What to Do When Cilantro Gets Sclerotinia Rot? A Detailed Guide to Integrated Control Methods

Cilantro, formerly known as coriander, also called fragrant coriander or hu-sui, Latin name: Coriandrum sativum L., a genus in the Apiaceae family, an annual or biennial herb with a strong odor, 20-100 cm tall. The root is spindle-shaped, slender, with numerous fine branch roots. The stem is cylindrical, erect, much branched, striped, usually smooth. The basal leaves are stalked. The styles are erect when young and curve outward when the fruit ripens. The fruit is spherical, with the main ridges on the back and the adjacent secondary ridges prominent. The endosperm is concave on the ventral side. Oil ducts are inconspicuous, or there is 1 located below the secondary ridges. Native to the Mediterranean region of Europe, it is cultivated in China in the provinces and regions of Northeast China, Hebei, Shandong, Anhui, Jiangsu, Zhejiang, Jiangxi, Hunan, Guangdong, Guangxi, Shaanxi, Sichuan, Guizhou, Yunnan, Xizang and others.

Morphological Characteristics of Cilantro

It is an annual or biennial herbaceous plant of the genus Yunjiang in the Apiaceae family. In the Shuowen Jiezi it is recorded: “Sui is written as you, and it can make the mouth fragrant. Its stem is soft, its leaves are fine, and its root has many fibers, hence sui-sui. Zhang Qian brought the seed back when he was sent to the Western Regions, hence it is called hu-sui. Sui means the appearance of stems and leaves spreading out. Shi Le tabooed the word hu, so the Jin region called it xiang-sui.”

Cilantro originated in western Asia, Persia and Egypt, and was introduced to China by Arabs during the Tang dynasty. Meng Xi's Dietary Materia Medica and Chen Zangqi's Supplements to the Materia Medica gave detailed records of this plant's properties, growth cycle, hydrological environment and so on.

Control Methods for Cilantro Sclerotinia Rot

Cilantro sclerotinia rot: in recent years, as the cilantro planting area has continued to expand, especially because crop rotation is difficult in protected cultivation, the pathogen has accumulated more and more and the damage has become increasingly serious, becoming a major obstacle in cilantro production.

Symptom Identification of Cilantro Sclerotinia Rot

Cilantro sclerotinia rot mainly damages the stem base, followed by the leaves. At first, discolored water-soaked lesions appear, then they turn light brown and rapidly expand, girdling the stem. When humidity is high, white cottony mycelium grows on the diseased part, which becomes soft and rotted. Later, below the white mold layer the mycelium forms black sclerotia. In severe cases, the diseased seedlings wither and die.

Key identification points: when moist, the surface of the diseased part bears a white cottony mold layer, and later sclerotia form on the stem surface, or black sclerotia can be seen when the stem is split open.

Occurrence Pattern of Cilantro Sclerotinia Rot

1. Pathogen Cilantro sclerotinia rot is caused by infection by Sclerotinia sclerotiorum of the genus Sclerotinia in the subphylum Ascomycotina. The mycelium is white; the sclerotium is black outside and white inside. When the sclerotium germinates it produces apothecia, sometimes as many as several dozen, generally 3-10. The apothecia are initially cup-shaped, later disc-shaped, light yellowish brown, with a long stalk below the disc. On the surface of the apothecium, asci are arranged in a club shape, each containing 8 ascospores.

2. Infection cycle The pathogen overwinters as sclerotia in the soil or mixed with seeds, becoming the primary infection source for the following year. When conditions are suitable the next year, the sclerotia germinate, produce apothecia, eject ascospores, and spread by airflow. After invading the host and causing disease, they carry out secondary infection in the field through mycelium. In the field, the disease can also spread to cilantro through weeds infected with sclerotinia rot (such as purslane), causing repeated infection. Later, when conditions deteriorate, the pathogen again forms sclerotia to overwinter.

3. Disease conditions

1) Relationship between disease occurrence and temperature and humidity The temperature range for pathogen development is 0-30℃, the optimum temperature is about 20℃, and a relative humidity above 85% favors pathogen development. Therefore, in the relatively low-temperature, high-humidity winter and spring seasons, cilantro sclerotinia rot occurs severely in protected cultivation.

2) Relationship between disease occurrence and soil moisture Sclerotia survive for a short time in water; after 1 month the sclerotia die. Therefore, in relatively moist soil, sclerotia can survive for about 1 year, while in relatively dry soil they can survive for more than 3 years. It can be seen that high soil moisture is not favorable for sclerotia survival, and disease occurrence is reduced.

3) Relationship between disease occurrence and other vegetables Because sclerotinia rot can damage almost all vegetables, the hosts include cabbage, lettuce, celery, cucumber, tomato, eggplant, kidney bean, fennel, Chinese cabbage and so on. After these vegetables develop sclerotinia rot, sclerotia are present in the soil, and planting cilantro can result in infection and disease.

4) Relationship between disease occurrence and seeds If sclerotia are mixed in with the seeds, the sclerotia enter the vegetable field with sowing and infect cilantro, causing disease.

Integrated Control Methods for Cilantro Sclerotinia Rot:

In the early stage of disease, spray 50% Sumilex wettable powder at 1000-1500 times dilution, or 50% procymidone wettable powder at 1000-1500 times dilution, or 50% iprodione wettable powder at 1000-1200 times dilution, or 50% vinclozolin wettable powder at 1000 times dilution, or 40% dimethachlon wettable powder at 1000 times dilution, or 50% chloronitroaniline wettable powder at 1000 times dilution, or 40% validamycin wettable powder at 800 times dilution, once every 7 days, spraying 2-3 times in succession. For protected cultivation, 10% Sumilex smoke agent or 15% procymidone smoke agent can be used for fumigation, 250 g each time per 666.7 sq m, in the evening; after lighting and smoke is produced, keep it closed for fumigation, once every 7 days, fumigating 4-5 times in succession.  

Other control measures:

1. Implement crop rotation or high-temperature treatment For diseased land, implement a 2-3 year rotation with grain crops. For diseased land under protected cultivation, high-temperature treatment can be adopted. The method is: during the high temperatures of the three summer months, first clean the field, remove residual branches, diseased leaves and weeds, take them out of the field and bury them deeply or burn them; apply 50-100 kg of lime per 666.7 sq m, add 500 kg of chopped wheat straw or wheat stubble, spread evenly on the soil surface, immediately plow it into the soil, form high ridges about 30 cm, and irrigate the furrows until saturated. To keep water always in the furrows, irrigate every day; cover with plastic film and seal the edges tightly with soil, and keep the shed or room closed for 15-20 days. This method can not only kill the sclerotia in the lower part, but also kill pathogens such as Fusarium and root-knot nematodes.

2. Raise seedlings in disease-free soil Seedlings should be raised in field soil or peat soil, with strengthened management, to cultivate disease-free strong seedlings. Where conditions permit, for seedbeds that have grown vegetables, heating cables can be used to raise seedlings; before sowing, adjust the seedbed temperature to 55-56℃ and treat for 2 hours, which can kill the sclerotia in the seedbed soil. Then lower the temperature, sow, and raise seedlings normally.

3. Select disease-free seeds Save seeds from disease-free plants. For seeds mixed with sclerotia, rinse the seeds with 10% salt water to remove the sclerotia. Then rinse the seeds repeatedly with clean water, dry them and sow. Seeds can also be soaked in warm water at 50℃ for 10 minutes (maintaining the temperature), which can kill the sclerotia mixed in with the seeds.

4. Strengthen ventilation For protected cultivation, ventilation should be strengthened to reduce humidity and create environmental conditions unfavorable to the development of the sclerotinia rot pathogen.

5. Cover with plastic film Plastic film can block apothecia from emerging from the soil. If UV-blocking film is used to cover the ground, the effect is even better, because this film can inhibit sclerotium germination.

6. Clean the field When diseased plants are found in the field, they should be pulled out promptly to reduce the spread of the pathogen in the field.

7. Pollution-free pesticide control For protected cultivation, before disease onset use 3.3% thiabendazole smoke agent, 250 g each time per 666.7 sq m, placed in 4-5 spots, in the evening, with closed fumigation, once every 7 days, fumigating 5-6 times in succession. In the early stage of disease, 42% thiabendazole suspension concentrate at 1000 times dilution can also be sprayed, once every 7 days, spraying 3-4 times in succession.