Botrytis gray mold is one of the important diseases of tomatoes grown in greenhouses during winter and spring and overwintering. There have been many cases recently. It mainly damages young flowers, fruits and leaves. On leaves infected with gray mold, the fungus first infects from the edges of the leaves, showing typical V-shaped lesions. The pathogen infects from the flowering stage, and the pathogen remains on the stigma, and then spreads to the green fruit, fruit surface, and fruit stem, causing the infected green fruit to turn gray-white, soft and rotten, and grow a large amount of gray-green mold layer.
Botrytis cinerea overwinters and summers on diseased remains as sclerotia, mycelium, and conidia. Pathogenic bacteria are weakly parasitic bacteria and invade from wounds, aging organs and flower organs. The petals and stigmas of tomatoes that are not easy to fall off after being dipped in flowers are susceptible parts, causing the fruit to become susceptible to disease and soft rot.
The flowering period is the peak period for gray mold infection. Re-infection is carried out through air current propagation and agricultural operation belts. The suitable temperature for the onset of disease is 200-23 degrees, and the humidity is above 90%. Low temperature, high humidity, and low light are conducive to the onset of the disease. Flood irrigation, continuous cloudy or hazy weather, and foggy days are important factors that induce gray mold. Excessive density, lack of timely ventilation, excessive nitrogen fertilizer, calcium deficiency in alkaline soil, and weakened growth are all conducive to the occurrence and spread of gray mold.
Farmers often complain that once gray mold occurs, even if they use all available fungicides, even special fungicides specifically designed to prevent and control gray mold, they will not work.
Why is gray mold difficult to treat?
The gray mold pathogen reproduces very quickly, with an alarming number of spores and a very high reproduction rate. The English name of the gray mold pathogen is "botrytis", which means "grape ear". The conidia (those gray-brown mold-like things on the infected parts) look like grape ears under a microscope, and the number is astonishing. Use a needle to pick up a little gray mold-like substance on the diseased fruit and put it under a microscope. The number of conidia is countless.
The pathogen has strong survivability: Botrytis cinerea has strong adaptability and survivability. It can absorb nutrients from living plant tissues and survive in dead remains. It is a semi-biotrophic pathogen. Taking cucumber gray mold as an example, the conidia of the pathogen can survive on susceptible fruits, petals, calyxes, stems, and leaves for 4 to 6 months, and the sclerotia can survive longer. Botrytis cinerea can live and inhabit in the soil, on plants, on the back walls of greenhouses, on pillars, and on hanging wires, and can be spread to plants through airflow, rain, farm work, etc. Once conditions are right, the infection germinates quickly.
Bacteria are easy to invade from wounds: Botrytis cinerea prefers "sweet and tender" fruits, and its favorite parts to infect are flowers, young fruits and fruits at the ripening stage of color change. The reason is that some secretions on the flower organs will stimulate the rapid reproduction of pathogens. Once there are wounds on the young skin or mature white fruits, the pathogens will "follow" the juice oozing out of these parts and enter. A survey found that tomato gray mold pathogen has the highest probability of invading fruits from the remaining petals, accounting for 86.27% to 91.61% of all invasions. After dipping the flowers with a regulator during production, the petal residue rate on the fruit pedicle was 67.71% to 100%. This is also one of the reasons why the incidence of gray mold in greenhouse tomatoes is high.
High humidity makes gray mold prone to outbreaks: Weather is an important factor affecting the rate of gray mold occurrence. Botrytis cinerea prefers relatively cool temperatures (18~23℃), high humidity (above 85%), and weather with insufficient light. Therefore, when there are continuous cloudy days with snow or rain, gray mold can easily break out. The pathogenicity of the pathogen is strong: the rapid expansion of Botrytis cinerea has a strong pathogenicity. Once it invades a plant organ, it will quickly show symptoms and produce new conidia quickly. Therefore, once the disease occurs, it means that the number of bacterial pathogens can easily expand explosively, and an epidemic will occur if there is a slight delay.
How to treat gray mold?
Physical prevention and control: In early spring, change the wind release in the morning to the short-term release of moisture in the early morning. Release the fog in the shed as early as possible in the early morning. The method is: Open the air vents of the greenhouse film as wide as possible and keep people away. Wait for the fog in the shed to clear and replace the humidity as soon as possible. After the air transparency increases, quickly close the air vents to speed up the temperature increase and benefit the growth of tomatoes.
Clean up diseased remains and remove diseased fruits, leaves and side branches in a timely manner. Be careful not to pruning or pruning in rainy weather. Remove concentrated burned and deeply buried diseased branches and vines. Reasonable dense planting, high ridge cultivation and humidity control are the keys. Apply nitrogen, phosphorus and potassium in a balanced manner, and pay attention to disinfection and chemical treatment on the seedbed when raising seedlings.
Chemical treatment: Because tomato gray mold is an infection during the flowering period, the preventive role of chemicals when tomatoes are dipped in flowers is very important. The dispensing method is: Add 10 ml of fludioxonil suspension for every 1500 to 2000 ml of the prepared flower dipping solution such as 65% methylthioethylethiocarb or 2,4-D flower dipping solution, or 2~3 grams of 50% boscalid water-dispersible granules, or 1 gram of 50% fludioxonil wettable powder, etc., can be dipped or applied on the flower to make the flower evenly coated. Three-irrigation and two-spraying method: After transplanting the seedlings in the field, start spraying 7 to 10 days later.
Step 1: Spray 75% chlorothalonil wettable powder once, mix 100 grams of medicine per bag with 3 buckets of water (15 liters per bucket, the same below), once every 7 to 10 days. It can comprehensively prevent various diseases in the seedling stage. Chlorothalonil is mild, does not damage flowers, and is not prone to phytotoxicity.
Step 2 (tomato seedlings ~ early flowering stage): root irrigation with 25% azoxystrobin suspension, 5 barrels of water per 50 ml azoxystrobin/acre, 20 days/time. It can comprehensively prevent and control tomato leaf mold, gray mold, and early and late blight.
Step 3: Spray 50% fludioxonil wettable powder 3000 times once, mix 3 grams per bag with 1 bucket of water, once every 14 days. To focus on preventing and controlling the occurrence of gray mold on tomatoes, it is necessary to kill the gray mold bacteria on young tomato fruits. Young fruits must be sprayed with fludioxonil 3000 times or pyrimethanil 1200 times to ensure the best control effect. (The young fruit stage of the first ear of tomato and the flowering stage of the second ear)
Step 4: Spray 25% azoxystrobin suspension + 47% kasurabolin wettable powder once, and mix 1 bucket of water for every 10 ml of azoxystrobin + 30 g kasurabolone, once every 15 to 20 days. Focus on preventing and controlling the occurrence of canker, gray mold and late blight diseases at the early fruit ear stage of tomatoes. (Tomato first ear young fruit expansion stage, second ear young fruit stage, third ear flowering stage)
Step 5: Root irrigation, 120 ml/acre of 25% azoxystrobin suspension at a time, 100 ml of medicine per bottle and 150 liters of water for root irrigation, once every 20 to 30 days. The focus is to strengthen immune prevention, strengthen the seedlings, maintain the fruiting period, and protect the seedlings and fruits. (The first young fruit of the tomato ear has just begun to grow, the second and third young fruits are in the enlarging stage and the fourth ear is blooming.) (In the fruiting stage, the tomato plant, leaves and fruits are basically grown, and the basic structure for a good harvest and production is established. )
Step 6: Spray 32.5% pyraclostrobin * azoxystrobin suspension 1500 times solution 10 to 14 days / once. Systemic fungicides are mainly used to prevent and control tomato leaf mold and gray leaf spot, various diseases that are prone to occur due to large temperature differences in greenhouses.
