Occurrence Characteristics and Control Measures of Sesame Phytophthora Blight

Sesame Phytophthora blight is a devastating disease. It mainly affects the base of the sesame stem, the stem, the capsules and the leaves. After the stem base is affected, it initially appears dark green and water-soaked, then turns reddish brown, sunken, with longitudinal cracking of the cortex. After the stem and capsules are affected, the diseased parts appear dark green and water-soaked, constricted and sunken, and covered with cottony white mold. After the leaves are affected, yellow-brown lesions appear, and the lesions have indistinct concentric rings. The pathogen of this disease overwinters in diseased plant residues as mycelium or oospores. The following year, the pathogen infects the stem base, produces sporangia, and spreads by wind, rain and flowing water, causing expanded secondary infection. The disease begins in July during the sesame budding stage and reaches its peak in August. Damage is severe under rainy and humid conditions.

Control techniques:

1. Select resistant varieties and treat seeds. Choose varieties with good quality and high yield, tolerance to waterlogging and strong disease resistance, such as Yuzhi No. 8, Yizhi No. 1, etc. Before sowing, soak the seeds in warm water at 55°C for 10 minutes or at 60°C for 5 minutes, then dry them and sow. Alternatively, treat the seeds with quintozene plus thiram (1:1) at a rate of 0.5-1% of the seed weight; or soak the seeds in a 0.5% copper sulfate solution for half an hour. All of these give good control effects.

2. Agricultural control. Soil-borne diseases and insect pests of sesame are serious, and continuous cropping is most taboo. A 3-5 year rotation of sesame with cotton, sweet potato and gramineous crops can better control the occurrence and spread of the disease. After harvesting sesame, promptly remove diseased residues from the field and burn or deeply bury them in a centralized manner to reduce overwintering inoculum. Promptly pull out diseased plants and carry them out of the field for destruction to prevent the pathogen from spreading. Strengthen fertilizer and water management, apply more basal fertilizer, with basal fertilizer mainly consisting of medium- and slow-release organic fertilizer, and mix in phosphorus and potassium fertilizer. Apply no or little nitrogen fertilizer at the seedling stage to cultivate healthy seedlings so that the pathogen is less likely to invade. Adopt raised-bed cultivation, promptly clean ditches and drain water, prevent standing water in the field, and reduce field humidity.

3. Chemical control. Control of sesame diseases should be based mainly on agricultural control. For chemical control, spray to protect before the disease occurs, or apply chemicals at the early stage of disease onset. Control agents include 37% Kuwei Like wettable powder at 800 times dilution, 40% carbendazim suspension concentrate at 700 times dilution, 50% thiophanate-methyl wettable powder at 800-1000 times dilution, 80% copper sulfate wettable powder at 800 times dilution, etc.