How to identify and control purple blotch of onion?
What is purple blotch of onion? How to control it? Please guide on purple blotch of onion: 1. Symptoms Purple blotch mainly affects onions and Welsh onions, and also infects and damages garlic and Chinese chives. On onions it mainly damages leaves, flower stalks and bulbs. The lesions first appear starting from the leaf tip, or form at wounds caused by thrips. Initially...
What is purple blotch of onion? How to control it? Please guide
Purple blotch of onion:
1. Symptoms
Purple blotch mainly affects onions and Welsh onions, and also infects and damages garlic and Chinese chives. On onions it mainly damages leaves, flower stalks and bulbs. The lesions first appear starting from the leaf tip, or form at wounds caused by thrips. In the early stage the lesions are small, gray to light brown, slightly purple in the center, with dark gray mold-like growth. The lesions quickly enlarge into an oval or spindle shape, sunken, dark purple, forming concentric rings, surrounded by a yellow halo. When humidity is high, the lesions expand to cover the whole leaf, often causing the onion leaves to turn yellow, die or break from the bottom upward, seriously affecting the yield and quality of fresh onions.
2. Control methods
1. Clean the field and remove sources of infection such as diseased plant residues.
2. Strengthen management, apply more base fertilizer and topdressing to make onions grow vigorously and enhance disease resistance. After the disease occurs, control irrigation to reduce soil moisture, and control thrips early to avoid causing wounds.
3. Chemical control: Soak seeds in a 300-fold dilution of 40% formaldehyde for 3 hours, then wash them promptly. In the early stage of the disease, spray 75% chlorothalonil wettable powder 600-fold dilution, 64% Sandofan wettable powder 500-fold dilution, 80% Lvheng mancozeb 500-fold dilution, 40% Dafudan 500-fold dilution, 50% iprodione 1500-fold dilution, 2% polyoxin 30ppm, 50% procymidone 30-50 grams, onion and garlic disease cleaner and other agents. Any one of the above agents may be chosen, and the various agents should be used alternately, once every 7-10 days, for 3 consecutive treatments. Adding 5-10 grams of neutral laundry detergent to every 10 kg of spray solution can increase the adhesion of the solution.
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