Control Methods for Chestnut Blight in Chestnut Cultivation
Chestnut blight, also known as chestnut dieback and canker, is a worldwide disease. Both seedlings and fruiting trees can be infected; in mild cases it reduces afforestation survival rates and yields, while in severe cases it causes afforestation failure or total crop loss of an entire chestnut grove. In order to change the previous situation of a single forest type, Xitaoyuan Forest Farm in Mingguang City actively developed economic forest species. Starting in 1998, in the Dashatang section of the farm headquarters work area, more than 300 mu of chestnut forest was established, and grafting was carried out in the spring of 2000. When introducing scions, chestnut blight was inadvertently brought into the area. In late April 2001, many dead plants were found in the grafted chestnut forest; some plants had extensive dead branches and trunks, while others had branches that sprouted late, with yellowing leaves, partially scorched leaf margins, and weakened tree vigor. Through on-site investigation of the chestnut plot in early May 2001, it was found that the base of poorly growing branches and trunks had irregular blackish-brown lesions resembling shark skin in patches, with the surface densely covered in needle-head-shaped orange-yellow raised bumps, and the entire lesion slightly sunken downward. At the base of recently dead branches and trunks, lesions were found to have girdled the branch or trunk for 1 full circuit. Lifting the brown lesions revealed reddish-brown internal tissue, water-soaked and rotting, with a sour mash odor. On some lesions of already dead branches there were orange filamentous structures, namely the conidial horns of the pathogen. Some lesions had small black tumor-like granules beneath the bark, namely the fungus stromata. Further indoor examination and consultation of relevant literature confirmed that this was chestnut blight, and the pathogen was the chestnut blight fungus, belonging to Ascomycetes, Diaporthales, Valsaceae, Endothia.
I. Occurrence Pattern and Symptoms
The pathogen is a facultative parasite, overwintering in diseased tissues as mycelial layers, perithecia, and pycnidia. Both conidia and ascospores can cause infection. Each December, ascospores gradually mature and spread outward via human activity, insects, birds, wind, or rain, invading new host wounds. From late March to April of the following year, when the temperature reaches above 4-5 degrees C, the pathogen begins to grow and the host begins to develop disease. Because the temperature is low at this time, lesions develop slowly; when the temperature rises to 20-30 degrees C, lesions expand more rapidly and disease severity increases. Beneath the bark of lesions, small black tumor-like granules are produced, which are the fungal stromata. Shortly afterward, the tops of the stromata break through the bark, and during rainy weather, orange-yellow tendril-like conidial horns are squeezed out from within the stromata. Cylindrical, single-celled conidia are released and enter the cycle of asexual reproduction and infection. Finally, the stromata turn orange-red to dark red, and within them gradually form flask-shaped, black perithecia that are darker in the upper part and lighter in the lower part, producing club-shaped asci and releasing ascospores. Between the diseased bark and xylem, feather-like fan-shaped mycelial layers can be seen, dirty white-yellow or yellow-brown in color. When the temperature drops below 10 degrees C, lesion development slows and eventually stops, entering the overwintering period.
II. Control Measures
1. Comprehensively remove dead plants and branches and trunks. Dig out dead plants including the roots, apply quicklime in the holes for disinfection, and prune out dead branches as well as branches with relatively large lesions on some branches and trunks and some weak branches with poor growth.
2. For smaller lesions on relatively thick branches and trunks, scrape them off with a knife, and apply 0.5 degree Baume lime-sulfur mixture to the scraped areas, the wounds from pruned branches, and other wounds with mechanical damage.
3. Immediately spray comprehensively with 500-fold dexon solution, once every 15 days, for 3 consecutive sprays. Observation after application showed that dexon had a clear therapeutic effect on chestnut blight. In the treated chestnut forest, no plants were found to have died from chestnut blight, branches and trunks infected by the disease were extremely rare, and the entire chestnut forest grew vigorously. In contrast, in the untreated chestnut forest, the plant mortality rate reached as high as 20%, and lesions ranging from 1-2 cm in size were found on the plants, with the overall health of the chestnut trees also being poor.
4. Throughout the entire growth period of chestnut, once pests are found damaging tender shoots or leaves, immediately apply 1:1500-fold dimethoate or decis to control them, protecting leaves and branches from damage.
5. In early spring, loosen the soil once. Turn the soil from the base of the trunk outward, from shallow to deep, taking care not to damage the chestnut tree roots. In conjunction with turning the soil, apply 250-500 kg of urea or compound fertilizer per tree, or 1-1.5 kg of cake fertilizer, or 2.5-3.5 kg of farmyard manure, plus 50 g of carbofuran, to promote root growth and nutrient supply to the trees, strengthen tree vigor, and at the same time kill soil pests such as white grubs.
6. Strengthen tending and management, weed promptly, eliminate weed overgrowth, practice intercropping of trees and crops, drain and irrigate promptly, and apply a topdressing of quick-acting nitrogen fertilizer at 250 g per tree in mid-June. Prohibit people and livestock from entering the forest and causing damage.
7. Eliminate other infected Fagaceae trees near the chestnut forest to reduce future sources of infection.
8. Strengthen quarantine work, select superior and disease-resistant varieties to renovate the chestnut forest, and soak introduced branches and plants in 180-fold lime double-strength Bordeaux mixture before use.
9. Before winter, loosen the soil once in young forests, apply 1.5-2.5 kg of farmyard manure or 1-1.5 kg of cake fertilizer per tree to improve soil structure, increase soil fertility and organic matter content, provide sufficient nutrients for chestnut growth the following year, and mound soil around the tree roots into a conical shape, then uncover it in early spring, reducing the chance of frost damage in young forests. At the same time, spray once with 200-fold lime double-strength Bordeaux mixture to protect the trees through winter.
10. In early spring before chestnut budbreak, spray once with 2-3 degree Baume lime-sulfur mixture; after budbreak, spray again with 0.5 degree Baume lime-sulfur mixture to protect wounds from infection and reduce the probability of disease occurrence.