelts planted around them; terraces or contour beds should be built in the garden, and drainage ditches around the garden and small drainage ditches between rows should be dug to prevent the pathogen from spreading via running water; in low-lying areas, soil mounds should be built for planting pepper.

(2) Use disease-free seedlings. Do not cut vines from diseased gardens as cuttings, and seedlings should be raised in disease-free plots.

(3) Strengthen tending and management. Weeding and fertilization should be carried out on sunny days, and care should be taken not to injure the pepper head and root system; properly prune branches and vines close to the ground to reduce humidity at the pepper head and reduce infection of lower leaves; promptly earth up so that the pepper head is above the ground, preventing water accumulation at the pepper head and invasion by the pathogen via running water; promptly remove dead branches and fallen leaves and diseased and dead pepper heads in the garden; do not apply excessive nitrogen fertilizer; plant cover crops between rows in the pepper garden or use dry grass as dead mulch to reduce pathogen transmission by running water and splash dispersal during rain.

(4) Keep timely track of the disease situation and isolate diseased areas well. During the disease epidemic season, especially during typhoon and rain periods, assign dedicated personnel to inspect the disease situation in each garden. Once diseased plants are found, promptly apply chemicals for control, and seal off and isolate the diseased area, prohibiting entry by people and livestock. Farm tools used in the diseased area should not be brought to disease-free gardens. When carrying out field management, start with disease-free gardens and then diseased gardens. On rainy days when the soil is wet, stop agricultural activities such as weeding and fertilization in diseased gardens to reduce human-mediated transmission.

2. Chemical control

In the early stage of disease onset, spray 1% Bordeaux mixture or 40% fosetyl-aluminum wettable powder at 100 times dilution on the central diseased area (plants) and surrounding plants, and spray the inter-row soil of the diseased area with 1% copper sulfate solution or 1% Bordeaux mixture. Promptly dig out and remove diseased and dead plants, transport them outside the garden and burn them, and the soil of the diseased planting holes should be dug open and exposed to the sun or drenched with 1% copper sulfate solution for disinfection.