How to prevent and control grape black pox disease? Key points for disease prevention when growing grapes

Grape black pox disease is also known as scab and bird's eye disease. Common names include toad's eye, liulong, and black spot. This disease is an important disease of grapes. It generally begins to occur in mid-to-late April, with the peak period from mid-to-late May to early June, and it is severe in rainy seasons. It occurs throughout Shanxi Province, and is more severe in rainy years, in orchards with poor drainage, under extensive management, and on weakened trees.

Symptoms: The young and tender parts of grape leaves, rachis, fruit stalks, tendrils, new shoots, and fruit can all be affected. Affected parts produce brown spots; leaves, young shoots, and tendrils become twisted and shrunken, and young fruit becomes deformed. 1. Young leaves: The disease occurs at the leaf expansion stage. After infection, spots appear on the leaves, initially round and light reddish-brown, then gradually expanding and becoming nearly circular; the center of the spot turns gray, the edge is dark brown, and the mesophyll in the center of the spot easily dies, forming shot holes. After the main vein of young leaves is affected, the leaves become deformed and shrink and curl. Spots on young fruit are round, initially brown, then expand and become slightly sunken, with a gray conidial acervulus in the center, surrounded by dark brown and encircled by a reddish-purple ring, resembling a bird's eye. 2. New shoots: The spots are long oval, with edges fading from purple to black, slightly raised, and the center gray and sunken, sometimes reaching deep into the xylem or pith, with cracking. New shoots begin to develop the disease from the tip and gradually spread downward. In severe cases, the entire new shoot turns black and dies. After young shoots, petioles, and fruit stalks are damaged, purple-brown long oval spots first appear, then turn black and sunken; in severe cases, the spots connect and the diseased shoot dries up. This disease generally begins to occur in mid-to-late April, with the peak period from mid-to-late May to early June, and it is severe in rainy seasons. 3. Inflorescences: After infection, light brown spots first appear, then turn black; in severe cases, the entire inflorescence or flower buds dry up or drop. 4. Rachis: The disease causes poor development or even death of the whole cluster or some spikelets. Affected fruit stalks can cause fruit to dry up and drop or become mummified. 5. Young fruit: After infection, small brown round spots first appear on the fruit surface, then expand, with the center grayish-white and sunken, bearing small black granules. Affected young fruit often stops growing and easily drops. If the fruit is larger when affected, it turns dark green, grows slowly or becomes deformed, hard in texture, and sour in taste; sometimes it splits from the diseased part, exposing the seeds; sometimes even if it can ripen, it often changes flavor and later rots. Pathogen: Belongs to the fungal kingdom, Ascomycota. Sphaceloma; the sexual stage has not yet been found in China. The conidial acervulus is semi-embedded in the host tissue; the conidiophores are short and small, colorless, single-celled, measuring 6.6-13.2×1.3-2μm. Conidia are oval or round, colorless, single-celled, slightly curved, each end with 1 oil droplet, measuring 4.8-11.6×2.2-3.7μm. The ascocarp is initially embedded in the diseased tissue, then breaks through the epidermis and becomes exposed; the whole is a block-shaped irregular stroma composed of pseudoparenchyma, with a crust-like outer layer, containing multiple irregularly arranged cavities, each cavity bearing 1 ascus. Asci are colorless, nearly spherical, containing 4-8 ascospores. Ascospores are colorless, banana-shaped, with 3 septa, measuring 15-16×4-4.5μm. The pathogen's development temperature is 10-40°C, with the optimum temperature at 30°C; conidia are easily formed at 24-25°C and high humidity. Conidia can germinate between 10-40°C, with the suitable temperature at 24-25°C; above 30°C, budding spores are often produced. Infection cycle: The pathogen mainly overwinters as mycelium latent in tissues such as diseased canes and diseased shoots, and can also overwinter in diseased fruit, diseased leaves, and leaf scars. The pathogen has strong vitality and can survive in diseased tissues for as long as 3-5 years. In April-May of the following year, new conidia are produced and spread by wind and rain. After the spores germinate, the germ tube directly invades the host, causing primary infection. After invasion, the mycelium mainly spreads beneath the epidermis. Later, conidial acervuli form in the diseased parts, break through the epidermis, and under high humidity conditions continuously produce conidia for repeated infection. Short-distance spread of the pathogen mainly relies on rainwater, while long-distance spread relies on diseased canes. The formation of conidia requires a temperature of about 25°C and relatively high humidity. The mycelial growth temperature range is 10-40°C, with the optimum at 30°C; the incubation period is generally 6-12 days, shortest at 24-30°C, and disease development is inhibited above 30°C. New shoots and young leaves are most susceptible, and their incubation period is also shorter. The bleeding of black pox disease is closely related to rainfall, atmospheric humidity, and the tenderness of the plant, especially to the amount of rain in spring and early summer from April to June. Rainy and humid conditions favor the formation, spread, and germinating invasion of conidia; at the same time, rainy and humid conditions also cause rapid growth of host tissues, so the disease occurs severely. In dry years or areas with little rain, the disease is significantly reduced. Black pox disease can continuously cause damage from May to October, and after the rainy season arrives in July it enters the peak period. The disease first occurs on young shoots and young leaves just emerging from the buds, that is, it begins at the leaf expansion stage, and after flowering it successively attacks fruit clusters and berries. Conditions for disease occurrence 1. Rainy and high humidity are the dominant factors in the occurrence and epidemic of the disease; even 1-2 small rainfall events can promote the development of the disease. Conversely, under drought conditions the disease is significantly reduced. Experiments have shown that under dry conditions, no spores can be produced on diseased parts on the ground or on the tree. Shanxi Province has drought in nine out of ten years, especially severe in the central and northern regions, so in ordinary years black pox disease occurs only mildly. 2. Orchards in low-lying areas with poor drainage often have more severe disease. Poor cultivation management, weakened tree vigor, insufficient fertilizer or improper combinations, etc., can all induce disease occurrence. In particular, failure to pay attention to orchard sanitation in winter, with large amounts of diseased residues left in the orchard, creates conditions for the pathogen to overwinter and spread the following year. 3. Grapes differ in disease resistance at different growth stages. Generally, as the maturity of tissues in each part increases, disease resistance also strengthens. Leaves that have stopped growing are almost not infected. After the fruit colors, resistance gradually strengthens. When the cane epidermis becomes colored, it is basically not affected. 4. Disease resistance varies greatly among varieties. In terms of variety susceptibility: Eastern varieties and local varieties are susceptible, and individual Western European varieties are also susceptible, but the vast majority of Western European varieties and Black Sea varieties are resistant, and European-American hybrids are rarely susceptible. Among severely susceptible varieties are Jimiyate, Yangnai, Longyan, Thompson Seedless, and Baoregare; moderately susceptible varieties include Queen of the Vineyard, Muscat Hamburg, New Rose, Italia, and Xiaohong Rose; slightly susceptible varieties include Pearl of Csaba, Superior Muscat Hamburg, Frankenthal, Garrigues, and Gimus; resistant varieties include Taso, Youxiangjiao, Bahe, Seibel 2003, Seibel 2007, Crystal, Golden Queen, and Black Tiger Fragrance.  Control methods 1. Breed resistant varieties There are great differences in disease resistance among grape varieties, so varieties with good horticultural traits and disease resistance can be selected for cultivation. 2. Eliminate the pathogen source Combined with summer pruning, thoroughly remove diseased shoots and diseased fruit and remove diseased leaves; after winter pruning, clear fallen branches and leaves and burn them centrally to reduce the pathogen source and lessen the disease. 3. Strengthen plant management Prevent excessive application of nitrogen fertilizer, reasonably increase the application of phosphorus and potassium fertilizers, strengthen tree vigor, prevent excessive vine growth, and improve resistance; reasonably adjust the canopy branches and vines so that they are evenly distributed and form a tree structure with good ventilation and light penetration. 4. Disinfection of nursery stock and cuttings Newly built vineyards must disinfect the nursery stock used and the cuttings used in nursery plots before planting and cutting. Commonly used disinfectants include: 10-15% ammonium sulfate solution and ferrous sulfate-sulfuric acid mixture (% ferrous sulfate + 1% crude sulfuric acid), 3-5% copper sulfate solution, and 3-5 degrees Baume lime sulfur mixture, etc. The method is: soak the nursery stock or cuttings in any one of the above liquids for 3-5 minutes, then remove and rinse with clean water. 5. Chemical control a. Carry out control from grape leaf expansion to before fruit coloring, spraying once every 10-15 d; before flowering and when 70%-80% of flowers have fallen, spray 2 times consecutively. Chemicals that can be used include 0.5% half-strength lime Bordeaux mixture, 50% carbendazim wettable powder 800-fold solution, Daconil M-45, 800-1000-fold solution, 80% Pencozeb wettable powder 800-fold solution, and 5% junjimei aqueous solution 1000-fold solution. b. After leaf fall and before bud break, use 3-5 degrees Baume lime sulfur mixture + 0.2-0.3% sodium pentachlorophenate (PCP) to eliminate overwintering pathogen sources; during the growing season, spray once each before and after flowering with 1:0.5:200-240 Bordeaux mixture, then spray 200-fold equal-strength Bordeaux mixture once every half month. In the later growth stage, 50% Tuzet 800-1000-fold solution or 50% carbendazim 1000-fold solution can be used, which can also control other diseases.