Symptoms (Figure 2-57)
Fig. 2-57 Freckle disease of olive hole
1. diseased leaves (leaf surface and leaf back) 2. Consequence 3 Conidiophore and germinated conidia.
The disease is mainly caused by the formation of annular lesions on the leaves, and the spots on the back of the leaves are not obvious. At first, the lesion was a small gray-black spot with brown surrounding, and then it gradually expanded, and the surrounding color changed from light brown to dark brown. The diameter of the large lesion can reach10-12 mm. In warm months, there is a yellow circle around the lesion, which looks like peacock's eyes, hence the name hole freckle. In severe cases, there are many diseased spots on a leaf, and the diseased leaves gradually turn yellow and fall off early. Fruit is susceptible to disease when it is ripe, and the surface of diseased fruit appears round brown spot and slightly concave, and its symptoms are the same as those on leaves. The diseased spots on the branches are small, the symptoms are not obvious, and it is not easy to detect.
cause of a disease
This disease is a kind of semi-unknown bacteria, and sexual reproduction has not been found yet. Pathogens propagate by conidia and spread by wind. When conidia fall on the surface of leaves, they germinate, grow hyphae, invade the epidermis of leaves, gradually extend and absorb nutrients, causing local tissue necrosis and forming lesions. The mycelium is brown and develops to a certain extent, and many short branches are formed on it, which extend out of the leaf surface and become spore stalks. Conidia are produced at the top of spore stalk. With a magnifying glass, we can see that there is a layer of dark brown mold on the surface of the lesion. Microscopically, it can be seen that conidia are nearly oval, with one end large and the other small. Most of them are single cells, and a few are brown, with the size of14-27×10-12 μ m.
Occurrence law
This pathogen overwinters with mycelium and conidia. Mycelia buried in leaf tissue keeps vitality all the year round. The production, reproduction and germination of conidia need suitable environmental conditions. The incubation period of this disease is usually two weeks, sometimes as long as several months. Therefore, the occurrence, development and harm degree of the disease largely depend on the influence of external environmental conditions. In the dry season, when the temperature is higher or lower, the pathogen stops reproducing; When rainfall or atmospheric relative humidity is high, it can promote the growth and reproduction of pathogenic bacteria. When the humidity is appropriate and the temperature is not lower than 3-5℃, pathogenic bacteria can also grow and reproduce. In Kunming, Haikou, Hainan and other places in Yunnan, the rainy season comes every year, and the disease gradually develops and spreads rapidly from July to August. September-165438+1October With the decrease of rain and the arrival of dry season, diseased leaves fall off earlier, and when the disease is serious, it often causes a lot of fallen leaves. When more nitrogen fertilizer is applied, the conditions of fertilizer and water are better, and the branches and leaves grow too densely, the harm of hole spots is serious.
There are also differences in disease resistance of varieties. Frantoio is more resistant to diseases, followed by Berat and Elbesan. Calino is ill.
Prevention and cure method
1. Enhance disease resistance
Timely irrigation, rational fertilization, moderate pruning, enhance tree vigor and improve plant disease resistance.
2. Eliminate overwintering pathogens
Combined with management, the fallen leaves and fruits on the ground are removed, and the overwintering bacteria are eliminated.
3. Chemical control
After the rainy season comes, spray 1.5% bordeaux mixture or 0.4% zineb (65% wettable powder) 2-3 times (spray every 15-20 days/time). Spraying medicine after rain is better. In case of heavy rain after spraying, it must be sprayed again. It is best to spray Bordeaux mixture in areas with frequent rain.