Why Gray Mold Is Hard to Control and How to Prevent and Treat It

Frequent continuous rainfall and relatively low temperatures inside greenhouses create favorable conditions for the occurrence and spread of gray mold. Grape gray mold, cucumber gray mold, tomato gray mold, strawberry gray mold, eggplant gray mold, Chinese chive gray mold, and so on - no matter which one, all are extremely difficult to control. Farmers often complain that once gray mold breaks out, even using every fungicide they can buy, including specialized fungicides specifically for controlling gray mold, nothing works. Why is gray mold so hard to control? How do you prevent and treat gray mold?

1. Why is gray mold so hard to control?

1. The pathogen reproduces very quickly

The pathogen reproduces quickly and its spore count is astonishing. The reproduction rate of the gray mold pathogen is extremely high. The English name of the gray mold pathogen is “botrytis”, meaning “grape cluster”. Its conidia (the grayish-brown moldy substances on infected parts), under a microscope, look just like grape clusters, and their numbers are astonishing.

2. The pathogen has very strong survival ability

The gray mold pathogen has very strong adaptability and survival ability. It can take nutrients from living plant tissues and can also survive in dead residues, belonging to the hemibiotrophic type of pathogen. Taking cucumber gray mold as an example, the pathogen's conidia can survive for 4~6 months on infected fruits, petals, calyxes, stems, and leaves, and the sclerotia survive even longer. The gray mold pathogen can survive and inhabit the soil, plants, the back wall of the greenhouse, pillars, and hanging wires, and spread to plants through airflow, rainwater, farming operations, and other routes. Once conditions are suitable, it rapidly germinates and infects.

3. The pathogen easily invades through wounds

The gray mold pathogen likes things that are “sweet and tender”, and its favorite infection sites are flowers, young fruits, and fruits at the color-changing ripening stage. The reason is that some secretions on the floral organs stimulate the pathogen to reproduce rapidly, and once a wound appears on the tender epidermis or on a fruit at the ripening stage, the pathogen will “follow” the sap oozing from these sites and take advantage of the opening. Surveys have found that the tomato gray mold pathogen invades fruits from residual petals with the highest probability, accounting for 86.27% ~ 91.61% of all invasions. In production, after dipping flowers with growth regulators, the residual petal rate at the fruit stem is 67.71%~100%. This is also one of the reasons why the incidence of gray mold in greenhouse tomatoes is very high.

2. Under what conditions is gray mold likely to occur?

1. High humidity makes gray mold prone to outbreak

Weather is an important factor affecting the rate at which gray mold occurs. The gray mold pathogen prefers relatively cool temperatures (18~23°C) and very high humidity (above 85%), as well as weather with insufficient light. Therefore, in weather with continuous overcast days, snow, or rain, gray mold easily breaks out.

2. The pathogen is highly virulent

Amplifies rapidly. The gray mold pathogen has extremely strong pathogenic ability. Once it invades plant organs, it quickly shows symptoms and rapidly produces new conidia. Therefore, once the disease occurs, it means the number of inoculum sources can easily expand explosively, and with the slightest delay it will break out and spread.

3. How to prevent and treat gray mold?

1. For gray mold, prevention is more important than treatment

For the reasons above, once gray mold occurs, spraying chemicals for control is often already too late. Therefore, gray mold should focus on prevention.

2. Reduce the pathogen base of gray mold

The gray mold pathogen inhabits and moves about in the soil and in plant residue tissues. Therefore, before planting vegetables or fruit trees or in the early planting period, and before and after flowering, especially after flower dipping, pay attention to clearing away these diseased branches, leaves, flowers, and fruits, and then use fungicides such as fludioxonil, procymidone, and iprodione to comprehensively treat the soil, floral organs, young fruits, and the entire greenhouse. This can greatly reduce the number of gray mold pathogens.

3. Apply medication early for control

When the gray mold pathogen infects a plant, it first comes into contact with the plant body. Near stomata, lenticels, or wounds, the conidia germinate into germ tubes and appressoria. The appressoria secrete cutinase, lipase, and other lytic enzymes to pass through the cuticle, destroy the epidermal layer, and form an infection burst point on the plant surface. They secrete cell wall-degrading enzymes such as endopolygalacturonase, pectin methylesterase, cellulase, and hemicellulase, decomposing plant organs to help the hyphae absorb nutrients from them.