Robinia pseudoacacia dry rot

Symptoms: the disease harms the branches of young trees to big trees, causing the branches to wither or the whole plant to die. Big trees occur mainly at the base of the stem and a few at the bifurcations of the upper branches. The base of the tree was killed, there were no obvious symptoms on the outside, the interior of the bark was discolored and rotten, there was a bad smell, and the surface of the xylem produced brown to dark brown irregular spots. The disease spot continues to expand, encircling the tree trunk for a week, causing the branches above the disease spot to die, and the leaves yellowing and withering. The main stem of the branch or young tree was damaged, and the diseased tissue rotted in the form of water stains, resulting in obvious ulcer spots, slightly sunken, and the edges were purple-brown. With the expansion of the disease spots, the parts above the disease spots soon withered.

Pathogen: pathogenic Phytophthora cinnamon (PhytophththoracinnamomiRands), belonging to the subphylum flagellum, oomycetes, downy mildew fungi.

The law of the disease: the pathogenic bacteria often invade from the dry base, and some begin to develop the disease from the cadres. The wound of underground pests is the main way of infection. Wounds caused by high soil water content or strong winds, as well as mechanical injuries caused by human and animal activities, can be ways of infection. The epidemic period of the disease is from May to September. When the temperature is more than 25 ℃ and the relative humidity is more than 85%, the disease spot expands rapidly.

Prevention and control: ① low-lying water or close to the source of water, are not suitable to plant Robinia pseudoacacia. Or do a good job of trenching and drainage to reduce soil moisture. ② removes dead plants or piles in time, and the soil is disinfected with 5% formaldehyde solution. ③ trunk whitening and sowing with copper sulfate, ferrous sulfate or lime on the soil surface have a certain control effect. The early lesion of ④ is removed by surgery or perforated or cut with a knife, and then smeared with 25% carbendazim 30-50 times or 50% carbendazim 60 times, 2-3 times, has an inhibitory effect on the disease. ⑤ irrigated soil with 2000-fold solution of deltamethrin to control underground pests.