Symptom Identification and Control Methods of Lily Gray Mold
Lily, belonging to the genus Lilium in the family Liliaceae, is a perennial herbaceous plant. In recent years, lily cultivation has been severely threatened by diseases, mainly including lily gray mold (leaf blight), Phytophthora blight, basal rot, and viral diseases. These diseases often occur together, compounding the damage. Among them, lily gray mold has the greatest impact on lily growth and cut flower quality, and can even affect the propagation of lily bulbs.
Lily gray mold is a commonly occurring disease. It mainly damages leaves, but can also infect stems and flowers. Infected lily leaves and floral organs frequently develop symptoms such as leaf scorch, deformed flower buds, and wilting petals in the later stages. So how do you identify lily gray mold in actual production?
Scorched appearance when leaves are affected
Early symptoms of the disease
Symptoms of lily gray mold
I. Symptom Identification
1. Stem: After the lily stem is infected by the gray mold pathogen, the affected area turns brown, and the plant easily lodges; after the stem and leaf tips of young plants are infected, the growing point softens and rots, leading to death.
2. Leaves: Early leaf symptoms are transparent water-soaked small spots, which then rapidly expand into brown or reddish-brown circular or oval lesions of varying sizes with water-soaked margins; under low temperature and high humidity conditions, gray or grayish-brown mold-like growth appears on the surface of the lesions, which are the pathogen's conidiophores and conidia; in severe cases, many lesions merge, causing the entire leaf to scorch, resembling "fire damage," and can even cause the whole plant to die.
3. Flowers: Early symptoms on flower buds are small brown spots, which then expand and cause the buds to rot; when the pathogen infects petals, it first produces dotted water-soaked discolored spots, then the lesions expand within a short time and turn light grayish-brown. Mild infection causes only floral deformity, while severe infection causes the entire flower to wilt. Under high humidity conditions, all diseased parts produce large amounts of grayish-brown mold-like growth, all of which are the pathogen's conidia.
II. Pathogen
Generally, gray mold refers to the disease caused by infection with Botrytis cinerea Pers., but the pathogens causing lily gray mold, in addition to
Botrytis cinerea Pers., are mainly Botrytis elliptica (Berk.) Cooke, whose host range is limited to the genus Lilium in the family Liliaceae. B. elliptica is called elliptical Botrytis and belongs to the Deuteromycetes, genus Botrytis.
III. Disease Development Patterns and Transmission Routes
The occurrence of lily gray mold is closely related to climate. The B. elliptica pathogen can survive and grow in soil and on various plant residues, and overwinter in infected host tissues or as sclerotia left in the soil. When temperatures rise in spring, the overwintering mycelium rapidly produces large amounts of conidia, which contact lily leaves or petals via air, rain, and field farming operations; after germination, the mycelial germ tubes can directly penetrate the cuticle to invade lily host cells, or enter through wounds and stomata, completing primary infection; after disease onset, the diseased parts produce conidia for secondary infection. In addition, lily gray mold can also be transmitted via contaminated bulbs, and sites with physiological damage are also prone to gray mold.
The optimum temperature for mycelial growth of the lily gray mold pathogen is 15°C to 25°C, with 20°C being optimal, and relative humidity above 90% favors disease epidemics.
When conditions are suitable, the entire process of spore formation, release, and germination in lily gray mold can be completed in a very short time; consecutive rainy and foggy days, when lily leaves have moisture on them, can lead to outbreaks and epidemics of the disease. For example, Yunnan Province in China is a major region for cut lily production, and June, July, and August each year are the peak season for gray mold, as well as the critical period for chemical control.
IV. Diagnosis
Diseased parts of lily gray mold can produce large amounts of gray mold-like growth under humid conditions. If this typical symptom is observed in the field, the disease can be correctly diagnosed. However, during the general lily growing season, this symptom is not common; instead, symptoms similar to leaf spots are more prevalent.
V. Control Methods
Use facility rain-shelter cultivation; pay attention to planting density and strengthen ventilation, which can effectively reduce the incidence of gray mold.
Cultivate disease-tolerant varieties; promote field irrigation using drip irrigation to reduce relative humidity; appropriately increase the application of calcium and potassium fertilizers to enhance disease resistance.
Promptly remove diseased leaves when found and destroy them in a centralized manner.
Disinfect bulbs before planting: Since bulbs may carry the pathogen, it is best to disinfect lily bulbs with chemicals before cultivation.
Chemical control: In the early stages of disease onset, alternately spray the foliage with agents such as Medallion, chlorothalonil, and cyprodinil every 7 to 10 days for control.
(Note: Medallion is a contact protective fungicide. Its mode of action is to inhibit the transfer related to glucose phosphorylation, thereby inhibiting the growth of the pathogen's mycelium and ultimately causing the pathogen to die.)