Symptoms, Identification and Control Methods of Lettuce Gray Mold
Gray mold is a common disease during lettuce cultivation. Once it occurs, it has a great impact on growers, affecting not only quality but also yield. So what are the symptoms of lettuce gray mold? How to control it?
1. What are the symptoms of lettuce gray mold?
Lettuce gray mold mainly harms the leaves, generally starting from the leaves near the ground. At first, they appear water-soaked with irregular lesions, which later expand and turn brown, forming irregular lesions of varying shape and size. In humid environments, a gray or grayish-white mold layer grows on the diseased parts.
The gray mold pathogen can survive and inhabit the soil, on plants, on the back wall of the greenhouse, on the pillars, and on the hanging wires. It spreads to plants through airflow, rainwater, farming operations and other channels, and once conditions are suitable, it rapidly germinates and infects.
The pathogen easily invades through wounds. The gray mold pathogen likes “sweet and tender” parts, and its favorite infection sites are flowers, young fruit and fruit at the color-turning ripening stage. The reason is that some secretions on the flower organs stimulate the rapid reproduction of the pathogen, and once a wound appears on the young epidermis or on fruit at the mature stage, the pathogen will “follow” the juice oozing from these parts and take advantage of the opening to invade.
Gray mold is prone to outbreak when humidity is high. Weather is an important reason affecting the rate at which gray mold occurs. The gray mold pathogen likes relatively cool temperatures (18~23°C) and very high humidity (above 85%), as well as weather with insufficient light. Therefore, in continuous cloudy, snowy or rainy weather, gray mold is very likely to break out.
2. How to control lettuce gray mold?
1. Agricultural control
Manage water and fertilizer reasonably, strengthen healthy cultivation, and promptly remove accumulated snow on the shed roof and accumulated water outside the shed after rainy and snowy weather.
Use plastic film dark irrigation or drip irrigation, avoid flood irrigation, and ventilate promptly after irrigation to reduce humidity. Prune and remove side branches at the proper time to improve ventilation and light penetration in the lower part of the plants. Promptly remove old lower leaves and diseased flowers, diseased fruit and diseased branches and leaves, take them out of the shed and compost them in a centralized pile or bury them deeply to reduce sources of infection. Regulate the temperature and humidity in the shed well to create environmental conditions unfavorable for the occurrence of gray mold. On sunny winter mornings, ventilate for 30 minutes to reduce humidity below 75%, then close the shed tightly, and after the temperature inside the shed rises to 30°C, ventilate slightly to keep the temperature at 28~32°C; in the afternoon, increase ventilation and keep humidity below 70%.
2. Biological control
Use biological pesticides to control gray mold. At the early stage of gray mold in protected vegetable cultivation, use 125~150 grams of 10% polyoxin wettable powder per mu, or 100~166 grams of 300 million CFU/g Trichoderma harzianum wettable powder, or 45~55 grams of 100 billion spores/g Bacillus subtilis wettable powder, or 125~250 grams of 200 million/g Trichoderma wettable powder, or 100~120 milliliters of 1% phenazine-1-carboxylic acid suspension concentrate, add 20~30 kilograms of water and spray evenly.
3. Chemical control
(1) Smoke method. At the early stage of disease, use 175~200 grams of 20% procymidone · chlorothalonil smoke agent per mu, or 250~300 grams of 15% iprodione · chlorothalonil smoke agent, place them in 4-5 spots inside the shed, light them in the evening, ventilate the next morning, and fumigate again after 7~10 days.
(2) Spray method. At the early stage of disease, use 60~80 grams of 25% procymidone · thiram wettable powder per mu, or 75~100 milliliters of 50% procymidone suspension concentrate, or 50~100 milliliters of 50% iprodione suspension concentrate, or 26~36 milliliters of 22.5% picoxystrobin suspension concentrate, or 125~180 milliliters of 20% pyrimethanil suspension concentrate, or 67~83 milliliters of 30% boscalid suspension concentrate, or 40~60 milliliters of 30% pyrimethanil · tebuconazole suspension concentrate, or 30~45 milliliters of 43% fluopicolide · trifloxystrobin suspension concentrate, or 9~12 milliliters of 30% fludioxonil suspension concentrate, or 45~60 milliliters of 30% boscalid · fludioxonil suspension concentrate, or 27~35 grams of 50% fluazinam water-dispersible granules, or 155~190 grams of 50% captan wettable powder, add 20~30 kilograms of water and spray evenly. Do not spray with a large amount of water, and ventilate promptly after application to reduce humidity, so as to prevent increasing the humidity inside the shed and promoting disease occurrence. Pay attention to safe pesticide use, and insist on rotating and alternating pesticides. Harvest after the pesticide safety interval to ensure that pesticide residues do not exceed the standard.