How do you prevent and treat exocortis and root rot in citrus?

China is one of the important places of origin for citrus. Citrus resources are abundant, and there are many excellent varieties. It is also a precious fruit for humans, and in many areas it is cultivated as an economic fruit tree. So how should citrus exocortis and root rot be prevented and treated?

1. How should citrus exocortis and root rot be prevented and treated?

1. Citrus exocortis is one of the important citrus diseases caused by the citrus exocortis viroid. Exocortis can infect many species and varieties of citrus plants, and the symptom reactions vary greatly. Among them, most rootstock varieties such as sour mandarin, red mandarin, sweet orange, sour orange, and rough lemon show no visible symptoms. Citrus plants grafted onto trifoliate orange, citrange, and lemon show obvious symptoms and suffer severe damage. Diseased nursery stock shows no symptoms at the seedling stage, and the time required for bark cracking to appear on field plants is generally 4 to 8 years after planting.

2. Control methods:

(1) Cultivate disease-free nursery stock. Mother trees are identified using the Arizona 861 strain of Etrog citron as an indicator plant, and only those proven disease-free may be used for cutting propagation. Virus-free plants can also be cultivated through shoot-tip grafting for detoxification.

(2) Tools such as grafting knives or pruning shears can be disinfected with 1% sodium hypochlorite solution or a 10-fold dilution of 10% bleaching powder aqueous solution. Soak the tools in the disinfectant or dip a cloth in it and wipe the blade for 1 to 2 seconds, then rinse with clean water, wipe dry, and use.

(3) Implement plant quarantine to prevent spread.

2. How should citrus root rot be prevented and treated?

1. The correct name for citrus root rot is foot rot. It is caused by multiple fungi, with a growth temperature of 10-35 degrees, and this disease easily breaks out at 25-28 degrees. This disease should be prevented primarily in advance, and the selected rootstock should mainly be trifoliate orange and fragrant orange. Sour mandarin (red mandarin) and sour orange have weaker resistance to this disease. When grafting, the graft union should be raised as much as possible, and when planting, it should not be planted too deep; the original soil mark on the nursery stock should be used as the standard. These two methods can greatly reduce the occurrence of this disease.

2. For the prevention and treatment of citrus root rot, comprehensive control measures should be adopted centering on strengthening fertilizer and water management, promoting root growth, and improving root vitality. Specifically, the following links should be well handled:

(1) Improve the drainage and irrigation system of the orchard so as to eliminate the threat of drought and waterlogging and favor root growth.

(2) Apply fully decomposed organic fertilizer, increase the application of phosphorus and potassium, improve the vitality of the plant root system, and promote vigorous growth of the plants and strong tree vigor.

(3) Minimize root damage during intertillage and hilling.

(4) For newly affected plants, the diseased roots may be moderately pruned out (carefully collected and burned) and a Trichoderma harzianum biological preparation may be applied (use according to the instructions), or a 500-fold dilution of tricyclazole suspension concentrate may be drenched (hole irrigation within the canopy area at a certain distance, irrigating thoroughly and sufficiently 2 to 3 times, once every 15 to 20 days). (5) In combination with foliar spraying of leaf nutrient supplements to promote plant growth, hole irrigation on the ground with a 600- to 1000-fold dilution of potassium permanganate can promote root growth. This work should be carried out at least 1 to 2 times per quarter and can be combined with other fertilization management.

Main citrus pests and diseases and their control. During the growth and development of citrus, because the influence of harmful organisms or adverse environmental conditions exceeds its adaptability, its normal growth and development are inhibited, metabolism changes, leading to reduced yield, deteriorated quality, and even death. This brings great losses to the economic value of citrus and seriously affects the economic income of growers. Therefore, clearly understanding the main citrus pests and diseases and taking effective measures for prevention and control is the greatest gain for growers.