Control Methods and Technical Key Points for Cotton "Double Rot" Disease

Rotten bolls and rotten peaches are common, frequently occurring diseases of cotton that seriously affect cotton yield and quality. People customarily call these two diseases "double rot disease."

(1) Causes

1. Excessive or too-late application of nitrogen fertilizer causes excessive cotton growth and a closed, shaded field, which weakens the disease resistance of cotton plants.

2. During the flowering and boll stage, cotton encounters heavy rainstorms or excessive autumn rain, field humidity is too high, and drainage is poor, causing pathogens to breed and invade.

3. Cotton is attacked by red rot, anthracnose, boll blight, and other diseases.

(2) Control Measures

1. Control field humidity. Drainage and waterlogging prevention are key measures for controlling cotton rotten bolls and rotten peaches. Therefore, cotton fields should have a complete "three-ditch" system. Generally, a vertical ditch about 35 cm deep should be dug every 5 m. The drainage ditches around the field must be unobstructed, and the middle ditch, side ditch, and surrounding ditch must all connect with one another so that water dries up after the rain stops.

2. Strictly control the amount of nitrogen fertilizer applied. For both the flowering and boll fertilizer and the boll-preserving fertilizer, applying about 10 kg/mu of nitrogen fertilizer is appropriate. Too little will not increase flowering or preserve bolls and peaches, while too much will cause cotton plants to grow wildly, remain green late, mature late, and develop rotten bolls and rotten peaches. For cotton fields that have already received heavy flowering and boll fertilizer or show no tendency toward early decline, apply little or no boll-preserving fertilizer, or spray mepiquat chloride, chlormequat, and similar growth regulators to control excessive vegetative growth and reduce flower and boll shedding.

3. Prune branches to improve light conditions. For cotton fields with excessively vigorous growth, old leaves on the middle and lower parts should be removed in batches along with pruning. For cotton fields that grow wildly in autumn, remedial measures such as "opening skylights" (that is, tearing off half of each of the 2 to 3 main-stem leaves in the middle and upper parts) and pushing plants apart to air the rows should be adopted to improve ventilation and light penetration.

4. Strengthen pest and disease control. For pests such as cotton bollworm and pink bollworm, on the basis of early-stage control, apply pesticide once in each of the early, middle, and late ten-day periods of September. Methods: (1) Spray 90% trichlorfon crystal at 1000 times dilution, or 40% omethoate emulsifiable concentrate at 1000 times dilution, using 60 to 70 kg of spray solution per mu. (2) Combining pruning and bud removal with manual capture can also achieve relatively good control results. (3) For pests during the boll stage, use 25% carbendazim at 600 times dilution, or 25% phoxim emulsifiable concentrate at 600 times dilution, or 50% thiophanate at 1000 times dilution, using 60 to 65 kg of spray solution per mu, spraying once about every 15 days for 2 to 3 consecutive sprays.

5. Promptly pick rotten bolls and dry them in time. For cotton plants that already have rotten bolls or are about to develop them, pick them promptly, and take the pathogen-carrying cotton bolls out of the field to reduce sources of infection and lower the disease incidence. The promptly picked cotton bolls should be opened, dried, and stored separately in time to reduce economic losses.