A Detailed Guide to the Latest Control Methods for Walnut Brown Spot Disease
Walnut brown spot disease mainly damages leaves and young shoots. In the early stage of leaf infection, grayish-brown round to irregular lesions appear, and later black dots form on the diseased parts. Severely affected leaves wither and scorch and drop early. After young shoots are infected, the lesions are dark brown, long oval, and slightly sunken. Diseased seedlings often form dead tops. Now let us take a look at the control methods for walnut brown spot disease!
Symptoms
The diseased leaves of walnut brown spot disease mainly harm walnut leaves, new shoots, and fruit. On young leaves, the lesions are brown and polygonal; on older leaves, the lesions are round, grayish-brown in the center, brown at the edges, sometimes with a yellow halo on the outer margin, and the grayish-brown central part sometimes forms perforations. In severe cases, the lesions join together. Sometimes lesions also appear on the petioles. On twigs, the lesions are elongated, brown, and slightly sunken; in severe cases, the lesions surround the branch and cause the upper part to die. When fruit is affected, small, slightly raised brown soft spots first appear on the epidermis, then rapidly expand, gradually become sunken and black, with water-soaked halo lines on the outer margin; in severe cases, the kernel turns black and rots. When old fruit is invaded, only the outer pericarp is affected.
Occurrence Pattern
The pathogen of walnut brown spot disease overwinters as conidia on damaged leaves and twigs. After overwintering, the diseased leaves and twigs can still produce spores under suitable temperature and humidity conditions and spread with wind and rain. Fruit is easily infected by the pathogen before shell hardening, and the disease is severe when there is heavy rain in late spring and early summer. The severity of plant disease is related to humidity, and it spreads rapidly after rain. The incubation period of this pathogen is 5-34 days on fruit and 8-18 days on leaves. The leaf expansion and flowering stages are the most susceptible. In central Hebei, the peak disease period is from late July to mid-August, while in Shandong it generally begins from mid-to-late May.
Control Methods
1. Field management: Before the spring rains arrive, thoroughly clean the walnut orchard, promptly remove diseased branches and leaves, and bury them deeply or burn them. At the same time, strengthen comprehensive management of walnut cultivation, enhance tree vigor, and improve disease resistance. In particular, attention should be paid to improving the soil, increasing fertilizer application, and improving ventilation and light conditions.
2. Chemical prevention: Before the onset of walnut brown spot disease, use "Aolike-Liangguoan" diluted 300 times and spray it, applying once every 15 days, together with "Wofengsu" diluted 600 times and sprayed, applying once every 7 days. This can relatively effectively prevent the occurrence of walnut brown spot disease.
2. Chemical treatment: When the disease is mild, use "Aolike-Liangguoan" diluted 300 times and spray it, applying once every 10-15 days. When the condition is severe, dilute it 200 times and spray once every 7-10 days. If the condition is severe, "Wofengsu" is needed, diluted 600 times and sprayed, applying once every 3 days. At the same time, strengthen orchard management, increase organic fertilizer application, improve tree disease resistance, pay attention to drainage after rain, and reduce orchard humidity.