Techniques for preventing and controlling black spot of walnut

Technology for preventing and controlling walnut black spot

With the adjustment of agricultural structure and the promotion of farmers 'income increase, walnut planting has been developed in a large area in Taocheng District, Hengshui City, Hebei Province, and Lvling walnut was first introduced in 2014. Now walnut trees have entered the fruiting period one after another, but in the production found that the variety of bacterial black spot is more serious. Walnut black rot, also known as black rot, is a bacterial disease, mainly harmful to walnut fruit and leaves, fresh spots edge disease healthy junction has bacterial pus phenomenon.

1 Symptoms of harm

The disease mainly damaged walnut fruit, leaves, tender, bud and female inflorescence. Among them, fruit damage is the most serious, and the serious damage can reach 80%. Small and slightly raised brown soft spots appeared on the fruit surface after infection. The soft spots gradually enlarged, sank and blackened, and there was a water-soaked halo around them (Fig. 1). Young fruit disease, the pathogen attack to the kernel, so that the kernel rot. When the fruit grows to medium size, the disease is limited to the exocarp, but the nucleolus growth is hindered and shriveled after harvest. The fruit decays from outside to inside and is often called "walnut black." Leaf infection, first in the vein and vein bifurcation appeared brown spots, after expansion, the spot was mostly square or polygonal, late, the center of the spot was gray or perforated. In severe cases, the disease spots expand continuously, the center falls off into perforations, or the whole leaves wither and fall off (Figure 2). Petiole, tender shoots and branches on the disease spot fusiform or irregular, black, slightly concave, serious when the circle around the branches, so that branches die [Jishan Huayao].

Fig. 1. Walnut fruit damage

Fig. 2 The injured leaves of walnut

2 Rules of incidence

The pathogen overwintered in diseased branches, canker spots, bud scales and residual diseased fruits. In the spring of the following year, the pollen carried by bacteria was spread to leaves, fruits and twigs by rain or insects, and reinfected many times. Germs can attack pollen, so pollen can also spread germs. Bacteria invade through wounds, fur holes or stigmas. The incubation period of the pathogen is generally 10~15 days. The incidence and degree of the disease are closely related to rainfall. In rainy years and seasons, the onset is early and severe. In Taocheng District of Hengshui City, Hebei Province, the disease usually begins in the middle and late May, and the peak period is from June to July. The walnut planting density is high, the crown is dense, the ventilation and light transmission are poor, and the disease is serious. Generally, the weaker the tree, the worse the disease.

3 Methods of Prevention

(1) Select disease-resistant varieties, select reasonable planting density, shape and prune in time, make the tree structure reasonable, and maintain good ventilation and light transmission conditions.

During pruning, overlapping branches, cross branches, dead branches, diseased branches and some male flower branches are mainly thinned, ventilation and light transmission conditions of crown and forest land are improved, and disease occurrence is reduced.

(2) Strengthen underground management, apply more organic fertilizer or special fertilizer for fruit trees, and increase foliar fertilizer to enhance tree vigor. Cut off and remove diseased branches, diseased leaves and diseased fruits in time. Peel taken off after walnut harvest shall be burned or buried deeply to reduce the base number of pathogenic bacteria.

(3) timely control of walnut moth and other pests, fruit picking as little as possible to use sticks to beat, avoid damage to branches, reduce wounds, reduce the chance of infection.

(4) Chemical control: carefully spray 3~5 Baume degree of sulfur mixture once in the first and middle of March before germination, spray 1∶2∶200 Bordeaux mixture or 70%(mass fraction, the same later) methyl thiophane WP 800~1 000 times solution or 50% Tuijunte WP 600~800 times solution or agricultural streptomycin 50 mg/kg solution, 70% methyl thiophane + agricultural streptomycin sulfate. 5-7 Spray every 15 days in June, spray 2 to 3 times, alternate use, in case of resistance.