Symptoms and control of bacterial black spot of walnut

   1. Distribution and occurrence characteristics are widely distributed in Hebei, Shandong, Shanxi, Liaoning, Henan, Jiangsu, Zhejiang, Sichuan, Yunnan, Shanxi, Gansu and other walnut producing areas. Infection usually begins in the middle and last ten days of May. The pathogenic bacteria overwintered in the diseased spots on the diseased shoots or in the diseased buds. In the spring of the following year, the bacteria spread to the leaves, fruits and twigs by wind and rain splashing, and the bacteria could infect the flower organs. Therefore, pollen can also carry bacteria, and insects are also the carriers of bacteria, which are invaded by stomata, lenticels, nectaries and various wounds. Under the condition of sufficient humidity, the temperature could infect leaves in the range of 4 ~ 30 °C, and the fruit could be infected at 5-27 ℃. The incubation period was also different in different parts, 5-34 days on fruit and 8-18 days on leaves.

   2, pathogen and symptoms of walnut bacterial black spot pathogen is yellow spores rod-shaped bacteria, which mainly damage fruits, but also damage leaves, shoots and branches. After the fruit was damaged, the small black-brown oil-stained spots were produced on the green pericarp, which gradually expanded into a round or irregular shape, without obvious edges, the disease spot was deeply sunken in severe cases, the whole fruit became black and rotten, and the damage rate was 30% to 70%. In severe cases, it can reach more than 90%, the nucleolus is withered, the weight is reduced by 40% to 50%, and the quality of nuts is reduced.

After the    leaves were infected, the leaves were brown on the front, light brown on the back, and shiny oily. The periphery of the disease spot is a translucent yellow halo ring, and in severe cases, the disease spot is connected into a piece, resulting in fruit shedding. Inflorescences produce dark-brown watery spots after invasion.

The pathogenic bacteria of    overwintered in diseased branches or shoots and spread to fruits or leaves through wind and rain and insects in the following spring and invaded from wounds or natural stomata. The pathogen can also spread with pollen, often with the occurrence of walnut limb moth. Rainy or humid weather in summer is conducive to bacterial infection, and the orchards with high planting density, closed canopy and poor ventilation and light transmission are seriously affected.

   3. Prevention and control methods

  ① Juglans mandshurica is more resistant to black spot, so it can be used as rootstock.

  ② removed the source of bacteria, combined with pruning, cut off diseased branches and fruit, and picked up the fallen fruit on the ground and burned it centrally, so as to reduce the source of bacteria in the orchard.

  ③ chemical control. Spray 3-5 Baumedo stone-sulfur mixture once before germination to kill overwintering bacteria; spray Bordeaux solution of 1: 0.5: 200 (copper sulfate: lime: water) during the growth period, or 50% methyl topiramate 500 times 800 times. Usage: spray, once before flowering, once after flowering and once in young fruit stage. Spray 0. 5% during the growing period. 4% copper sulfate has good effect and is not easy to cause drug damage.