What are the main diseases of rhubarb? How to prevent it?

The main diseases of rhubarb are root rot, rhubarb ring rot, scab, rhubarb anthracnose and rhubarb downy mildew

(1) root rot

It is often easy to get sick in the case of high temperature and high humidity in the year of harvest or July-August of the previous year, and it is most serious in wet continuous cropping plots. After the onset, wet and irregular brown spots appeared on the underground rhizome of rhubarb at first, then expanded rapidly, penetrated into the rhizome and spread around to rot, resulting in all the rhizomes turning black. The aboveground part starts from the base of the petiole at the outer edge of the plant and gradually spreads, making the petiole completely black, leading to the death of the whole plant.

Integrated control technology

① Implement crop rotation. Rotation with leguminous and gramineous crops, rotation with codonopsis pilosula and coptis chinensis.

(2) Keep the soil well drained or make the frame into a turtle back shape to facilitate drainage.

③ Remove the diseased plants and burn them as soon as possible, and disinfect the soil at the diseased plants with lime to avoid the spread of pathogens.

(4) Remove litter and weeds, and eliminate winter germs.

⑤ Spray or water with 800 times solution of 77% propargite wettable powder or 500 ~ 600 times solution of 80% mancozeb wettable powder every 7 ~ 10 day for 3 ~ 4 times continuously.

(2) Rhubarb ring rot

After the leaves were damaged, the lesion was nearly round, with a diameter of 1 ~ 2 cm, reddish brown, concentric wheel lines and dark brown spots inside, which were conidia of pathogenic bacteria. When the disease is serious, the leaves will die. Rhubarb ring rot will occur soon after emergence and last until harvest. Pathogenic bacteria overwinter on diseased spots or buds with hyphae and spread by wind and rain.

Preventive and control measures

(1) Remove dead leaves in late autumn and early winter to reduce overwintering bacteria sources.

② Strengthen early intertillage weeding, apply more organic fertilizer and improve disease resistance.

③ From/0/5th day after emergence, spraying 800 times of 77% herbicide or 600 times of 75% mancozeb wettable powder continuously.

(3) Rhubarb Anthracnose

After the rhubarb leaves are damaged, the diseased spots are round or nearly round, with a diameter of 2 ~ 4 cm, a light brown center and purple-red edges, and then purple-black spots are produced, that is, the bacteria have no umbilicus, but they are not easy to see with the naked eye. Finally, the lesion is often perforated.

Preventive and control measures

The occurrence time of anthracnose is generally earlier, so we can refer to the prevention and treatment of ring rot.

(4) Downy mildew of rhubarb

The lesions on the leaves are polygonal to irregular, yellow-green, and the edges are not obvious. When the disease is serious, the leaves turn yellow and gradually dry up. When the weather is wet, purple frosty mildew layer can be seen at the diseased spot on the back of the leaf.

Occurrence law

Pathogens overwinter in the lesion of damaged leaves in the form of oospores. In the next spring, when the conditions are suitable, oospores germinate and release zoospores, which spread by wind and rain and invade from the stomata of the host. It is easy to occur under the conditions of low temperature and high humidity. Generally, the disease begins in the middle and late April, and it is serious in May-June.

Preventive and control measures

① Implement crop rotation to keep good soil drainage.

② Pull out the diseased plants in time and burn them. Disinfect the diseased soil with lime, remove litter and weeds in the field, and eliminate the source of overwintering bacteria.

③80% mancozeb wettable powder is sprayed with 500-600 times solution, or 800 times solution of metalaxyl mancozeb wettable powder is sprayed every 7- 10 day for 3-4 times continuously.