Symptoms (Figure 2-58)

Figure 2-58 Olive scab

1. Disease Tips 2. Ill leaf 3. Sick fruit 4. Spore 5. acervulus

Scab mainly harms olive fruits and leaves, with obvious symptoms. Generally, there are only 1 brown spots on fruits, and sometimes there are 2-3 brown spots. At first, it was waterlogged brown spot, and it was mostly a wheel spot from the top of the fruit, which gradually expanded. The center of the lesion is slightly concave and slightly hard. When the lesion covers most of the fruit surface, the fruit will shrink and dry, becoming dark brown and hard. In the late stage, there were pale brown granules (acervulus) on the lesion, and a large number of orange-red spore piles were produced under wet conditions. Fruit is most susceptible when it ripens and turns purple. The diseased fruit is easy to fall off, and the susceptible rate of leaves is lower than that of fruits. Young leaves are dark gray when they come up, spread inward from the tip or edge of the leaves, lose the inherent luster of the leaves, curl from the main vein to the leaf surface, become brittle and easy to fall, and the tip of the leaves withers. The diseased part of the old leaves is yellowish brown. The diseased buds are dark gray, easy to atrophy and dry up, and the mortality rate reaches 90% in severe cases. The oil yield of diseased fruit is low, oleic acid is increased, and its utilization value is lost. Orchards with serious diseases lose their ability to bear fruit, and generally reduce production by about 25%.

cause of a disease

The pathogen of the disease is Colletotrichum olivaceum. The sessile fungus is light brown with a single conidia, colorless, spindle-shaped to oblong, with the size of15—24× 4—6 μ m. On potato culture medium, when the temperature is 2 1—23℃, the colony first turns red, and then orange-red spore piles are produced, and the colony turns pink or gray-white, and the surface of the culture medium. The germination rate of conidia was 96.7- 100% after 2 hours on agar medium at 25-28℃.

Occurrence law

Pathogens overwinter on diseased branches and leaves of diseased trees, which is the primary source of infection of diseases in the following year. A large number of new shoots, young leaves and fruits were attacked, which was the result of repeated infection of the disease epidemic in that year. When the temperature is16.1-18.4℃ and the humidity is 84-95%, the incubation period of the pathogen is 4-5 days and the onset period is 5-7 days. Pathogens of various organs and diseases can infect each other. Wounds are more conducive to the invasion of pathogens through the lenticels, stomata and natural orifices of the host. Disease spots appeared after 3 days of abrasion of inoculated fruits.

During the onset period, according to the observation in Chongqing and Luzhou, Sichuan, the onset of new shoots began in early May and peaked from late May to early June, with an incidence rate of 85-92%. The incidence rate decreased from late July to late September. From late September to 10, it entered the second peak. The peak of dead bamboo shoots in the field is from mid-June to early July, and the rate of dead bamboo shoots is about 70%. Dead branches decreased in mid-July, but did not appear in August-September, and the number of dead branches increased to 10 in late September. Fruit disease began in late August and gradually increased from September to June, reaching more than 84%.

Relationship between onset and temperature and humidity. The daily average temperature is 18-25℃, with frequent rainfall. When the relative humidity is 80-90%, the incidence rate is high and the harm is serious. When the daily average temperature is 24-29℃, the disease is suppressed, with little or no disease. Among them, precipitation and humidity are the main factors to promote the occurrence and development of diseases. Rain is the main medium for bacteria to spread. High humidity is beneficial to the generation, germination and invasion of pathogen spores. High temperature and drought have obvious inhibitory effect on the occurrence and spread of diseases.

Pathogens existing in branches and leaves can spread over a long distance through cuttings, scions, seedlings and so on.

The disease resistance of varieties is also different. Bella variety and Su 12 and other big fruit varieties are susceptible to diseases. Foao, Mizha and other small fruit varieties do not get sick or rarely get sick.

Prevention and cure method

1. Strengthen cultivation management, strengthen tree vigor, improve plant disease resistance, combine autumn and winter pruning, completely cut off diseased dead branches, and burn them centrally, so as to reduce the initial infection source of diseases in the next year. Remove the fallen leaves and fruits in the garden in time, and bury or burn them in a centralized way. If necessary, prune them in summer to cut off the source of reinfection.

2. Select disease-resistant varieties to cultivate disease-free seedlings.

3. Pick fruits early to reduce the occurrence of diseased fruits. For large-scale fruit varieties susceptible to diseases such as Bella, harvest them as early as possible according to the use of canned and preserved fruits to reduce and avoid the occurrence of diseased fruits.

4. In the onset period, 0.5% Bordeaux solution was used for chemical control; Qingfengmycin100-150 ppm; Nongkang120 20 ppm; ; Nongkang130 ——10 20 ppm; 500-800 times of 50% thiophanate-methyl wettable powder; 600-800 times of 65% zineb wettable powder; 50% carbendazim WP 1000 times solution. Spray every 15-20 days 1 time, and spray continuously for 2-3 times.