Prevention and treatment of canker of grapefruit

Symptom characteristics

Damage leaves, shoots and fruits. What the symptoms have in common is that the disease spot with cork uplift appears in all the affected parts, and the middle part of the spot is cracked in the shape of "crater"; the difference is that the leaf cork spot penetrates the front and back of the leaf, the yellow halo appears around the spot, and the yellow halo around the fruit branch spot is not or not obvious.

Pathogen and characteristics of disease

The pathogen is a kind of bacteria. It is said that the pathogen of grapefruit is mainly latent in leaves, branches and fruit diseased tissues, especially the disease spot on autumn shoot is the main overwintering place, which becomes the main primary infection source of the disease in the following year. In the next spring, when the temperature and water humidity are suitable, the bacteria overflow from the disease spot, spread through wind and rain, insects, branch and leaf contact and agricultural operation, and invade from stomata, lenticels and wounds to cause disease. Long-distance transmission is through the transport of infected seedlings, scions and fruits. The incidence of disease was favorable in years and seasons with high temperature and heavy rain, especially in years and seasons with frequent typhoons and torrential rains. Under the condition of suitable temperature (25: 30 ℃), rain days and rainfall were positively correlated with the disease, and the orchards with partial application of nitrogen fertilizer, rampant leaf miner, poor control of summer shoots, irregular autumn shoots and mixed planting of varieties were more serious, and the disease of seedlings and young trees was more serious than that of old trees. Sweet oranges are the most susceptible, grapefruit and lemon take the second place, oranges are more resistant, and kumquat are the most resistant; the pathogen only infects the young tissues at a certain stage of development (stomata have been formed).

Prevention and cure method

(1) strict seedling quarantine and cultivation of disease-free seedlings. Seedlings and scions imported from other places should be soaked with 700 units / ml of streptomycin + 1% alcohol for 60 minutes, or with 0.12 litres of mercury or 0.3% ferrous sulfate for 10 minutes. The disease-free nursery should be 3 kilometers away from the citrus garden. (2) pruning the garden with the combination of winter and spring, thoroughly clearing the garden, and then spraying the ground and trees for once (30% copper oxychloride or 800-1000 times of "backing" suspension). (3) do a good job of wiping buds and controlling shoots to reduce the incidence of the disease. Young trees control shoots by wiping buds to make summer and autumn shoots spit neatly, in order to protect shoots by spraying, and young and middle-aged trees control summer shoots by wiping buds to reduce disease. (4) rational fertilization, controlling shoots with fertilizer, controlling leaf moths, butterflies and other pests, mastering leaf moths releasing autumn shoots in low bee period, and building protective forests around gardens in areas with frequent typhoons can reduce the disease. (5) spray spray to protect shoot and fruit. When the length of the new shoot is 1.5 cm to 3 cm, the first spray is applied, and the leaves are sprayed for the second time when the leaves turn green; the adult fruiting trees are mainly to protect the young fruit, and they are sprayed once at 10 days, 30 days and 50 days after flowering. The medicament is made up of 1000 × 1500 times of "backing" suspension, or 77% of chlorpromadil, 30% of copper oxychloride suspension, or 400 × 800 units / ml of agricultural streptomycin + 0.1% alcohol, or 600 times of Chuanhua-018 wettable powder, or 50% plus 800 times of Ruinong wettable powder, or 0.5% of 1% 2flouane 100 times of Bordeaux solution, or 50% of desenamine water agent 500 times of 800 times. You can also try 20% euchlorote soluble powder 400 × 500 times, or 20% quinolone wettable powder 1000 × 1500 times. Note: continuous spraying of Bordeaux liquid is easy to cause rampant mites such as rust ticks, so it should be used in conjunction with acaricides for safety.