What are the harmful symptoms of peanut brown spot? Detailed control methods

Peanut brown spot is a fungal disease caused by infection with Cercospora arachidicola of the subphylum Deuteromycotina. It harms peanut leaves, initially appearing as small chlorotic spots, which later expand into nearly round or irregular small spots. The lesions are larger and lighter in color than those of black spot disease, appearing dark brown or tea-brown on the upper leaf surface and brown or yellowish-brown on the underside, with a bright yellow halo around the lesions. Now let us take a look at the control methods for peanut brown spot!

Symptoms of peanut brown spot

Peanut brown spot mainly harms peanut leaves, initially appearing as small chlorotic spots, which later expand into nearly round or irregular small spots. The lesions are larger and lighter in color than those of black spot disease, appearing dark brown or tea-brown on the upper leaf surface and brown or yellowish-brown on the underside, with a bright yellow halo around the lesions. When humidity is high, a grayish-brown powdery mold layer, namely the pathogen's conidiophores and conidia, can be seen on the lesions. When petioles and stems are infected, the lesions are elongated-oval and dark brown.

Conditions for the occurrence of peanut brown spot

The pathogen overwinters on diseased residues as stromata, mycelial masses or ascocarps. In the following year, when conditions are suitable, it produces conidia, which spread through wind and rain to cause primary infection and reinfection. The hyphae extend directly into intercellular spaces and cells to absorb nutrients, generally without producing haustoria. The growth temperature range of the pathogen is 10-33°C, with the optimum at 25-28°C. In rainy and humid climates, the disease is severe. It occurs earlier, and young leaves are more severely affected than old leaves.

Control methods for peanut brown spot

1. Select relatively disease-resistant varieties such as Hua 39, 68-4, 8130, Luhua No. 11, Luhua No. 13, Luhua No. 9, Qunyu 101, P12, and Hua 17.

2. In the early stage of the disease, spray with 25% carbendazim · mancozeb wettable powder at 375-750 g/ha or 70% thiophanate-methyl wettable powder at 263-350 g/ha, once every 7 days for 2 consecutive applications, used alternately.

Symptoms and control of osmanthus brown spot

Symptoms and control techniques of jujube brown spot

With the gradual expansion of jujube planting area, the occurrence of diseases has also become increasingly serious. Among them, diseases such as jujube brown spot have seriously affected the yield and quality of long jujube, causing certain economic losses to fruit growers. This article summarizes the symptoms, occurrence patterns, disease conditions and control techniques of jujube brown spot for everyone's reference.

Harmful symptoms of jujube brown spot

This disease generally begins to show symptoms from the white-ripe stage (as early as early August), and does not occur before the white-ripe stage. The lesions mostly occur at the top or middle of the fruit. In the early stage, they are yellow or pale red, with irregular edges and irregular water-soaked small lesions, 3-5 mm in diameter, expanding slowly, with a very low occurrence rate. If rainfall occurs from late August to late September, diseased fruits appear in large numbers, the lesions expand rapidly, and the diseased tissue takes an inverted semicircular shape, extending 3-5 mm into the flesh. The boundary between diseased and healthy fruit is easy to peel away, and diseased fruits taste bitter, with a very high occurrence rate. The black-red lesions are neither raised nor sunken, and later measure 5-15 mm. Diseased fruits not falling off is a notable feature of this disease.

Occurrence pattern of jujube brown spot

The pathogen of jujube brown spot overwinters as mycelium, pycnidia and conidia on diseased shriveled fruits and dead branches. After the jujube trees sprout the following year, the conidia spread through wind, rain and insects, and invade through insect wounds, natural openings or directly penetrating the epidermal layer of jujube fruits. After flowering and in the early young fruit stage, the pathogen begins to infect but does not cause disease; after invasion, the pathogen remains latent. When the fruit approaches maturity and the sugar content of the flesh increases significantly, the latent hyphae rapidly expand and induce fruit disease. As the fruit matures and ages, the wax layer and cuticle of the peel thicken, air permeability weakens, and the respiration of the fruit itself strengthens. The fruit easily releases ethylene, promoting fruit softening and accelerating rotting. When humidity is high during the fruit ripening period, conidia are produced again in that year to reinfect the fruit. Through indoor and field artificial inoculation, it has been proven that the incubation period of the disease at this stage is only 2-7 d, so the disease develops rapidly.

Disease conditions of jujube brown spot

According to investigation and analysis, the occurrence of jujube brown spot is mainly related to rainfall, the use of gibberellin and tree vigor: (1) The disease is related to rainfall. The timing and severity of the disease are closely related to the number of rainfall events in that year and the relative humidity in the air of the jujube orchard. Rainy conditions during the fruit ripening period are an important trigger and also a necessary condition for the occurrence of fruit brown spot. In years with much rainy weather, especially from mid-June to early August, if there are many consecutive rainy days, the disease occurs early and severely; otherwise, it occurs late and mildly. (2) The disease is related to plant hormones such as gibberellin. Jujube fruit brown spot is a fungal disease, belonging to weak parasitic fungi. Because the use of plant hormones such as gibberellin increases yield and lowers the fruit-to-leaf ratio, it leads to nutritional deficiency in the fruit and decreased immunity, which is the internal cause of brown spot occurrence. (3) The disease is related to tree vigor. Weak tree vigor leads to early and severe disease, while strong tree vigor leads to late and mild disease. Field investigation found that jujube orchards located at the edge of the eastern hillside, because of higher terrain, long-term irrigation with well water, poor orchard sanitation, and intercropping of melons, beans and vegetables between jujube rows, had thin leaves, pale leaf color and weak tree vigor, so the disease occurred early and severely.

Control measures for jujube brown spot

(1) Agricultural control. Do a good job of orchard sanitation, remove fallen shriveled fruits and bury them deeply. For severely affected jujube orchards or plants, in combination with pruning, carefully cut off dead branches and diseased pest branches and burn them in a centralized manner to reduce the source of disease. Strengthen comprehensive management, apply more organic fertilizer and phosphorus-potassium fertilizer, strengthen tree vigor, and improve disease resistance. Plant low-stalk crops such as peanuts and beans between jujube rows, do not intercrop tall crops such as corn, maintain ventilation and light transmission in the jujube orchard, reduce air humidity in the orchard, and reduce disease occurrence. (2) Spray protection. 5-10 d before sprouting, spray the whole orchard with 3-5°Be lime sulfur mixture to eliminate overwintering pathogens on the tree body. In the young fruit stage, 3-5 d before rainy weather, spray 25% triadimefon wettable powder at 2000-3000 times dilution 1-2 times in the orchard, or spray 50% chlorothalonil wettable powder at 600-800 times dilution once every 10-15 d.