How to Control Anthracnose in Bok Choy? Leaf White Spot Symptom Identification and Fungicide Methods

Those who have grown bok choy may have encountered this situation: spots with white centers and brown edges appear on the leaves, and brown elongated streaks also form on the petioles. This is most likely anthracnose. This disease is most likely to occur from June to September each year. The hot and rainy season happens to coincide with the peak growing season for bok choy. If not controlled in time, the marketability of the leaves will be greatly reduced.

Recognizing the Symptoms: White Spots on Leaves, Brown Spots on Petioles

Bok choy anthracnose mainly damages the leaves and sometimes also infects the petioles. In the early stage of leaf infection, nearly circular sunken lesions appear, white in the center and brown at the edges; in the later stage, the lesions turn white or grayish-white and become semi-transparent, and they easily perforate in dry weather. On the petioles, long elliptical or spindle-shaped lesions mostly form, yellow-brown to gray-brown in color, with slightly darker and somewhat sunken edges. In the later stage, the lesions often split open on both sides.

Which plots are prone to the disease? Fields planted too densely, with poor ventilation and closed-in canopies, with more rain, and prone to water accumulation after rain are the hardest hit; in addition, when fertilizer and water are usually lacking and plant growth is poor, the disease tends to be more severe. Therefore, control should start with cultivation management.

Agricultural Control: Manage Density, Fertilizer and Water, and Field Cleanliness

First, arrange the planting density reasonably. Do not plant too densely out of greed for more plants, and ensure ventilation and light penetration in the field; at the same time, strengthen fertilizer and water management to promote vigorous growth of bok choy, so its disease resistance will naturally be stronger; after rain, promptly drain accumulated water from the field, and do not let the roots soak in water. After harvest is completed, promptly remove diseased and residual plants from the field, carry them out of the field and destroy them centrally to reduce residual sources of disease.

Seed treatment before sowing is also very effective: use 25% bromothalonil wettable powder or 50% prochloraz manganese complex wettable powder, and dress the seeds at 0.3%-0.4% of the weight of bok choy seeds; seed coating with 2.5% fludioxonil suspension seed coating agent can also be used to block the pathogen before germination.

Chemical Control: Spray Promptly at the Early Stage of Disease, 2-3 Consecutive Sprays at 7-10 Day Intervals

Once lesions appear in the field, seize the early stage of disease and apply chemicals promptly. Any one of the following formulas can be selected and sprayed after dilution with water: 20% pyraclostrobin water-dispersible granules 1000-1500 times solution + 80% zineb wettable powder 600-800 times solution; or 20% difenoconazole·prochloraz microemulsion 2500-3500 times solution; or 50% kresoxim-methyl dry suspension concentrate 3000 times solution + 70% propineb wettable powder 600-800 times solution; or 30% benazolin? Please note: the source text appears to be 30% benzothiocyanate? If needed, I can provide a corrected technical translation.