Prevention and control of blight of Castanea mollissima

Chestnut blight, also known as chestnut dry blight and canker, is a worldwide disease. Seedlings and fruiting trees can be infected, the light ones lead to the decrease of afforestation survival rate and the amount of fruit, the heavy ones lead to the failure of afforestation or the failure of the whole chestnut forest. In order to change the previous situation of single forest species and actively develop economic forest species in Xitaoyuan Forest Farm of Mingguang City, more than 300 mu of Castanea mollissima forest has been built in Dashatang area since 1998 and grafted in the spring of 2000. During the introduction of scion, the blight of Chinese chestnut was brought into the country inadvertently. In late April 2001, many plants were found to die in the grafted chestnut forest, some of them had a large number of dead branches, and some of the branches sprouted late. the leaves grow yellow, some of the leaf edges are scorched, and the tree growth is weak. Through the field investigation of Castanea mollissima in the first ten days of May 2001, it was found that there were irregular black-brown disease spots like shark skin at the base of the branches, the acicular orange-yellow uplift on the surface, and the whole disease spot was slightly sunken downwards. It was found that the disease spot had been hanging around the branch rod for a week at the base of the newly withered branch. Lifting the brown spot, you can see that the internal tissue is reddish brown, rotten in the shape of water stains, and has the smell of wine lees. There are orange filaments on the disease spots of some dead branches, that is, the conidia angle of the pathogen. Some lesions have small black tumor-like dots under the skin, that is, the daughter of the bacteria. It is confirmed by further laboratory examination and consulting relevant data that this is chestnut blight, the pathogen is Chestnut Phytophthora, belonging to ascomycetes, Choriaceae, saprophyllaceae and inner crustaceae.

I. occurrence regularity and symptoms

The pathogen is a facultative parasite, overwintering in the diseased tissue with mycelium, ascomycete and conidia, and the conidia and ascospores can be infected. In December every year, ascospores mature one after another and spread outward through human, insect, bird, wind or rain to invade new host wounds. From late March to April in the second year, when the temperature reached more than 4-5 ℃, the pathogen began to grow and the host began to become sick. Due to the low temperature at this time, the development of the disease spot is slow, when the temperature rises to 20-30 ℃, the expansion of the disease spot is accelerated, the disease is aggravated, and the black nodule-like particles are produced under the bark of the disease spot, which is the seed seat of the pathogen. The top of the back seat breaks through the skin, and in case of overcast and rainy weather, a strip of orange bearded conidia horn is extruded from the conidium. The cylindrical, single-celled conidia were released into the asexual generation of cyclic infection. Finally, the ascomycetes turn orange-red to sauce-red, and a bottle-shaped, black, dark upper and light lower ascomycetes are gradually formed, resulting in rod-shaped ascospores and releasing ascospores. A feathery fan-shaped mycelium can be seen between the diseased bark and xylem, and the color is dirty white, yellow or yellowish brown. When the temperature dropped below 10 ℃, the plaque developed slowly and finally stopped and entered the overwintering period.

II. Prevention and control measures

The main results are as follows: 1. Completely remove the dead plants and branches, plane the dead plants from the roots, and disinfect the holes with quicklime to cut off the dead and some branches with large disease spots and some weak branches with poor growth.

2. Scrape off the smaller disease spots on the thicker branches with a knife, and smear the scratched parts and cut off branches with 0.5 Baomedushi sulfur mixture, as well as other wounds with mechanical injuries.

3. Spray immediately with 500 times of dimethazone, once every 15 days, for 3 times in a row. After application, it was observed that Dixong had obvious therapeutic effect on chestnut blight, no plants died of chestnut blight were found in the controlled chestnut forest, and the branches infected by the blight were rarely seen, and the whole chestnut forest grew vigorously. In the chestnut forest without control, the plant mortality rate was as high as 20%, and disease spots of 1-2 cm in size were found on the plant, and the overall health status of chestnut was poor.

4. In the whole growing period of Castanea mollissima, once a pest is found to be harmful to tender shoots and leaves, dimethoate or enemy killing will be used immediately to protect leaves and branches from damage.

5. Loosen the soil once in early spring, and turn the soil from the pole base outward from shallow to deep so as not to harm the root of the chestnut tree. Combined with urea or compound fertilizer 250-500 kg per plant, or cake fertilizer 1-1.5 kg, or farm fertilizer 2.5-3.5 kg, plus 50 g carbofuran, to promote root growth and tree nutrition supply, enhance tree potential, and kill soil pests such as grubs.

6. Strengthen tending and management, weed in time, put an end to grass and famine, implement forest-grain intercropping, timely drainage and irrigation, and apply 250 grams of available nitrogen fertilizer per plant in mid-June. It is forbidden for people and animals to enter the forest and destroy.

7. Eliminate other infected trees of Fagaceae near the chestnut forest and reduce the source of infection in the future.

8. Strengthen the quarantine work, select excellent and disease-resistant varieties to transform the chestnut forest, and soak the branches and plants with 180 times lime Bordeaux solution for reuse.

9. The young forest was loosened once before winter, and 1.5-2.5 kg of farm manure or 1-1.5 kg of cake fertilizer was applied to each plant to improve the soil structure, increase the soil fertility and the content of organic matter, provide sufficient nutrition for the growth of Chinese chestnut in the coming year, and cultivate the roots into a cone, remove them at the beginning of spring, reduce the chance of frost injury in the young forest, and spray 200 times lime Bordeaux solution once to protect the trees through the winter.

10. Before the chestnut germinated in early spring, the stone sulfur mixture of 2-3 Baumetu was injected once, and then 0.5 Baomedo stone sulfur mixture was used again after germination to protect the wound from infection and reduce the incidence of the disease.