Detailed Explanation of Control Methods for the Three Major Diseases of Navel Orange
When navel orange was top-grafted onto mature Satsuma mandarin trees, the fruiting characteristics appeared normal in the first two years, but thereafter varietal degeneration symptoms appeared year by year: shorter shoots, smaller leaves, lighter leaf color, weaker tree vigor; lower fruiting rate, smaller fruit size, dull and lusterless peel, weaker flavor, and declining fruit quality. In production practice...
Fruit cracking, sunscald and navel yellow are the three major physiological diseases of navel orange, and many novice growers lack experience in controlling them. Chen Tangjun is one of the earliest specialized growers of navel orange in Jinhua City, currently growing more than 200 mu of navel orange. Through 15 years of observation and experimentation, he has accumulated rich experience in controlling navel orange fruit cracking, sunscald and navel yellow, and has effectively controlled the occurrence of these diseases. The methods are introduced below for reference by growers in various regions:1. Control of fruit cracking: First, select varieties (lines) with relatively strong cracking resistance; generally, varieties (lines) with oval fruit shape and small or closed navel have better cracking resistance, such as Newhall and others. Second, strengthen scientific management to enhance tree vigor; especially during the drought period from after the plum rain season to before the arrival of autumn rains, water management must be done particularly well, with timely irrigation or watering (sprinkling) to keep the soil moist at all times and promote normal fruit growth and development. Third, during the rapid fruit expansion period, spray foliar potassium fertilizer 2 to 3 times consecutively. For foliar potassium fertilizer, 0.2% monopotassium phosphate or 0.3% potassium sulfate compound fertilizer can be used, and in early to mid-July, apply a mixture of "920" at a concentration of 200 mg/L plus 800-fold thiophanate-methyl and an appropriate amount of fragrant paste, which can heal the cracks and prevent fruit cracking from recurring.
2. Control of sunscald: Strengthen scientific management; covering the orchard with straw and other materials to preserve soil moisture is the foundation for preventing sunscald. Planting forage grass or intercropping green manure in the orchard can reduce sunscald. During hot seasons, do not spray pesticides such as machine oil emulsion or lime sulfur mixture, so as to avoid aggravating the occurrence of sunscald. In the early stage of sunscald, paste white paper onto the surface of sunscalded fruit, and pull branches and leaves to shade the fruit to reduce direct sunlight exposure. During the hot seasons of summer and autumn, regularly irrigate or sprinkle water, which can prevent and reduce the occurrence of sunscald.
3. Control of navel yellow: First, start with cultivating vigorous tree vigor, appropriately increase nitrogen fertilizer application, and raise the tree's nutritional level and nitrogen metabolism function. Second, before flowering, pull strong and vigorous autumn shoots into a drooping or horizontal position so that most flowers face downward when they open, reducing sun-facing fruit and preventing the occurrence of navel yellow. Third, from early to mid-June to mid-to-late July, in combination with fruit retention, spray "920" solution at 30 to 40 mg/L twice consecutively; from late July to late August, use 600-fold "Yellow Inhibitor" solution to coat and spray the navel part of the fruit, so as to suppress the occurrence and spread of navel yellow.