How to prevent and control brown rot in papaya cultivation?
1. Symptoms: Brown rot mainly damages the fruit, but can also damage flowers and young shoots. When the fruit is affected, small brownish, nearly circular spots appear first. As the disease progresses, the spots keep expanding. Under suitable conditions, the spots quickly spread over the entire fruit surface and gradually extend into the flesh. In severe cases, the entire fruit rots. After the diseased fruit loses water, it becomes a brown mummified fruit that hangs on the branch and does not fall for a long time. The pathogen on the pedicel or fruit infects the branches, forming brown canker spots, which affects the normal transport of nutrients and water, inhibits the growth and development of the branches, and causes the branches to die.
2. Disease development pattern: This disease is a fungal disease, and its asexual stage is the genus Monilia in the subphylum Deuteromycotina. The pathogen overwinters on mummified fruit, and the pathogen on diseased branches can also cause infection after overwintering. In the spring of the following year, after the temperature rises, the pathogen on diseased fruit and diseased branches produces conidia, which spread by wind and rain. Around early May, after young fruit forms, the pathogen mostly invades through wounds on the fruit. Therefore, where insect pests are severe and there are many insect wounds, brown rot is also severe. In years with early or abundant rainfall, the disease occurs early and severely; low-lying cultivation sites that are prone to waterlogging and weak tree vigor are also suitable for the disease. During the fruit enlargement stage, if natural disasters such as violent storms and hail occur, many wounds are caused on the fruit surface, which also facilitates pathogen invasion and disease occurrence.
3. Prevention and control methods
1. Handle diseased residues. After the papaya harvest, in combination with winter pruning, cut off diseased branches, remove diseased fruit, and burn them in a centralized manner, which can effectively reduce the overwintering inoculum source.
2. Chemical control. In early spring before papaya sprouts, spray 1 time with 5 degrees Baume lime sulfur mixture; from after papaya flowers fall in March-April to before fruit harvest, every 10-15 days, spray 1 time with 50% carbendazim 500 times or 50% thiophanate-methyl 800 times solution, spraying 2-3 times consecutively, and it can also control leaf diseases.
3. Prevent insect wounds. The peach fruit borer is an important pest damaging papaya fruit. In mid-to-late June, just when papaya fruit is enlarging, the female moth lays eggs in the stem cavity of the fruit and the gaps along the suture. After the larvae hatch, they bite through the fruit skin and bore into the fruit. They not only feed back and forth on the flesh, but also cause insect wounds, which facilitate pathogen invasion. Control method: During the larval hatching period, spray 90% crystal trichlorfon 1000 times solution or fenitrothion emulsifiable concentrate 1500 times solution, once every 7 days, spraying 3 times consecutively.